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<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.134 2006/09/22 23:20:13 tgl Exp $ -->
<!--
Documentation of the system catalogs, directed toward PostgreSQL developers
-->
<chapter id="catalogs">
<title>System Catalogs</title>
<para>
The system catalogs are the place where a relational database
management system stores schema metadata, such as information about
tables and columns, and internal bookkeeping information.
<productname>PostgreSQL</productname>'s system catalogs are regular
tables. You can drop and recreate the tables, add columns, insert
and update values, and severely mess up your system that way.
Normally, one should not change the system catalogs by hand, there
are always SQL commands to do that. (For example, <command>CREATE
DATABASE</command> inserts a row into the
<structname>pg_database</structname> catalog &mdash; and actually
creates the database on disk.) There are some exceptions for
particularly esoteric operations, such as adding index access methods.
</para>
<sect1 id="catalogs-overview">
<title>Overview</title>
<para>
<xref linkend="catalog-table"> lists the system catalogs.
More detailed documentation of each catalog follows below.
</para>
<para>
Most system catalogs are copied from the template database during
database creation and are thereafter database-specific. A few
catalogs are physically shared across all databases in a cluster;
these are noted in the descriptions of the individual catalogs.
</para>
<table id="catalog-table">
<title>System Catalogs</title>
<tgroup cols="2">
<thead>
<row>
<entry>Catalog Name</entry>
<entry>Purpose</entry>
</row>
</thead>
<tbody>
<row>
<entry><link linkend="catalog-pg-aggregate"><structname>pg_aggregate</structname></link></entry>
<entry>aggregate functions</entry>
</row>
<row>
<entry><link linkend="catalog-pg-am"><structname>pg_am</structname></link></entry>
<entry>index access methods</entry>
</row>
<row>
<entry><link linkend="catalog-pg-amop"><structname>pg_amop</structname></link></entry>
<entry>access method operators</entry>
</row>
<row>
<entry><link linkend="catalog-pg-amproc"><structname>pg_amproc</structname></link></entry>
<entry>access method support procedures</entry>
</row>
<row>
<entry><link linkend="catalog-pg-attrdef"><structname>pg_attrdef</structname></link></entry>
<entry>column default values</entry>
</row>
<row>
<entry><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link></entry>
<entry>table columns (<quote>attributes</quote>)</entry>
</row>
<row>
<entry><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link></entry>
<entry>authorization identifiers (roles)</entry>
</row>
<row>
<entry><link linkend="catalog-pg-auth-members"><structname>pg_auth_members</structname></link></entry>
<entry>authorization identifier membership relationships</entry>
</row>
<row>
<entry><link linkend="catalog-pg-autovacuum"><structname>pg_autovacuum</structname></link></entry>
<entry>per-relation autovacuum configuration parameters</entry>
</row>
<row>
<entry><link linkend="catalog-pg-cast"><structname>pg_cast</structname></link></entry>
<entry>casts (data type conversions)</entry>
</row>
<row>
<entry><link linkend="catalog-pg-class"><structname>pg_class</structname></link></entry>
<entry>tables, indexes, sequences, views (<quote>relations</quote>)</entry>
</row>
<row>
<entry><link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link></entry>
<entry>check constraints, unique constraints, primary key constraints, foreign key constraints</entry>
</row>
<row>
<entry><link linkend="catalog-pg-conversion"><structname>pg_conversion</structname></link></entry>
<entry>encoding conversion information</entry>
</row>
<row>
<entry><link linkend="catalog-pg-database"><structname>pg_database</structname></link></entry>
<entry>databases within this database cluster</entry>
</row>
<row>
<entry><link linkend="catalog-pg-depend"><structname>pg_depend</structname></link></entry>
<entry>dependencies between database objects</entry>
</row>
<row>
<entry><link linkend="catalog-pg-description"><structname>pg_description</structname></link></entry>
<entry>descriptions or comments on database objects</entry>
</row>
<row>
<entry><link linkend="catalog-pg-index"><structname>pg_index</structname></link></entry>
<entry>additional index information</entry>
</row>
<row>
<entry><link linkend="catalog-pg-inherits"><structname>pg_inherits</structname></link></entry>
<entry>table inheritance hierarchy</entry>
</row>
<row>
<entry><link linkend="catalog-pg-language"><structname>pg_language</structname></link></entry>
<entry>languages for writing functions</entry>
</row>
<row>
<entry><link linkend="catalog-pg-largeobject"><structname>pg_largeobject</structname></link></entry>
<entry>large objects</entry>
</row>
<row>
<entry><link linkend="catalog-pg-listener"><structname>pg_listener</structname></link></entry>
<entry>asynchronous notification support</entry>
</row>
<row>
<entry><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link></entry>
<entry>schemas</entry>
</row>
<row>
<entry><link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link></entry>
<entry>index access method operator classes</entry>
</row>
<row>
<entry><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link></entry>
<entry>operators</entry>
</row>
<row>
<entry><link linkend="catalog-pg-pltemplate"><structname>pg_pltemplate</structname></link></entry>
<entry>template data for procedural languages</entry>
</row>
<row>
<entry><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link></entry>
<entry>functions and procedures</entry>
</row>
<row>
<entry><link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link></entry>
<entry>query rewrite rules</entry>
</row>
<row>
<entry><link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link></entry>
<entry>dependencies on shared objects</entry>
</row>
<row>
<entry><link linkend="catalog-pg-shdescription"><structname>pg_shdescription</structname></link></entry>
<entry>comments on shared objects</entry>
</row>
<row>
<entry><link linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link></entry>
<entry>planner statistics</entry>
</row>
<row>
<entry><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link></entry>
<entry>tablespaces within this database cluster</entry>
</row>
<row>
<entry><link linkend="catalog-pg-trigger"><structname>pg_trigger</structname></link></entry>
<entry>triggers</entry>
</row>
<row>
<entry><link linkend="catalog-pg-type"><structname>pg_type</structname></link></entry>
<entry>data types</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-aggregate">
<title><structname>pg_aggregate</structname></title>
<indexterm zone="catalog-pg-aggregate">
<primary>pg_aggregate</primary>
</indexterm>
<para>
The catalog <structname>pg_aggregate</structname> stores information about
aggregate functions. An aggregate function is a function that
operates on a set of values (typically one column from each row
that matches a query condition) and returns a single value computed
from all these values. Typical aggregate functions are
<function>sum</function>, <function>count</function>, and
<function>max</function>. Each entry in
<structname>pg_aggregate</structname> is an extension of an entry
in <structname>pg_proc</structname>. The <structname>pg_proc</structname>
entry carries the aggregate's name, input and output data types, and
other information that is similar to ordinary functions.
</para>
<table>
<title><structname>pg_aggregate</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>aggfnoid</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><structname>pg_proc</structname> OID of the aggregate function</entry>
</row>
<row>
<entry><structfield>aggtransfn</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Transition function</entry>
</row>
<row>
<entry><structfield>aggfinalfn</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Final function (zero if none)</entry>
</row>
<row>
<entry><structfield>aggsortop</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
<entry>Associated sort operator (zero if none)</entry>
</row>
<row>
<entry><structfield>aggtranstype</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>Data type of the aggregate function's internal transition (state) data</entry>
</row>
<row>
<entry><structfield>agginitval</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>
The initial value of the transition state. This is a text
field containing the initial value in its external string
representation. If this field is NULL, the transition state
value starts out NULL.
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
New aggregate functions are registered with the <xref
linkend="sql-createaggregate" endterm="sql-createaggregate-title">
command. See <xref linkend="xaggr"> for more information about
writing aggregate functions and the meaning of the transition
functions, etc.
</para>
</sect1>
<sect1 id="catalog-pg-am">
<title><structname>pg_am</structname></title>
<indexterm zone="catalog-pg-am">
<primary>pg_am</primary>
</indexterm>
<para>
The catalog <structname>pg_am</structname> stores information about index
access methods. There is one row for each index access method supported by
the system. The contents of this catalog are discussed in detail in
<xref linkend="indexam">.
</para>
<table>
<title><structname>pg_am</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>amname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Name of the access method</entry>
</row>
<row>
<entry><structfield>amstrategies</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Number of operator strategies for this access method</entry>
</row>
<row>
<entry><structfield>amsupport</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Number of support routines for this access method</entry>
</row>
<row>
<entry><structfield>amorderstrategy</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Zero if the index offers no sort order, otherwise the strategy
number of the strategy operator that describes the sort order</entry>
</row>
<row>
<entry><structfield>amcanunique</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Does the access method support unique indexes?</entry>
</row>
<row>
<entry><structfield>amcanmulticol</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Does the access method support multicolumn indexes?</entry>
</row>
<row>
<entry><structfield>amoptionalkey</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Does the access method support a scan without any constraint
for the first index column?</entry>
</row>
<row>
<entry><structfield>amindexnulls</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Does the access method support null index entries?</entry>
</row>
<row>
<entry><structfield>amstorage</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Can index storage data type differ from column data type?</entry>
</row>
<row>
<entry><structfield>amclusterable</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Can an index of this type be CLUSTERed on?</entry>
</row>
<row>
<entry><structfield>aminsert</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><quote>Insert this tuple</quote> function</entry>
</row>
<row>
<entry><structfield>ambeginscan</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><quote>Start new scan</quote> function</entry>
</row>
<row>
<entry><structfield>amgettuple</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><quote>Next valid tuple</quote> function</entry>
</row>
<row>
<entry><structfield>amgetmulti</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><quote>Fetch multiple tuples</quote> function</entry>
</row>
<row>
<entry><structfield>amrescan</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><quote>Restart this scan</quote> function</entry>
</row>
<row>
<entry><structfield>amendscan</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><quote>End this scan</quote> function</entry>
</row>
<row>
<entry><structfield>ammarkpos</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><quote>Mark current scan position</quote> function</entry>
</row>
<row>
<entry><structfield>amrestrpos</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><quote>Restore marked scan position</quote> function</entry>
</row>
<row>
<entry><structfield>ambuild</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><quote>Build new index</quote> function</entry>
</row>
<row>
<entry><structfield>ambulkdelete</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Bulk-delete function</entry>
</row>
<row>
<entry><structfield>amvacuumcleanup</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Post-<command>VACUUM</command> cleanup function</entry>
</row>
<row>
<entry><structfield>amcostestimate</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Function to estimate cost of an index scan</entry>
</row>
<row>
<entry><structfield>amoptions</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Function to parse and validate reloptions for an index</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-amop">
<title><structname>pg_amop</structname></title>
<indexterm zone="catalog-pg-amop">
<primary>pg_amop</primary>
</indexterm>
<para>
The catalog <structname>pg_amop</structname> stores information about operators
associated with index access method operator classes. There is one
row for each operator that is a member of an operator class.
</para>
<table>
<title><structname>pg_amop</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>amopclaid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.oid</literal></entry>
<entry>The index operator class this entry is for</entry>
</row>
<row>
<entry><structfield>amopsubtype</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>Subtype to distinguish multiple entries for one strategy;
zero for default</entry>
</row>
<row>
<entry><structfield>amopstrategy</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Operator strategy number</entry>
</row>
<row>
<entry><structfield>amopreqcheck</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Index hit must be rechecked</entry>
</row>
<row>
<entry><structfield>amopopr</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
<entry>OID of the operator</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-amproc">
<title><structname>pg_amproc</structname></title>
<indexterm zone="catalog-pg-amproc">
<primary>pg_amproc</primary>
</indexterm>
<para>
The catalog <structname>pg_amproc</structname> stores information about support
procedures
associated with index access method operator classes. There is one
row for each support procedure belonging to an operator class.
</para>
<table>
<title><structname>pg_amproc</structname> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>amopclaid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.oid</literal></entry>
<entry>The index operator class this entry is for</entry>
</row>
<row>
<entry><structfield>amprocsubtype</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>Subtype, if cross-type routine, else zero</entry>
</row>
<row>
<entry><structfield>amprocnum</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Support procedure number</entry>
</row>
<row>
<entry><structfield>amproc</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>OID of the procedure</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-attrdef">
<title><structname>pg_attrdef</structname></title>
<indexterm zone="catalog-pg-attrdef">
<primary>pg_attrdef</primary>
</indexterm>
<para>
The catalog <structname>pg_attrdef</structname> stores column default values. The main information
about columns is stored in <structname>pg_attribute</structname>
(see below). Only columns that explicitly specify a default value
(when the table is created or the column is added) will have an
entry here.
</para>
<table>
<title><structname>pg_attrdef</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>adrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The table this column belongs to</entry>
</row>
<row>
<entry><structfield>adnum</structfield></entry>
<entry><type>int2</type></entry>
<entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry>
<entry>The number of the column</entry>
</row>
<row>
<entry><structfield>adbin</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>The internal representation of the column default value</entry>
</row>
<row>
<entry><structfield>adsrc</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>A human-readable representation of the default value</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <structfield>adsrc</structfield> field is historical, and is best
not used, because it does not track outside changes that might affect
the representation of the default value. Reverse-compiling the
<structfield>adbin</structfield> field (with <function>pg_get_expr</> for
example) is a better way to display the default value.
</para>
</sect1>
<sect1 id="catalog-pg-attribute">
<title><structname>pg_attribute</structname></title>
<indexterm zone="catalog-pg-attribute">
<primary>pg_attribute</primary>
</indexterm>
<para>
The catalog <structname>pg_attribute</structname> stores information about
table columns. There will be exactly one
<structname>pg_attribute</structname> row for every column in every
table in the database. (There will also be attribute entries for
indexes, and indeed all objects that have <structname>pg_class</structname>
entries.)
</para>
<para>
The term attribute is equivalent to column and is used for
historical reasons.
</para>
<table>
<title><structname>pg_attribute</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>attrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The table this column belongs to</entry>
</row>
<row>
<entry><structfield>attname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>The column name</entry>
</row>
<row>
<entry><structfield>atttypid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>The data type of this column</entry>
</row>
<row>
<entry><structfield>attstattarget</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
<structfield>attstattarget</structfield> controls the level of detail
of statistics accumulated for this column by
<xref linkend="sql-analyze" endterm="sql-analyze-title">.
A zero value indicates that no statistics should be collected.
A negative value says to use the system default statistics target.
The exact meaning of positive values is data type-dependent.
For scalar data types, <structfield>attstattarget</structfield>
is both the target number of <quote>most common values</quote>
to collect, and the target number of histogram bins to create.
</entry>
</row>
<row>
<entry><structfield>attlen</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>
A copy of <literal>pg_type.typlen</literal> of this column's
type
</entry>
</row>
<row>
<entry><structfield>attnum</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>
The number of the column. Ordinary columns are numbered from 1
up. System columns, such as <structfield>oid</structfield>,
have (arbitrary) negative numbers.
</entry>
</row>
<row>
<entry><structfield>attndims</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
Number of dimensions, if the column is an array type; otherwise 0.
(Presently, the number of dimensions of an array is not enforced,
so any nonzero value effectively means <quote>it's an array</>.)
</entry>
</row>
<row>
<entry><structfield>attcacheoff</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
Always -1 in storage, but when loaded into a row descriptor
in memory this may be updated to cache the offset of the attribute
within the row.
</entry>
</row>
<row>
<entry><structfield>atttypmod</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
<structfield>atttypmod</structfield> records type-specific data
supplied at table creation time (for example, the maximum
length of a <type>varchar</type> column). It is passed to
type-specific input functions and length coercion functions.
The value will generally be -1 for types that do not need <structfield>atttypmod</>.
</entry>
</row>
<row>
<entry><structfield>attbyval</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
A copy of <literal>pg_type.typbyval</> of this column's type
</entry>
</row>
<row>
<entry><structfield>attstorage</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
Normally a copy of <literal>pg_type.typstorage</> of this
column's type. For TOAST-able data types, this can be altered
after column creation to control storage policy.
</entry>
</row>
<row>
<entry><structfield>attalign</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
A copy of <literal>pg_type.typalign</> of this column's type
</entry>
</row>
<row>
<entry><structfield>attnotnull</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
This represents a not-null constraint. It is possible to
change this column to enable or disable the constraint.
</entry>
</row>
<row>
<entry><structfield>atthasdef</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
This column has a default value, in which case there will be a
corresponding entry in the <structname>pg_attrdef</structname>
catalog that actually defines the value.
</entry>
</row>
<row>
<entry><structfield>attisdropped</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
This column has been dropped and is no longer valid. A dropped
column is still physically present in the table, but is
ignored by the parser and so cannot be accessed via SQL.
</entry>
</row>
<row>
<entry><structfield>attislocal</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
This column is defined locally in the relation. Note that a column may
be locally defined and inherited simultaneously.
</entry>
</row>
<row>
<entry><structfield>attinhcount</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
The number of direct ancestors this column has. A column with a
nonzero number of ancestors cannot be dropped nor renamed.
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
In a dropped column's <structname>pg_attribute</structname> entry,
<structfield>atttypid</structfield> is reset to zero, but
<structfield>attlen</structfield> and the other fields copied from
<structname>pg_type</> are still valid. This arrangement is needed
to cope with the situation where the dropped column's data type was
later dropped, and so there is no <structname>pg_type</> row anymore.
<structfield>attlen</structfield> and the other fields can be used
to interpret the contents of a row of the table.
</para>
</sect1>
<sect1 id="catalog-pg-authid">
<title><structname>pg_authid</structname></title>
<indexterm zone="catalog-pg-authid">
<primary>pg_authid</primary>
</indexterm>
<para>
The catalog <structname>pg_authid</structname> contains information about
database authorization identifiers (roles). A role subsumes the concepts
of <quote>users</> and <quote>groups</>. A user is essentially just a
role with the <structfield>rolcanlogin</> flag set. Any role (with or
without <structfield>rolcanlogin</>) may have other roles as members; see
<link linkend="catalog-pg-auth-members"><structname>pg_auth_members</structname></link>.
</para>
<para>
Since this catalog contains passwords, it must not be publicly readable.
<link linkend="view-pg-roles"><structname>pg_roles</structname></link>
is a publicly readable view on
<structname>pg_authid</structname> that blanks out the password field.
</para>
<para>
<xref linkend="user-manag"> contains detailed information about user and
privilege management.
</para>
<para>
Because user identities are cluster-wide,
<structname>pg_authid</structname>
is shared across all databases of a cluster: there is only one
copy of <structname>pg_authid</structname> per cluster, not
one per database.
</para>
<table>
<title><structname>pg_authid</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>rolname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Role name</entry>
</row>
<row>
<entry><structfield>rolsuper</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Role has superuser privileges</entry>
</row>
<row>
<entry><structfield>rolinherit</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Role automatically inherits privileges of roles it is a
member of</entry>
</row>
<row>
<entry><structfield>rolcreaterole</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Role may create more roles</entry>
</row>
<row>
<entry><structfield>rolcreatedb</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Role may create databases</entry>
</row>
<row>
<entry><structfield>rolcatupdate</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
Role may update system catalogs directly. (Even a superuser may not do
this unless this column is true.)
</entry>
</row>
<row>
<entry><structfield>rolcanlogin</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
Role may log in. That is, this role can be given as the initial
session authorization identifier.
</entry>
</row>
<row>
<entry><structfield>rolconnlimit</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
For roles that can log in, this sets maximum number of concurrent
connections this role can make. -1 means no limit.
</entry>
</row>
<row>
<entry><structfield>rolpassword</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Password (possibly encrypted); NULL if none</entry>
</row>
<row>
<entry><structfield>rolvaliduntil</structfield></entry>
<entry><type>timestamptz</type></entry>
<entry></entry>
<entry>Password expiry time (only used for password authentication);
NULL if no expiration</entry>
</row>
<row>
<entry><structfield>rolconfig</structfield></entry>
<entry><type>text[]</type></entry>
<entry></entry>
<entry>Session defaults for run-time configuration variables</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-auth-members">
<title><structname>pg_auth_members</structname></title>
<indexterm zone="catalog-pg-auth-members">
<primary>pg_auth_members</primary>
</indexterm>
<para>
The catalog <structname>pg_auth_members</structname> shows the membership
relations between roles. Any non-circular set of relationships is allowed.
</para>
<para>
Because user identities are cluster-wide,
<structname>pg_auth_members</structname>
is shared across all databases of a cluster: there is only one
copy of <structname>pg_auth_members</structname> per cluster, not
one per database.
</para>
<table>
<title><structname>pg_auth_members</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>roleid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>ID of a role that has a member</entry>
</row>
<row>
<entry><structfield>member</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>ID of a role that is a member of <structfield>roleid</></entry>
</row>
<row>
<entry><structfield>grantor</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>ID of the role that granted this membership</entry>
</row>
<row>
<entry><structfield>admin_option</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if <structfield>member</> may grant membership in
<structfield>roleid</> to others</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-autovacuum">
<title><structname>pg_autovacuum</structname></title>
<indexterm zone="catalog-pg-autovacuum">
<primary>pg_autovacuum</primary>
</indexterm>
<indexterm zone="catalog-pg-autovacuum">
<primary>autovacuum</primary>
<secondary>table-specific configuration</secondary>
</indexterm>
<para>
The catalog <structname>pg_autovacuum</structname> stores optional
per-relation configuration parameters for <xref linkend="autovacuum" endterm="autovacuum-title">.
If there is an entry here for a particular relation, the given
parameters will be used for autovacuuming that table. If no entry
is present, the system-wide defaults will be used.
</para>
<table>
<title><structname>pg_autovacuum</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>vacrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The table this entry is for</entry>
</row>
<row>
<entry><structfield>enabled</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>If false, this table is never autovacuumed</entry>
</row>
<row>
<entry><structfield>vac_base_thresh</structfield></entry>
<entry><type>integer</type></entry>
<entry></entry>
<entry>Minimum number of modified tuples before vacuum</entry>
</row>
<row>
<entry><structfield>vac_scale_factor</structfield></entry>
<entry><type>float4</type></entry>
<entry></entry>
<entry>Multiplier for reltuples to add to
<structfield>vac_base_thresh</></entry>
</row>
<row>
<entry><structfield>anl_base_thresh</structfield></entry>
<entry><type>integer</type></entry>
<entry></entry>
<entry>Minimum number of modified tuples before analyze</entry>
</row>
<row>
<entry><structfield>anl_scale_factor</structfield></entry>
<entry><type>float4</type></entry>
<entry></entry>
<entry>Multiplier for reltuples to add to
<structfield>anl_base_thresh</></entry>
</row>
<row>
<entry><structfield>vac_cost_delay</structfield></entry>
<entry><type>integer</type></entry>
<entry></entry>
<entry>Custom <varname>vacuum_cost_delay</> parameter</entry>
</row>
<row>
<entry><structfield>vac_cost_limit</structfield></entry>
<entry><type>integer</type></entry>
<entry></entry>
<entry>Custom <varname>vacuum_cost_limit</> parameter</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The autovacuum daemon will initiate a <command>VACUUM</> operation
on a particular table when the number of updated or deleted tuples
exceeds <structfield>vac_base_thresh</structfield> plus
<structfield>vac_scale_factor</structfield> times the number of
live tuples currently estimated to be in the relation.
Similarly, it will initiate an <command>ANALYZE</> operation
when the number of inserted, updated or deleted tuples
exceeds <structfield>anl_base_thresh</structfield> plus
<structfield>anl_scale_factor</structfield> times the number of
live tuples currently estimated to be in the relation.
</para>
<para>
Any of the numerical fields can contain <literal>-1</> (or indeed
any negative value) to indicate that the system-wide default should
be used for this particular value. Observe that the
<structfield>vac_cost_delay</> variable inherits its default value from the
<varname>autovacuum_vacuum_cost_delay</> configuration parameter,
or from <varname>vacuum_cost_delay</> if the former is set to a negative
value. The same applies to <structfield>vac_cost_limit</>.
</para>
</sect1>
<sect1 id="catalog-pg-cast">
<title><structname>pg_cast</structname></title>
<indexterm zone="catalog-pg-cast">
<primary>pg_cast</primary>
</indexterm>
<para>
The catalog <structname>pg_cast</structname> stores data type conversion paths,
both built-in paths and those defined with <command>CREATE CAST</command>.
</para>
<table>
<title><structfield>pg_cast</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>castsource</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>OID of the source data type</entry>
</row>
<row>
<entry><structfield>casttarget</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>OID of the target data type</entry>
</row>
<row>
<entry><structfield>castfunc</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>
The OID of the function to use to perform this cast. Zero is
stored if the data types are binary compatible (that is, no
run-time operation is needed to perform the cast).
</entry>
</row>
<row>
<entry><structfield>castcontext</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
Indicates what contexts the cast may be invoked in.
<literal>e</> means only as an explicit cast (using
<literal>CAST</> or <literal>::</> syntax).
<literal>a</> means implicitly in assignment
to a target column, as well as explicitly.
<literal>i</> means implicitly in expressions, as well as the
other cases.
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The cast functions listed in <structname>pg_cast</structname> must
always take the cast source type as their first argument type, and
return the cast destination type as their result type. A cast
function can have up to three arguments. The second argument,
if present, must be type <type>integer</>; it receives the type
modifier associated with the destination type, or <literal>-1</>
if there is none. The third argument,
if present, must be type <type>boolean</>; it receives <literal>true</>
if the cast is an explicit cast, <literal>false</> otherwise.
</para>
<para>
It is legitimate to create a <structname>pg_cast</structname> entry
in which the source and target types are the same, if the associated
function takes more than one argument. Such entries represent
<quote>length coercion functions</> that coerce values of the type
to be legal for a particular type modifier value. Note however that
at present there is no support for associating non-default type
modifiers with user-created data types, and so this facility is only
of use for the small number of built-in types that have type modifier
syntax built into the grammar.
</para>
<para>
When a <structname>pg_cast</structname> entry has different source and
target types and a function that takes more than one argument, it
represents converting from one type to another and applying a length
coercion in a single step. When no such entry is available, coercion
to a type that uses a type modifier involves two steps, one to
convert between data types and a second to apply the modifier.
</para>
</sect1>
<sect1 id="catalog-pg-class">
<title><structname>pg_class</structname></title>
<indexterm zone="catalog-pg-class">
<primary>pg_class</primary>
</indexterm>
<para>
The catalog <structname>pg_class</structname> catalogs tables and most
everything else that has columns or is otherwise similar to a
table. This includes indexes (but see also
<structname>pg_index</structname>), sequences, views, composite types,
and TOAST tables; see <structfield>relkind</>.
Below, when we mean all of these
kinds of objects we speak of <quote>relations</quote>. Not all
columns are meaningful for all relation types.
</para>
<table>
<title><structname>pg_class</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>relname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Name of the table, index, view, etc.</entry>
</row>
<row>
<entry><structfield>relnamespace</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
<entry>
The OID of the namespace that contains this relation
</entry>
</row>
<row>
<entry><structfield>reltype</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>
The OID of the data type that corresponds to this table's row type,
if any (zero for indexes, which have no <structname>pg_type</> entry)
</entry>
</row>
<row>
<entry><structfield>relowner</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>Owner of the relation</entry>
</row>
<row>
<entry><structfield>relam</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
<entry>If this is an index, the access method used (B-tree, hash, etc.)</entry>
</row>
<row>
<entry><structfield>relfilenode</structfield></entry>
<entry><type>oid</type></entry>
<entry></entry>
<entry>Name of the on-disk file of this relation; 0 if none</entry>
</row>
<row>
<entry><structfield>reltablespace</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.oid</literal></entry>
<entry>
The tablespace in which this relation is stored. If zero,
the database's default tablespace is implied. (Not meaningful
if the relation has no on-disk file.)
</entry>
</row>
<row>
<entry><structfield>relpages</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
Size of the on-disk representation of this table in pages (of size
<symbol>BLCKSZ</symbol>).
This is only an estimate used by the planner.
It is updated by <command>VACUUM</command>,
<command>ANALYZE</command>, and a few DDL commands
such as <command>CREATE INDEX</command>.
</entry>
</row>
<row>
<entry><structfield>reltuples</structfield></entry>
<entry><type>float4</type></entry>
<entry></entry>
<entry>
Number of rows in the table.
This is only an estimate used by the planner.
It is updated by <command>VACUUM</command>,
<command>ANALYZE</command>, and a few DDL commands
such as <command>CREATE INDEX</command>.
</entry>
</row>
<row>
<entry><structfield>reltoastrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>
OID of the TOAST table associated with this table, 0 if none.
The TOAST table stores large attributes <quote>out of
line</quote> in a secondary table.
</entry>
</row>
<row>
<entry><structfield>reltoastidxid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>
For a TOAST table, the OID of its index. 0 if not a TOAST table.
</entry>
</row>
<row>
<entry><structfield>relhasindex</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
True if this is a table and it has (or recently had) any
indexes. This is set by <command>CREATE INDEX</command>, but
not cleared immediately by <command>DROP INDEX</command>.
<command>VACUUM</command> clears <structfield>relhasindex</> if it finds the
table has no indexes.
</entry>
</row>
<row>
<entry><structfield>relisshared</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if this table is shared across all databases in the
cluster. Only certain system catalogs (such as
<structname>pg_database</structname>) are shared.</entry>
</row>
<row>
<entry><structfield>relkind</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
<literal>r</> = ordinary table, <literal>i</> = index,
<literal>S</> = sequence, <literal>v</> = view, <literal>c</> =
composite type, <literal>t</> = TOAST
table
</entry>
</row>
<row>
<entry><structfield>relnatts</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>
Number of user columns in the relation (system columns not
counted). There must be this many corresponding entries in
<structname>pg_attribute</structname>. See also
<literal>pg_attribute.attnum</literal>.
</entry>
</row>
<row>
<entry><structfield>relchecks</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>
Number of check constraints on the table; see
<structname>pg_constraint</structname> catalog
</entry>
</row>
<row>
<entry><structfield>reltriggers</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>
Number of triggers on the table; see
<structname>pg_trigger</structname> catalog
</entry>
</row>
<row>
<entry><structfield>relukeys</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Unused (<emphasis>not</emphasis> the number of unique keys)</entry>
</row>
<row>
<entry><structfield>relfkeys</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Unused (<emphasis>not</emphasis> the number of foreign keys on the table)</entry>
</row>
<row>
<entry><structfield>relrefs</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Unused</entry>
</row>
<row>
<entry><structfield>relhasoids</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
True if we generate an OID for each row of the relation
</entry>
</row>
<row>
<entry><structfield>relhaspkey</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
True if the table has (or once had) a primary key
</entry>
</row>
<row>
<entry><structfield>relhasrules</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if table has rules; see
<structname>pg_rewrite</structname> catalog
</entry>
</row>
<row>
<entry><structfield>relhassubclass</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if table has (or once had) any inheritance children</entry>
</row>
<row>
<entry><structfield>relminxid</structfield></entry>
<entry><type>xid</type></entry>
<entry></entry>
<entry>
The minimum transaction ID present in all rows in this table. This
value is used to determine the database-global
<structname>pg_database</>.<structfield>datminxid</> value.
</entry>
</row>
<row>
<entry><structfield>relvacuumxid</structfield></entry>
<entry><type>xid</type></entry>
<entry></entry>
<entry>
The transaction ID that was used as cleaning point as of the last vacuum
operation. All rows inserted, updated or deleted in this table by
transactions whose IDs are below this one have been marked as known good
or deleted. This is used to determine the database-global
<structname>pg_database</>.<structfield>datvacuumxid</> value.
</entry>
</row>
<row>
<entry><structfield>relacl</structfield></entry>
<entry><type>aclitem[]</type></entry>
<entry></entry>
<entry>
Access privileges; see
<xref linkend="sql-grant" endterm="sql-grant-title"> and
<xref linkend="sql-revoke" endterm="sql-revoke-title">
for details
</entry>
</row>
<row>
<entry><structfield>reloptions</structfield></entry>
<entry><type>text[]</type></entry>
<entry></entry>
<entry>
Access-method-specific options, as <quote>keyword=value</> strings
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-constraint">
<title><structname>pg_constraint</structname></title>
<indexterm zone="catalog-pg-constraint">
<primary>pg_constraint</primary>
</indexterm>
<para>
The catalog <structname>pg_constraint</structname> stores check, primary key, unique, and foreign
key constraints on tables. (Column constraints are not treated
specially. Every column constraint is equivalent to some table
constraint.) Not-null constraints are represented in the
<structname>pg_attribute</> catalog.
</para>
<para>
Check constraints on domains are stored here, too.
</para>
<table>
<title><structname>pg_constraint</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>conname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Constraint name (not necessarily unique!)</entry>
</row>
<row>
<entry><structfield>connamespace</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
<entry>
The OID of the namespace that contains this constraint
</entry>
</row>
<row>
<entry><structfield>contype</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
<literal>c</> = check constraint,
<literal>f</> = foreign key constraint,
<literal>p</> = primary key constraint,
<literal>u</> = unique constraint
</entry>
</row>
<row>
<entry><structfield>condeferrable</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Is the constraint deferrable?</entry>
</row>
<row>
<entry><structfield>condeferred</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Is the constraint deferred by default?</entry>
</row>
<row>
<entry><structfield>conrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The table this constraint is on; 0 if not a table constraint</entry>
</row>
<row>
<entry><structfield>contypid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>The domain this constraint is on; 0 if not a domain constraint</entry>
</row>
<row>
<entry><structfield>confrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>If a foreign key, the referenced table; else 0</entry>
</row>
<row>
<entry><structfield>confupdtype</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>Foreign key update action code</entry>
</row>
<row>
<entry><structfield>confdeltype</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>Foreign key deletion action code</entry>
</row>
<row>
<entry><structfield>confmatchtype</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>Foreign key match type</entry>
</row>
<row>
<entry><structfield>conkey</structfield></entry>
<entry><type>int2[]</type></entry>
<entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</></entry>
<entry>If a table constraint, list of columns which the constraint constrains</entry>
</row>
<row>
<entry><structfield>confkey</structfield></entry>
<entry><type>int2[]</type></entry>
<entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</></entry>
<entry>If a foreign key, list of the referenced columns</entry>
</row>
<row>
<entry><structfield>conbin</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>If a check constraint, an internal representation of the expression</entry>
</row>
<row>
<entry><structfield>consrc</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>If a check constraint, a human-readable representation of the expression</entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
<structfield>consrc</structfield> is not updated when referenced objects
change; for example, it won't track renaming of columns. Rather than
relying on this field, it's best to use <function>pg_get_constraintdef()</>
to extract the definition of a check constraint.
</para>
</note>
<note>
<para>
<literal>pg_class.relchecks</literal> needs to agree with the
number of check-constraint entries found in this table for the
given relation.
</para>
</note>
</sect1>
<sect1 id="catalog-pg-conversion">
<title><structname>pg_conversion</structname></title>
<indexterm zone="catalog-pg-conversion">
<primary>pg_conversion</primary>
</indexterm>
<para>
The catalog <structname>pg_conversion</structname> describes the
available encoding conversion procedures. See
<xref linkend="sql-createconversion" endterm="sql-createconversion-title">
for more information.
</para>
<table>
<title><structname>pg_conversion</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>conname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Conversion name (unique within a namespace)</entry>
</row>
<row>
<entry><structfield>connamespace</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
<entry>
The OID of the namespace that contains this conversion
</entry>
</row>
<row>
<entry><structfield>conowner</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>Owner of the conversion</entry>
</row>
<row>
<entry><structfield>conforencoding</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>Source encoding ID</entry>
</row>
<row>
<entry><structfield>contoencoding</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>Destination encoding ID</entry>
</row>
<row>
<entry><structfield>conproc</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Conversion procedure</entry>
</row>
<row>
<entry><structfield>condefault</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if this is the default conversion</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-database">
<title><structname>pg_database</structname></title>
<indexterm zone="catalog-pg-database">
<primary>pg_database</primary>
</indexterm>
<para>
The catalog <structname>pg_database</structname> stores information
about the available databases. Databases are created with the
<command>CREATE DATABASE</command> command. Consult
<xref linkend="managing-databases"> for details about the meaning of some of the
parameters.
</para>
<para>
Unlike most system catalogs, <structname>pg_database</structname>
is shared across all databases of a cluster: there is only one
copy of <structname>pg_database</structname> per cluster, not
one per database.
</para>
<table>
<title><structname>pg_database</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>datname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Database name</entry>
</row>
<row>
<entry><structfield>datdba</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>Owner of the database, usually the user who created it</entry>
</row>
<row>
<entry><structfield>encoding</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>Character encoding for this database
(<function>pg_encoding_to_char()</function> can translate
this number to the encoding name)</entry>
</row>
<row>
<entry><structfield>datistemplate</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
If true then this database can be used in the
<literal>TEMPLATE</literal> clause of <command>CREATE
DATABASE</command> to create a new database as a clone of
this one.
</entry>
</row>
<row>
<entry><structfield>datallowconn</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
If false then no one can connect to this database. This is
used to protect the <literal>template0</> database from being altered.
</entry>
</row>
<row>
<entry><structfield>datconnlimit</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
Sets maximum number of concurrent connections that can be made
to this database. -1 means no limit.
</entry>
</row>
<row>
<entry><structfield>datlastsysoid</structfield></entry>
<entry><type>oid</type></entry>
<entry></entry>
<entry>
Last system OID in the database; useful
particularly to <application>pg_dump</application>
</entry>
</row>
<row>
<entry><structfield>datvacuumxid</structfield></entry>
<entry><type>xid</type></entry>
<entry></entry>
<entry>
The transaction ID that was used as cleaning point as of the last vacuum
operation. All rows inserted or deleted by transaction IDs before this one
have been marked as known good or deleted. This
is used to determine when commit-log space can be recycled.
If InvalidTransactionId, then the minimum is unknown and can be
determined by scanning <structname>pg_class</>.<structfield>relvacuumxid</>.
</entry>
</row>
<row>
<entry><structfield>datminxid</structfield></entry>
<entry><type>xid</type></entry>
<entry></entry>
<entry>
The minimum transaction ID present in all tables in this database.
All rows inserted by transaction IDs before this one have been
relabeled with a permanent (<quote>frozen</>) transaction ID in this
database. This is useful to check whether a database must be
vacuumed soon to avoid transaction ID wrap-around problems.
If InvalidTransactionId, then the minimum is unknown and can be
determined by scanning <structname>pg_class</>.<structfield>relminxid</>.
</entry>
</row>
<row>
<entry><structfield>dattablespace</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.oid</literal></entry>
<entry>
The default tablespace for the database.
Within this database, all tables for which
<structname>pg_class</>.<structfield>reltablespace</> is zero
will be stored in this tablespace; in particular, all the non-shared
system catalogs will be there.
</entry>
</row>
<row>
<entry><structfield>datconfig</structfield></entry>
<entry><type>text[]</type></entry>
<entry></entry>
<entry>Session defaults for run-time configuration variables</entry>
</row>
<row>
<entry><structfield>datacl</structfield></entry>
<entry><type>aclitem[]</type></entry>
<entry></entry>
<entry>
Access privileges; see
<xref linkend="sql-grant" endterm="sql-grant-title"> and
<xref linkend="sql-revoke" endterm="sql-revoke-title">
for details
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-depend">
<title><structname>pg_depend</structname></title>
<indexterm zone="catalog-pg-depend">
<primary>pg_depend</primary>
</indexterm>
<para>
The catalog <structname>pg_depend</structname> records the dependency
relationships between database objects. This information allows
<command>DROP</> commands to find which other objects must be dropped
by <command>DROP CASCADE</> or prevent dropping in the <command>DROP
RESTRICT</> case.
</para>
<para>
See also <link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link>,
which performs a similar function for dependencies involving objects
that are shared across a database cluster.
</para>
<table>
<title><structname>pg_depend</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>classid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The OID of the system catalog the dependent object is in</entry>
</row>
<row>
<entry><structfield>objid</structfield></entry>
<entry><type>oid</type></entry>
<entry>any OID column</entry>
<entry>The OID of the specific dependent object</entry>
</row>
<row>
<entry><structfield>objsubid</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
For a table column, this is the column number (the
<structfield>objid</> and <structfield>classid</> refer to the
table itself). For all other object types, this column is
zero.
</entry>
</row>
<row>
<entry><structfield>refclassid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The OID of the system catalog the referenced object is in</entry>
</row>
<row>
<entry><structfield>refobjid</structfield></entry>
<entry><type>oid</type></entry>
<entry>any OID column</entry>
<entry>The OID of the specific referenced object</entry>
</row>
<row>
<entry><structfield>refobjsubid</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
For a table column, this is the column number (the
<structfield>refobjid</> and <structfield>refclassid</> refer
to the table itself). For all other object types, this column
is zero.
</entry>
</row>
<row>
<entry><structfield>deptype</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
A code defining the specific semantics of this dependency relationship; see text
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
In all cases, a <structname>pg_depend</structname> entry indicates that the
referenced object may not be dropped without also dropping the dependent
object. However, there are several subflavors identified by
<structfield>deptype</>:
<variablelist>
<varlistentry>
<term><symbol>DEPENDENCY_NORMAL</> (<literal>n</>)</term>
<listitem>
<para>
A normal relationship between separately-created objects. The
dependent object may be dropped without affecting the
referenced object. The referenced object may only be dropped
by specifying <literal>CASCADE</>, in which case the dependent
object is dropped, too. Example: a table column has a normal
dependency on its data type.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><symbol>DEPENDENCY_AUTO</> (<literal>a</>)</term>
<listitem>
<para>
The dependent object can be dropped separately from the
referenced object, and should be automatically dropped
(regardless of <literal>RESTRICT</> or <literal>CASCADE</>
mode) if the referenced object is dropped. Example: a named
constraint on a table is made autodependent on the table, so
that it will go away if the table is dropped.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><symbol>DEPENDENCY_INTERNAL</> (<literal>i</>)</term>
<listitem>
<para>
The dependent object was created as part of creation of the
referenced object, and is really just a part of its internal
implementation. A <command>DROP</> of the dependent object
will be disallowed outright (we'll tell the user to issue a
<command>DROP</> against the referenced object, instead). A
<command>DROP</> of the referenced object will be propagated
through to drop the dependent object whether
<command>CASCADE</> is specified or not. Example: a trigger
that's created to enforce a foreign-key constraint is made
internally dependent on the constraint's
<structname>pg_constraint</> entry.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><symbol>DEPENDENCY_PIN</> (<literal>p</>)</term>
<listitem>
<para>
There is no dependent object; this type of entry is a signal
that the system itself depends on the referenced object, and so
that object must never be deleted. Entries of this type are
created only by <command>initdb</command>. The columns for the
dependent object contain zeroes.
</para>
</listitem>
</varlistentry>
</variablelist>
Other dependency flavors may be needed in future.
</para>
</sect1>
<sect1 id="catalog-pg-description">
<title><structname>pg_description</structname></title>
<indexterm zone="catalog-pg-description">
<primary>pg_description</primary>
</indexterm>
<para>
The catalog <structname>pg_description</> stores optional descriptions
(comments) for each database object. Descriptions can be manipulated
with the <command>COMMENT</command> command and viewed with
<application>psql</application>'s <literal>\d</literal> commands.
Descriptions of many built-in system objects are provided in the initial
contents of <structname>pg_description</structname>.
</para>
<para>
See also <link linkend="catalog-pg-shdescription"><structname>pg_shdescription</structname></link>,
which performs a similar function for descriptions involving objects that
are shared across a database cluster.
</para>
<table>
<title><structname>pg_description</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>objoid</structfield></entry>
<entry><type>oid</type></entry>
<entry>any OID column</entry>
<entry>The OID of the object this description pertains to</entry>
</row>
<row>
<entry><structfield>classoid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The OID of the system catalog this object appears in</entry>
</row>
<row>
<entry><structfield>objsubid</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
For a comment on a table column, this is the column number (the
<structfield>objoid</> and <structfield>classoid</> refer to
the table itself). For all other object types, this column is
zero.
</entry>
</row>
<row>
<entry><structfield>description</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Arbitrary text that serves as the description of this object</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-index">
<title><structname>pg_index</structname></title>
<indexterm zone="catalog-pg-index">
<primary>pg_index</primary>
</indexterm>
<para>
The catalog <structname>pg_index</structname> contains part of the information
about indexes. The rest is mostly in
<structname>pg_class</structname>.
</para>
<table>
<title><structname>pg_index</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>indexrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The OID of the <structname>pg_class</> entry for this index</entry>
</row>
<row>
<entry><structfield>indrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The OID of the <structname>pg_class</> entry for the table this index is for</entry>
</row>
<row>
<entry><structfield>indnatts</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>The number of columns in the index (duplicates
<literal>pg_class.relnatts</literal>)</entry>
</row>
<row>
<entry><structfield>indisunique</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>If true, this is a unique index</entry>
</row>
<row>
<entry><structfield>indisprimary</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>If true, this index represents the primary key of the table.
(<structfield>indisunique</> should always be true when this is true.)</entry>
</row>
<row>
<entry><structfield>indisclustered</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>If true, the table was last clustered on this index</entry>
</row>
<row>
<entry><structfield>indisvalid</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>If true, the index is currently valid for queries.
False means the index is possibly incomplete: it must still be
inserted into by INSERT/UPDATE operations, but it cannot safely be
used for queries, and if it is unique, the uniqueness shouldn't be
relied on either.</entry>
</row>
<row>
<entry><structfield>indkey</structfield></entry>
<entry><type>int2vector</type></entry>
<entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry>
<entry>
This is an array of <structfield>indnatts</structfield> values that
indicate which table columns this index indexes. For example a value
of <literal>1 3</literal> would mean that the first and the third table
columns make up the index key. A zero in this array indicates that the
corresponding index attribute is an expression over the table columns,
rather than a simple column reference.
</entry>
</row>
<row>
<entry><structfield>indclass</structfield></entry>
<entry><type>oidvector</type></entry>
<entry><literal><link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.oid</literal></entry>
<entry>
For each column in the index key this contains the OID of
the operator class to use. See
<structname>pg_opclass</structname> for details.
</entry>
</row>
<row>
<entry><structfield>indexprs</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Expression trees (in <function>nodeToString()</function> representation)
for index attributes that are not simple column references. This is a
list with one element for each zero entry in <structfield>indkey</>.
NULL if all index attributes are simple references.</entry>
</row>
<row>
<entry><structfield>indpred</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Expression tree (in <function>nodeToString()</function> representation)
for partial index predicate. NULL if not a partial index.</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-inherits">
<title><structname>pg_inherits</structname></title>
<indexterm zone="catalog-pg-inherits">
<primary>pg_inherits</primary>
</indexterm>
<para>
The catalog <structname>pg_inherits</> records information about
table inheritance hierarchies. There is one entry for each direct
child table in the database. (Indirect inheritance can be determined
by following chains of entries.)
</para>
<table>
<title><structname>pg_inherits</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>inhrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>
The OID of the child table
</entry>
</row>
<row>
<entry><structfield>inhparent</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>
The OID of the parent table
</entry>
</row>
<row>
<entry><structfield>inhseqno</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
If there is more than one direct parent for a child table (multiple
inheritance), this number tells the order in which the
inherited columns are to be arranged. The count starts at 1.
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-language">
<title><structname>pg_language</structname></title>
<indexterm zone="catalog-pg-language">
<primary>pg_language</primary>
</indexterm>
<para>
The catalog <structname>pg_language</structname> registers
languages in which you can write functions or stored procedures.
See <xref linkend="sql-createlanguage" endterm="sql-createlanguage-title">
and <xref linkend="xplang"> for more information about language handlers.
</para>
<table>
<title><structname>pg_language</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>lanname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Name of the language</entry>
</row>
<row>
<entry><structfield>lanispl</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
This is false for internal languages (such as
<acronym>SQL</acronym>) and true for user-defined languages.
Currently, <application>pg_dump</application> still uses this
to determine which languages need to be dumped, but this may be
replaced by a different mechanism sometime.
</entry>
</row>
<row>
<entry><structfield>lanpltrusted</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
True if this is a trusted language, which means that it is believed
not to grant access to anything outside the normal SQL execution
environment. Only superusers may create functions in untrusted
languages.
</entry>
</row>
<row>
<entry><structfield>lanplcallfoid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>
For noninternal languages this references the language
handler, which is a special function that is responsible for
executing all functions that are written in the particular
language.
</entry>
</row>
<row>
<entry><structfield>lanvalidator</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>
This references a language validator function that is responsible
for checking the syntax and validity of new functions when they
are created. Zero if no validator is provided.
</entry>
</row>
<row>
<entry><structfield>lanacl</structfield></entry>
<entry><type>aclitem[]</type></entry>
<entry></entry>
<entry>
Access privileges; see
<xref linkend="sql-grant" endterm="sql-grant-title"> and
<xref linkend="sql-revoke" endterm="sql-revoke-title">
for details
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-largeobject">
<title><structname>pg_largeobject</structname></title>
<indexterm zone="catalog-pg-largeobject">
<primary>pg_largeobject</primary>
</indexterm>
<para>
The catalog <structname>pg_largeobject</structname> holds the data making up
<quote>large objects</quote>. A large object is identified by an
OID assigned when it is created. Each large object is broken into
segments or <quote>pages</> small enough to be conveniently stored as rows
in <structname>pg_largeobject</structname>.
The amount of data per page is defined to be <literal>LOBLKSIZE</> (which is currently
<literal>BLCKSZ/4</>, or typically 2 kB).
</para>
<table>
<title><structname>pg_largeobject</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>loid</structfield></entry>
<entry><type>oid</type></entry>
<entry></entry>
<entry>Identifier of the large object that includes this page</entry>
</row>
<row>
<entry><structfield>pageno</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>Page number of this page within its large object
(counting from zero)</entry>
</row>
<row>
<entry><structfield>data</structfield></entry>
<entry><type>bytea</type></entry>
<entry></entry>
<entry>
Actual data stored in the large object.
This will never be more than <symbol>LOBLKSIZE</> bytes and may be less.
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Each row of <structname>pg_largeobject</structname> holds data
for one page of a large object, beginning at
byte offset (<literal>pageno * LOBLKSIZE</>) within the object. The implementation
allows sparse storage: pages may be missing, and may be shorter than
<literal>LOBLKSIZE</> bytes even if they are not the last page of the object.
Missing regions within a large object read as zeroes.
</para>
</sect1>
<sect1 id="catalog-pg-listener">
<title><structname>pg_listener</structname></title>
<indexterm zone="catalog-pg-listener">
<primary>pg_listener</primary>
</indexterm>
<para>
The catalog <structname>pg_listener</structname> supports the
<xref linkend="sql-listen" endterm="sql-listen-title"> and
<xref linkend="sql-notify" endterm="sql-notify-title">
commands. A listener creates an entry in
<structname>pg_listener</structname> for each notification name
it is listening for. A notifier scans <structname>pg_listener</structname>
and updates each matching entry to show that a notification has occurred.
The notifier also sends a signal (using the PID recorded in the table)
to awaken the listener from sleep.
</para>
<table>
<title><structname>pg_listener</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>relname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Notify condition name. (The name need not match any actual
relation in the database; the name <structfield>relname</> is historical.)
</entry>
</row>
<row>
<entry><structfield>listenerpid</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>PID of the server process that created this entry</entry>
</row>
<row>
<entry><structfield>notification</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
Zero if no event is pending for this listener. If an event is
pending, the PID of the server process that sent the notification.
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-namespace">
<title><structname>pg_namespace</structname></title>
<indexterm zone="catalog-pg-namespace">
<primary>pg_namespace</primary>
</indexterm>
<para>
The catalog <structname>pg_namespace</> stores namespaces.
A namespace is the structure underlying SQL schemas: each namespace
can have a separate collection of relations, types, etc. without name
conflicts.
</para>
<table>
<title><structname>pg_namespace</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>nspname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Name of the namespace</entry>
</row>
<row>
<entry><structfield>nspowner</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>Owner of the namespace</entry>
</row>
<row>
<entry><structfield>nspacl</structfield></entry>
<entry><type>aclitem[]</type></entry>
<entry></entry>
<entry>
Access privileges; see
<xref linkend="sql-grant" endterm="sql-grant-title"> and
<xref linkend="sql-revoke" endterm="sql-revoke-title">
for details
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-opclass">
<title><structname>pg_opclass</structname></title>
<indexterm zone="catalog-pg-opclass">
<primary>pg_opclass</primary>
</indexterm>
<para>
The catalog <structname>pg_opclass</structname> defines
index access method operator classes. Each operator class defines
semantics for index columns of a particular data type and a particular
index access method. Note that there can be multiple operator classes
for a given data type/access method combination, thus supporting multiple
behaviors.
</para>
<para>
Operator classes are described at length in <xref linkend="xindex">.
</para>
<table>
<title><structname>pg_opclass</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>opcamid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
<entry>Index access method operator class is for</entry>
</row>
<row>
<entry><structfield>opcname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Name of this operator class</entry>
</row>
<row>
<entry><structfield>opcnamespace</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
<entry>Namespace of this operator class</entry>
</row>
<row>
<entry><structfield>opcowner</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>Owner of the operator class</entry>
</row>
<row>
<entry><structfield>opcintype</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>Data type that the operator class indexes</entry>
</row>
<row>
<entry><structfield>opcdefault</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if this operator class is the default for <structfield>opcintype</></entry>
</row>
<row>
<entry><structfield>opckeytype</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>Type of data stored in index, or zero if same as <structfield>opcintype</></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The majority of the information defining an operator class is actually
not in its <structname>pg_opclass</structname> row, but in the associated
rows in <structname>pg_amop</structname> and
<structname>pg_amproc</structname>. Those rows are considered to be
part of the operator class definition &mdash; this is not unlike the way
that a relation is defined by a single <structname>pg_class</structname>
row plus associated rows in <structname>pg_attribute</structname> and
other tables.
</para>
</sect1>
<sect1 id="catalog-pg-operator">
<title><structname>pg_operator</structname></title>
<indexterm zone="catalog-pg-operator">
<primary>pg_operator</primary>
</indexterm>
<para>
The catalog <structname>pg_operator</> stores information about operators.
See <xref linkend="sql-createoperator" endterm="sql-createoperator-title">
and <xref linkend="xoper"> for more information.
</para>
<table>
<title><structname>pg_operator</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>oprname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Name of the operator</entry>
</row>
<row>
<entry><structfield>oprnamespace</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
<entry>
The OID of the namespace that contains this operator
</entry>
</row>
<row>
<entry><structfield>oprowner</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>Owner of the operator</entry>
</row>
<row>
<entry><structfield>oprkind</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
<literal>b</> = infix (<quote>both</quote>), <literal>l</> = prefix
(<quote>left</quote>), <literal>r</> = postfix (<quote>right</quote>)
</entry>
</row>
<row>
<entry><structfield>oprcanhash</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>This operator supports hash joins</entry>
</row>
<row>
<entry><structfield>oprleft</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>Type of the left operand</entry>
</row>
<row>
<entry><structfield>oprright</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>Type of the right operand</entry>
</row>
<row>
<entry><structfield>oprresult</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>Type of the result</entry>
</row>
<row>
<entry><structfield>oprcom</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
<entry>Commutator of this operator, if any</entry>
</row>
<row>
<entry><structfield>oprnegate</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
<entry>Negator of this operator, if any</entry>
</row>
<row>
<entry><structfield>oprlsortop</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
<entry>
If this operator supports merge joins, the operator that sorts
the type of the left-hand operand (<literal>L&lt;L</>)
</entry>
</row>
<row>
<entry><structfield>oprrsortop</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
<entry>
If this operator supports merge joins, the operator that sorts
the type of the right-hand operand (<literal>R&lt;R</>)
</entry>
</row>
<row>
<entry><structfield>oprltcmpop</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
<entry>
If this operator supports merge joins, the less-than operator that
compares the left and right operand types (<literal>L&lt;R</>)
</entry>
</row>
<row>
<entry><structfield>oprgtcmpop</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
<entry>
If this operator supports merge joins, the greater-than operator that
compares the left and right operand types (<literal>L&gt;R</>)
</entry>
</row>
<row>
<entry><structfield>oprcode</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Function that implements this operator</entry>
</row>
<row>
<entry><structfield>oprrest</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Restriction selectivity estimation function for this operator</entry>
</row>
<row>
<entry><structfield>oprjoin</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Join selectivity estimation function for this operator</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Unused column contain zeroes. For example, <structfield>oprleft</structfield>
is zero for a prefix operator.
</para>
</sect1>
<sect1 id="catalog-pg-pltemplate">
<title><structname>pg_pltemplate</structname></title>
<indexterm zone="catalog-pg-pltemplate">
<primary>pg_pltemplate</primary>
</indexterm>
<para>
The catalog <structname>pg_pltemplate</structname> stores
<quote>template</> information for procedural languages.
A template for a language allows the language to be created in a
particular database by a simple <command>CREATE LANGUAGE</> command,
with no need to specify implementation details.
</para>
<para>
Unlike most system catalogs, <structname>pg_pltemplate</structname>
is shared across all databases of a cluster: there is only one
copy of <structname>pg_pltemplate</structname> per cluster, not
one per database. This allows the information to be accessible in
each database as it is needed.
</para>
<table>
<title><structname>pg_pltemplate</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>tmplname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Name of the language this template is for</entry>
</row>
<row>
<entry><structfield>tmpltrusted</structfield></entry>
<entry><type>boolean</type></entry>
<entry></entry>
<entry>True if language is considered trusted</entry>
</row>
<row>
<entry><structfield>tmplhandler</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Name of call handler function</entry>
</row>
<row>
<entry><structfield>tmplvalidator</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Name of validator function, or NULL if none</entry>
</row>
<row>
<entry><structfield>tmpllibrary</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Path of shared library that implements language</entry>
</row>
<row>
<entry><structfield>tmplacl</structfield></entry>
<entry><type>aclitem[]</type></entry>
<entry></entry>
<entry>Access privileges for template (not yet used)</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
There are not currently any commands that manipulate procedural language
templates; to change the built-in information, a superuser must modify
the table using ordinary <command>INSERT</command>, <command>DELETE</command>,
or <command>UPDATE</command> commands. It is likely that a future
release of <productname>PostgreSQL</productname> will offer
commands to change the entries in a cleaner fashion.
</para>
<para>
When implemented, the <structfield>tmplacl</structfield> field will provide
access control for the template itself (i.e., the right to create a
language using it), not for the languages created from the template.
</para>
</sect1>
<sect1 id="catalog-pg-proc">
<title><structname>pg_proc</structname></title>
<indexterm zone="catalog-pg-proc">
<primary>pg_proc</primary>
</indexterm>
<para>
The catalog <structname>pg_proc</> stores information about functions (or procedures).
See <xref linkend="sql-createfunction" endterm="sql-createfunction-title">
and <xref linkend="xfunc"> for more information.
</para>
<para>
The table contains data for aggregate functions as well as plain functions.
If <structfield>proisagg</structfield> is true, there should be a matching
row in <structfield>pg_aggregate</structfield>.
</para>
<table>
<title><structname>pg_proc</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>proname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Name of the function</entry>
</row>
<row>
<entry><structfield>pronamespace</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
<entry>
The OID of the namespace that contains this function
</entry>
</row>
<row>
<entry><structfield>proowner</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>Owner of the function</entry>
</row>
<row>
<entry><structfield>prolang</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-language"><structname>pg_language</structname></link>.oid</literal></entry>
<entry>Implementation language or call interface of this function</entry>
</row>
<row>
<entry><structfield>proisagg</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Function is an aggregate function</entry>
</row>
<row>
<entry><structfield>prosecdef</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Function is a security definer (i.e., a <quote>setuid</>
function)</entry>
</row>
<row>
<entry><structfield>proisstrict</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
Function returns null if any call argument is null. In that
case the function won't actually be called at all. Functions
that are not <quote>strict</quote> must be prepared to handle
null inputs.
</entry>
</row>
<row>
<entry><structfield>proretset</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Function returns a set (i.e., multiple values of the specified
data type)</entry>
</row>
<row>
<entry><structfield>provolatile</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
<structfield>provolatile</structfield> tells whether the function's
result depends only on its input arguments, or is affected by outside
factors.
It is <literal>i</literal> for <quote>immutable</> functions,
which always deliver the same result for the same inputs.
It is <literal>s</literal> for <quote>stable</> functions,
whose results (for fixed inputs) do not change within a scan.
It is <literal>v</literal> for <quote>volatile</> functions,
whose results may change at any time. (Use <literal>v</literal> also
for functions with side-effects, so that calls to them cannot get
optimized away.)
</entry>
</row>
<row>
<entry><structfield>pronargs</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Number of arguments</entry>
</row>
<row>
<entry><structfield>prorettype</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>Data type of the return value</entry>
</row>
<row>
<entry><structfield>proargtypes</structfield></entry>
<entry><type>oidvector</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>
An array with the data types of the function arguments. This includes
only input arguments (including INOUT arguments), and thus represents
the call signature of the function.
</entry>
</row>
<row>
<entry><structfield>proallargtypes</structfield></entry>
<entry><type>oid[]</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>
An array with the data types of the function arguments. This includes
all arguments (including OUT and INOUT arguments); however, if all the
arguments are IN arguments, this field will be null.
Note that subscripting is 1-based, whereas for historical reasons
<structfield>proargtypes</> is subscripted from 0.
</entry>
</row>
<row>
<entry><structfield>proargmodes</structfield></entry>
<entry><type>char[]</type></entry>
<entry></entry>
<entry>
An array with the modes of the function arguments, encoded as
<literal>i</literal> for IN arguments,
<literal>o</literal> for OUT arguments,
<literal>b</literal> for INOUT arguments.
If all the arguments are IN arguments, this field will be null.
Note that subscripts correspond to positions of
<structfield>proallargtypes</> not <structfield>proargtypes</>.
</entry>
</row>
<row>
<entry><structfield>proargnames</structfield></entry>
<entry><type>text[]</type></entry>
<entry></entry>
<entry>
An array with the names of the function arguments.
Arguments without a name are set to empty strings in the array.
If none of the arguments have a name, this field will be null.
Note that subscripts correspond to positions of
<structfield>proallargtypes</> not <structfield>proargtypes</>.
</entry>
</row>
<row>
<entry><structfield>prosrc</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>
This tells the function handler how to invoke the function. It
might be the actual source code of the function for interpreted
languages, a link symbol, a file name, or just about anything
else, depending on the implementation language/call convention.
</entry>
</row>
<row>
<entry><structfield>probin</structfield></entry>
<entry><type>bytea</type></entry>
<entry></entry>
<entry>Additional information about how to invoke the function.
Again, the interpretation is language-specific.
</entry>
</row>
<row>
<entry><structfield>proacl</structfield></entry>
<entry><type>aclitem[]</type></entry>
<entry></entry>
<entry>
Access privileges; see
<xref linkend="sql-grant" endterm="sql-grant-title"> and
<xref linkend="sql-revoke" endterm="sql-revoke-title">
for details
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
For compiled functions, both built-in and dynamically loaded,
<structfield>prosrc</structfield> contains the function's C-language
name (link symbol). For all other currently-known language types,
<structfield>prosrc</structfield> contains the function's source
text. <structfield>probin</structfield> is unused except for
dynamically-loaded C functions, for which it gives the name of the
shared library file containing the function.
</para>
</sect1>
<sect1 id="catalog-pg-rewrite">
<title><structname>pg_rewrite</structname></title>
<indexterm zone="catalog-pg-rewrite">
<primary>pg_rewrite</primary>
</indexterm>
<para>
The catalog <structname>pg_rewrite</structname> stores rewrite rules for tables and views.
</para>
<table>
<title><structname>pg_rewrite</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>rulename</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Rule name</entry>
</row>
<row>
<entry><structfield>ev_class</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The table this rule is for</entry>
</row>
<row>
<entry><structfield>ev_attr</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>The column this rule is for (currently, always zero to
indicate the whole table)</entry>
</row>
<row>
<entry><structfield>ev_type</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
Event type that the rule is for: 1 = <command>SELECT</>, 2 =
<command>UPDATE</>, 3 = <command>INSERT</>, 4 =
<command>DELETE</>
</entry>
</row>
<row>
<entry><structfield>is_instead</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if the rule is an <literal>INSTEAD</literal> rule</entry>
</row>
<row>
<entry><structfield>ev_qual</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>
Expression tree (in the form of a
<function>nodeToString()</function> representation) for the
rule's qualifying condition
</entry>
</row>
<row>
<entry><structfield>ev_action</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>
Query tree (in the form of a
<function>nodeToString()</function> representation) for the
rule's action
</entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
<literal>pg_class.relhasrules</literal>
must be true if a table has any rules in this catalog.
</para>
</note>
</sect1>
<sect1 id="catalog-pg-shdepend">
<title><structname>pg_shdepend</structname></title>
<indexterm zone="catalog-pg-shdepend">
<primary>pg_shdepend</primary>
</indexterm>
<para>
The catalog <structname>pg_shdepend</structname> records the
dependency relationships between database objects and shared objects,
such as roles. This information allows
<productname>PostgreSQL</productname> to ensure that those objects are
unreferenced before attempting to delete them.
</para>
<para>
See also <link linkend="catalog-pg-depend"><structname>pg_depend</structname></link>,
which performs a similar function for dependencies involving objects
within a single database.
</para>
<para>
Unlike most system catalogs, <structname>pg_shdepend</structname>
is shared across all databases of a cluster: there is only one
copy of <structname>pg_shdepend</structname> per cluster, not
one per database.
</para>
<table>
<title><structname>pg_shdepend</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>dbid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.oid</literal></entry>
<entry>The OID of the database the dependent object is in,
or zero for a shared object</entry>
</row>
<row>
<entry><structfield>classid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The OID of the system catalog the dependent object is in</entry>
</row>
<row>
<entry><structfield>objid</structfield></entry>
<entry><type>oid</type></entry>
<entry>any OID column</entry>
<entry>The OID of the specific dependent object</entry>
</row>
<row>
<entry><structfield>refclassid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The OID of the system catalog the referenced object is in
(must be a shared catalog)</entry>
</row>
<row>
<entry><structfield>refobjid</structfield></entry>
<entry><type>oid</type></entry>
<entry>any OID column</entry>
<entry>The OID of the specific referenced object</entry>
</row>
<row>
<entry><structfield>deptype</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
A code defining the specific semantics of this dependency relationship; see text
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
In all cases, a <structname>pg_shdepend</structname> entry indicates that
the referenced object may not be dropped without also dropping the dependent
object. However, there are several subflavors identified by
<structfield>deptype</>:
<variablelist>
<varlistentry>
<term><symbol>SHARED_DEPENDENCY_OWNER</> (<literal>o</>)</term>
<listitem>
<para>
The referenced object (which must be a role) is the owner of the
dependent object.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><symbol>SHARED_DEPENDENCY_ACL</> (<literal>a</>)</term>
<listitem>
<para>
The referenced object (which must be a role) is mentioned in the
ACL (access control list, i.e., privileges list) of the
dependent object. (A <symbol>SHARED_DEPENDENCY_ACL</> entry is
not made for the owner of the object, since the owner will have
a <symbol>SHARED_DEPENDENCY_OWNER</> entry anyway.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><symbol>SHARED_DEPENDENCY_PIN</> (<literal>p</>)</term>
<listitem>
<para>
There is no dependent object; this type of entry is a signal
that the system itself depends on the referenced object, and so
that object must never be deleted. Entries of this type are
created only by <command>initdb</command>. The columns for the
dependent object contain zeroes.
</para>
</listitem>
</varlistentry>
</variablelist>
Other dependency flavors may be needed in future. Note in particular
that the current definition only supports roles as referenced objects.
</para>
</sect1>
<sect1 id="catalog-pg-shdescription">
<title><structname>pg_shdescription</structname></title>
<indexterm zone="catalog-pg-shdescription">
<primary>pg_shdescription</primary>
</indexterm>
<para>
The catalog <structname>pg_shdescription</structname> stores optional
descriptions (comments) for shared database objects. Descriptions can
be manipulated with the <command>COMMENT</command> command and viewed
with <application>psql</application>'s <literal>\d</literal> commands.
</para>
<para>
See also <link linkend="catalog-pg-description"><structname>pg_description</structname></link>,
which performs a similar function for descriptions involving objects
within a single database.
</para>
<para>
Unlike most system catalogs, <structname>pg_shdescription</structname>
is shared across all databases of a cluster: there is only one
copy of <structname>pg_shdescription</structname> per cluster, not
one per database.
</para>
<table>
<title><structname>pg_shdescription</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>objoid</structfield></entry>
<entry><type>oid</type></entry>
<entry>any OID column</entry>
<entry>The OID of the object this description pertains to</entry>
</row>
<row>
<entry><structfield>classoid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The OID of the system catalog this object appears in</entry>
</row>
<row>
<entry><structfield>description</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Arbitrary text that servers as the description of this object.</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-statistic">
<title><structname>pg_statistic</structname></title>
<indexterm zone="catalog-pg-statistic">
<primary>pg_statistic</primary>
</indexterm>
<para>
The catalog <structname>pg_statistic</structname> stores statistical data
about the contents of the database. Entries are created by
<command>ANALYZE</command> and subsequently used by the query planner.
There is one entry for each table column that has been analyzed.
Note that all the statistical data is inherently approximate,
even assuming that it is up-to-date.
</para>
<para>
<structname>pg_statistic</structname> also stores statistical data about
the values of index expressions. These are described as if they were
actual data columns; in particular, <structfield>starelid</structfield>
references the index. No entry is made for an ordinary non-expression
index column, however, since it would be redundant with the entry
for the underlying table column.
</para>
<para>
Since different kinds of statistics may be appropriate for different
kinds of data, <structname>pg_statistic</structname> is designed not
to assume very much about what sort of statistics it stores. Only
extremely general statistics (such as nullness) are given dedicated
columns in <structname>pg_statistic</structname>. Everything else
is stored in <quote>slots</quote>, which are groups of associated columns
whose content is identified by a code number in one of the slot's columns.
For more information see
<filename>src/include/catalog/pg_statistic.h</filename>.
</para>
<para>
<structname>pg_statistic</structname> should not be readable by the
public, since even statistical information about a table's contents
may be considered sensitive. (Example: minimum and maximum values
of a salary column might be quite interesting.)
<link linkend="view-pg-stats"><structname>pg_stats</structname></link>
is a publicly readable view on
<structname>pg_statistic</structname> that only exposes information
about those tables that are readable by the current user.
</para>
<table>
<title><structname>pg_statistic</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>starelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The table or index that the described column belongs to</entry>
</row>
<row>
<entry><structfield>staattnum</structfield></entry>
<entry><type>int2</type></entry>
<entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry>
<entry>The number of the described column</entry>
</row>
<row>
<entry><structfield>stanullfrac</structfield></entry>
<entry><type>float4</type></entry>
<entry></entry>
<entry>The fraction of the column's entries that are null</entry>
</row>
<row>
<entry><structfield>stawidth</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>The average stored width, in bytes, of nonnull entries</entry>
</row>
<row>
<entry><structfield>stadistinct</structfield></entry>
<entry><type>float4</type></entry>
<entry></entry>
<entry>The number of distinct nonnull data values in the column.
A value greater than zero is the actual number of distinct values.
A value less than zero is the negative of a fraction of the number
of rows in the table (for example, a column in which values appear about
twice on the average could be represented by <structfield>stadistinct</> = -0.5).
A zero value means the number of distinct values is unknown.
</entry>
</row>
<row>
<entry><structfield>stakind<replaceable>N</></structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>
A code number indicating the kind of statistics stored in the
<replaceable>N</>th <quote>slot</quote> of the
<structname>pg_statistic</structname> row.
</entry>
</row>
<row>
<entry><structfield>staop<replaceable>N</></structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
<entry>
An operator used to derive the statistics stored in the
<replaceable>N</>th <quote>slot</quote>. For example, a
histogram slot would show the <literal>&lt;</literal> operator
that defines the sort order of the data.
</entry>
</row>
<row>
<entry><structfield>stanumbers<replaceable>N</></structfield></entry>
<entry><type>float4[]</type></entry>
<entry></entry>
<entry>
Numerical statistics of the appropriate kind for the
<replaceable>N</>th <quote>slot</quote>, or NULL if the slot
kind does not involve numerical values
</entry>
</row>
<row>
<entry><structfield>stavalues<replaceable>N</></structfield></entry>
<entry><type>anyarray</type></entry>
<entry></entry>
<entry>
Column data values of the appropriate kind for the
<replaceable>N</>th <quote>slot</quote>, or NULL if the slot
kind does not store any data values. Each array's element
values are actually of the specific column's data type, so there
is no way to define these columns' type more specifically than
<type>anyarray</>.
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-tablespace">
<title><structname>pg_tablespace</structname></title>
<indexterm zone="catalog-pg-tablespace">
<primary>pg_tablespace</primary>
</indexterm>
<para>
The catalog <structname>pg_tablespace</structname> stores information
about the available tablespaces. Tables can be placed in particular
tablespaces to aid administration of disk layout.
</para>
<para>
Unlike most system catalogs, <structname>pg_tablespace</structname>
is shared across all databases of a cluster: there is only one
copy of <structname>pg_tablespace</structname> per cluster, not
one per database.
</para>
<table>
<title><structname>pg_tablespace</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>spcname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Tablespace name</entry>
</row>
<row>
<entry><structfield>spcowner</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>Owner of the tablespace, usually the user who created it</entry>
</row>
<row>
<entry><structfield>spclocation</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Location (directory path) of the tablespace</entry>
</row>
<row>
<entry><structfield>spcacl</structfield></entry>
<entry><type>aclitem[]</type></entry>
<entry></entry>
<entry>
Access privileges; see
<xref linkend="sql-grant" endterm="sql-grant-title"> and
<xref linkend="sql-revoke" endterm="sql-revoke-title">
for details
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="catalog-pg-trigger">
<title><structname>pg_trigger</structname></title>
<indexterm zone="catalog-pg-trigger">
<primary>pg_trigger</primary>
</indexterm>
<para>
The catalog <structname>pg_trigger</structname> stores triggers on tables.
See <xref linkend="sql-createtrigger" endterm="sql-createtrigger-title">
for more information.
</para>
<table>
<title><structname>pg_trigger</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>tgrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The table this trigger is on</entry>
</row>
<row>
<entry><structfield>tgname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Trigger name (must be unique among triggers of same table)</entry>
</row>
<row>
<entry><structfield>tgfoid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>The function to be called</entry>
</row>
<row>
<entry><structfield>tgtype</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Bit mask identifying trigger conditions</entry>
</row>
<row>
<entry><structfield>tgenabled</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if trigger is enabled</entry>
</row>
<row>
<entry><structfield>tgisconstraint</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if trigger implements a referential integrity constraint</entry>
</row>
<row>
<entry><structfield>tgconstrname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Referential integrity constraint name</entry>
</row>
<row>
<entry><structfield>tgconstrrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The table referenced by an referential integrity constraint</entry>
</row>
<row>
<entry><structfield>tgdeferrable</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if deferrable</entry>
</row>
<row>
<entry><structfield>tginitdeferred</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>True if initially deferred</entry>
</row>
<row>
<entry><structfield>tgnargs</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Number of argument strings passed to trigger function</entry>
</row>
<row>
<entry><structfield>tgattr</structfield></entry>
<entry><type>int2vector</type></entry>
<entry></entry>
<entry>Currently unused</entry>
</row>
<row>
<entry><structfield>tgargs</structfield></entry>
<entry><type>bytea</type></entry>
<entry></entry>
<entry>Argument strings to pass to trigger, each NULL-terminated</entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
<literal>pg_class.reltriggers</literal> needs to agree with the
number of triggers found in this table for the given relation.
</para>
</note>
</sect1>
<sect1 id="catalog-pg-type">
<title><structname>pg_type</structname></title>
<indexterm zone="catalog-pg-type">
<primary>pg_type</primary>
</indexterm>
<para>
The catalog <structname>pg_type</structname> stores information about data
types. Base types (scalar types) are created with
<xref linkend="sql-createtype" endterm="sql-createtype-title">, and
domains with
<xref linkend="sql-createdomain" endterm="sql-createdomain-title">.
A composite type is automatically created for each table in the database, to
represent the row structure of the table. It is also possible to create
composite types with <command>CREATE TYPE AS</command>.
</para>
<table>
<title><structname>pg_type</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>typname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Data type name</entry>
</row>
<row>
<entry><structfield>typnamespace</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
<entry>
The OID of the namespace that contains this type
</entry>
</row>
<row>
<entry><structfield>typowner</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>Owner of the type</entry>
</row>
<row>
<entry><structfield>typlen</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>
For a fixed-size type, <structfield>typlen</structfield> is the number
of bytes in the internal representation of the type. But for a
variable-length type, <structfield>typlen</structfield> is negative.
-1 indicates a <quote>varlena</> type (one that has a length word),
-2 indicates a null-terminated C string.
</entry>
</row>
<row>
<entry><structfield>typbyval</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
<structfield>typbyval</structfield> determines whether internal
routines pass a value of this type by value or by reference.
<structfield>typbyval</structfield> had better be false if
<structfield>typlen</structfield> is not 1, 2, or 4 (or 8 on machines
where Datum is 8 bytes).
Variable-length types are always passed by reference. Note that
<structfield>typbyval</structfield> can be false even if the
length would allow pass-by-value; this is currently true for
type <type>float4</type>, for example.
</entry>
</row>
<row>
<entry><structfield>typtype</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>
<structfield>typtype</structfield> is <literal>b</literal> for
a base type, <literal>c</literal> for a composite type (e.g., a
table's row type), <literal>d</literal> for a domain, or
<literal>p</literal> for a pseudo-type. See also
<structfield>typrelid</structfield> and
<structfield>typbasetype</structfield>.
</entry>
</row>
<row>
<entry><structfield>typisdefined</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
True if the type is defined, false if this is a placeholder
entry for a not-yet-defined type. When
<structfield>typisdefined</structfield> is false, nothing
except the type name, namespace, and OID can be relied on.
</entry>
</row>
<row>
<entry><structfield>typdelim</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry>Character that separates two values of this type when parsing
array input. Note that the delimiter is associated with the array
element data type, not the array data type.</entry>
</row>
<row>
<entry><structfield>typrelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>
If this is a composite type (see
<structfield>typtype</structfield>), then this column points to
the <structname>pg_class</structname> entry that defines the
corresponding table. (For a free-standing composite type, the
<structname>pg_class</structname> entry doesn't really represent
a table, but it is needed anyway for the type's
<structname>pg_attribute</structname> entries to link to.)
Zero for non-composite types.
</entry>
</row>
<row>
<entry><structfield>typelem</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>
If <structfield>typelem</structfield> is not 0 then it
identifies another row in <structname>pg_type</structname>.
The current type can then be subscripted like an array yielding
values of type <structfield>typelem</structfield>. A
<quote>true</quote> array type is variable length
(<structfield>typlen</structfield> = -1),
but some fixed-length (<structfield>typlen</structfield> &gt; 0) types
also have nonzero <structfield>typelem</structfield>, for example
<type>name</type> and <type>point</type>.
If a fixed-length type has a <structfield>typelem</structfield> then
its internal representation must be some number of values of the
<structfield>typelem</structfield> data type with no other data.
Variable-length array types have a header defined by the array
subroutines.
</entry>
</row>
<row>
<entry><structfield>typinput</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Input conversion function (text format)</entry>
</row>
<row>
<entry><structfield>typoutput</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Output conversion function (text format)</entry>
</row>
<row>
<entry><structfield>typreceive</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Input conversion function (binary format), or 0 if none</entry>
</row>
<row>
<entry><structfield>typsend</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Output conversion function (binary format), or 0 if none</entry>
</row>
<row>
<entry><structfield>typanalyze</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Custom ANALYZE function, or 0 to use the standard function</entry>
</row>
<row>
<entry><structfield>typalign</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry><para>
<structfield>typalign</structfield> is the alignment required
when storing a value of this type. It applies to storage on
disk as well as most representations of the value inside
<productname>PostgreSQL</>.
When multiple values are stored consecutively, such
as in the representation of a complete row on disk, padding is
inserted before a datum of this type so that it begins on the
specified boundary. The alignment reference is the beginning
of the first datum in the sequence.
</para><para>
Possible values are:
<itemizedlist>
<listitem>
<para><literal>c</> = <type>char</type> alignment, i.e., no alignment needed.</para>
</listitem>
<listitem>
<para><literal>s</> = <type>short</type> alignment (2 bytes on most machines).</para>
</listitem>
<listitem>
<para><literal>i</> = <type>int</type> alignment (4 bytes on most machines).</para>
</listitem>
<listitem>
<para><literal>d</> = <type>double</type> alignment (8 bytes on many machines, but by no means all).</para>
</listitem>
</itemizedlist>
</para><note>
<para>
For types used in system tables, it is critical that the size
and alignment defined in <structname>pg_type</structname>
agree with the way that the compiler will lay out the column in
a structure representing a table row.
</para>
</note></entry>
</row>
<row>
<entry><structfield>typstorage</structfield></entry>
<entry><type>char</type></entry>
<entry></entry>
<entry><para>
<structfield>typstorage</structfield> tells for varlena
types (those with <structfield>typlen</structfield> = -1) if
the type is prepared for toasting and what the default strategy
for attributes of this type should be.
Possible values are
<itemizedlist>
<listitem>
<para><literal>p</>: Value must always be stored plain.</para>
</listitem>
<listitem>
<para>
<literal>e</>: Value can be stored in a <quote>secondary</quote>
relation (if relation has one, see
<literal>pg_class.reltoastrelid</literal>).
</para>
</listitem>
<listitem>
<para><literal>m</>: Value can be stored compressed inline.</para>
</listitem>
<listitem>
<para><literal>x</>: Value can be stored compressed inline or stored in <quote>secondary</quote> storage.</para>
</listitem>
</itemizedlist>
Note that <literal>m</> columns can also be moved out to secondary
storage, but only as a last resort (<literal>e</> and <literal>x</> columns are
moved first).
</para></entry>
</row>
<row>
<entry><structfield>typnotnull</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry><para>
<structfield>typnotnull</structfield> represents a not-null
constraint on a type. Used for domains only.
</para></entry>
</row>
<row>
<entry><structfield>typbasetype</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry><para>
If this is a domain (see <structfield>typtype</structfield>),
then <structfield>typbasetype</structfield> identifies
the type that this one is based on. Zero if not a domain.
</para></entry>
</row>
<row>
<entry><structfield>typtypmod</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry><para>
Domains use <structfield>typtypmod</structfield> to record the <literal>typmod</>
to be applied to their base type (-1 if base type does not use a
<literal>typmod</>). -1 if this type is not a domain.
</para></entry>
</row>
<row>
<entry><structfield>typndims</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry><para>
<structfield>typndims</structfield> is the number of array dimensions
for a domain that is an array (that is, <structfield>typbasetype</> is an array type;
the domain's <structfield>typelem</> will match the base type's <structfield>typelem</structfield>).
Zero for types other than array domains.
</para></entry>
</row>
<row>
<entry><structfield>typdefaultbin</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry><para>
If <structfield>typdefaultbin</> is not null, it is the <function>nodeToString()</function>
representation of a default expression for the type. This is
only used for domains.
</para></entry>
</row>
<row>
<entry><structfield>typdefault</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry><para>
<structfield>typdefault</> is null if the type has no associated
default value. If <structfield>typdefaultbin</> is not null,
<structfield>typdefault</> must contain a human-readable version of the
default expression represented by <structfield>typdefaultbin</>. If
<structfield>typdefaultbin</> is null and <structfield>typdefault</> is
not, then <structfield>typdefault</> is the external representation of
the type's default value, which may be fed to the type's input
converter to produce a constant.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="views-overview">
<title>System Views</title>
<para>
In addition to the system catalogs, <productname>PostgreSQL</productname>
provides a number of built-in views. Some system views provide convenient
access to some commonly used queries on the system catalogs. Other views
provide access to internal server state.
</para>
<para>
The information schema (<xref linkend="information-schema">) provides
an alternative set of views which overlap the functionality of the system
views. Since the information schema is SQL-standard whereas the views
described here are <productname>PostgreSQL</productname>-specific,
it's usually better to use the information schema if it provides all
the information you need.
</para>
<para>
<xref linkend="view-table"> lists the system views described here.
More detailed documentation of each view follows below.
There are some additional views that provide access to the results of
the statistics collector; they are described in <xref
linkend="monitoring-stats-views-table">.
</para>
<para>
Except where noted, all the views described here are read-only.
</para>
<table id="view-table">
<title>System Views</title>
<tgroup cols="2">
<thead>
<row>
<entry>View Name</entry>
<entry>Purpose</entry>
</row>
</thead>
<tbody>
<row>
<entry><link linkend="view-pg-cursors"><structname>pg_cursors</structname></link></entry>
<entry>open cursors</entry>
</row>
<row>
<entry><link linkend="view-pg-group"><structname>pg_group</structname></link></entry>
<entry>groups of database users</entry>
</row>
<row>
<entry><link linkend="view-pg-indexes"><structname>pg_indexes</structname></link></entry>
<entry>indexes</entry>
</row>
<row>
<entry><link linkend="view-pg-locks"><structname>pg_locks</structname></link></entry>
<entry>currently held locks</entry>
</row>
<row>
<entry><link linkend="view-pg-prepared-statements"><structname>pg_prepared_statements</structname></link></entry>
<entry>prepared statements</entry>
</row>
<row>
<entry><link linkend="view-pg-prepared-xacts"><structname>pg_prepared_xacts</structname></link></entry>
<entry>prepared transactions</entry>
</row>
<row>
<entry><link linkend="view-pg-roles"><structname>pg_roles</structname></link></entry>
<entry>database roles</entry>
</row>
<row>
<entry><link linkend="view-pg-rules"><structname>pg_rules</structname></link></entry>
<entry>rules</entry>
</row>
<row>
<entry><link linkend="view-pg-settings"><structname>pg_settings</structname></link></entry>
<entry>parameter settings</entry>
</row>
<row>
<entry><link linkend="view-pg-shadow"><structname>pg_shadow</structname></link></entry>
<entry>database users</entry>
</row>
<row>
<entry><link linkend="view-pg-stats"><structname>pg_stats</structname></link></entry>
<entry>planner statistics</entry>
</row>
<row>
<entry><link linkend="view-pg-tables"><structname>pg_tables</structname></link></entry>
<entry>tables</entry>
</row>
<row>
<entry><link linkend="view-pg-timezone-abbrevs"><structname>pg_timezone_abbrevs</structname></link></entry>
<entry>time zone abbreviations</entry>
</row>
<row>
<entry><link linkend="view-pg-timezone-names"><structname>pg_timezone_names</structname></link></entry>
<entry>time zone names</entry>
</row>
<row>
<entry><link linkend="view-pg-user"><structname>pg_user</structname></link></entry>
<entry>database users</entry>
</row>
<row>
<entry><link linkend="view-pg-views"><structname>pg_views</structname></link></entry>
<entry>views</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="view-pg-cursors">
<title><structname>pg_cursors</structname></title>
<indexterm zone="view-pg-cursors">
<primary>pg_cursors</primary>
</indexterm>
<para>
The <structname>pg_cursors</structname> view lists the cursors that
are currently available. Cursors can be defined in several ways:
<itemizedlist>
<listitem>
<para>
via the <xref linkend="sql-declare" endterm="sql-declare-title">
statement in SQL
</para>
</listitem>
<listitem>
<para>
via the Bind message in the frontend/backend protocol, as
described in <xref linkend="protocol-flow-ext-query">
</para>
</listitem>
<listitem>
<para>
via the Server Programming Interface (SPI), as described in
<xref linkend="spi-interface">
</para>
</listitem>
</itemizedlist>
The <structname>pg_cursors</structname> view displays cursors
created by any of these means. Cursors only exist for the duration
of the transaction that defines them, unless they have been
declared <literal>WITH HOLD</literal>. Therefore non-holdable
cursors are only present in the view until the end of their
creating transaction.
<note>
<para>
Cursors are used internally to implement some of the components
of <productname>PostgreSQL</>, such as procedural languages.
Therefore, the <structname>pg_cursors</> view may include cursors
that have not been explicitly created by the user.
</para>
</note>
</para>
<table>
<title><structname>pg_cursors</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>name</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>The name of the cursor</entry>
</row>
<row>
<entry><structfield>statement</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>The verbatim query string submitted to declare this cursor</entry>
</row>
<row>
<entry><structfield>is_holdable</structfield></entry>
<entry><type>boolean</type></entry>
<entry></entry>
<entry>
<literal>true</literal> if the cursor is holdable (that is, it
can be accessed after the transaction that declared the cursor
has committed); <literal>false</literal> otherwise
</entry>
</row>
<row>
<entry><structfield>is_binary</structfield></entry>
<entry><type>boolean</type></entry>
<entry></entry>
<entry>
<literal>true</literal> if the cursor was declared
<literal>BINARY</literal>; <literal>false</literal>
otherwise
</entry>
</row>
<row>
<entry><structfield>is_scrollable</structfield></entry>
<entry><type>boolean</type></entry>
<entry></entry>
<entry>
<literal>true</> if the cursor is scrollable (that is, it
allows rows to be retrieved in a nonsequential manner);
<literal>false</literal> otherwise
</entry>
</row>
<row>
<entry><structfield>creation_time</structfield></entry>
<entry><type>timestamptz</type></entry>
<entry></entry>
<entry>The time at which the cursor was declared</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <structname>pg_cursors</structname> view is read only.
</para>
</sect1>
<sect1 id="view-pg-group">
<title><structname>pg_group</structname></title>
<indexterm zone="view-pg-group">
<primary>pg_group</primary>
</indexterm>
<para>
The view <structname>pg_group</structname> exists for backwards
compatibility: it emulates a catalog that existed in
<productname>PostgreSQL</productname> before version 8.1.
It shows the names and members of all roles that are marked as not
<structfield>rolcanlogin</>, which is an approximation to the set
of roles that are being used as groups.
</para>
<table>
<title><structname>pg_group</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>groname</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
<entry>Name of the group</entry>
</row>
<row>
<entry><structfield>grosysid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>ID of this group</entry>
</row>
<row>
<entry><structfield>grolist</structfield></entry>
<entry><type>oid[]</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>An array containing the IDs of the roles in this group</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="view-pg-indexes">
<title><structname>pg_indexes</structname></title>
<indexterm zone="view-pg-indexes">
<primary>pg_indexes</primary>
</indexterm>
<para>
The view <structname>pg_indexes</structname> provides access to
useful information about each index in the database.
</para>
<table>
<title><structname>pg_indexes</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>schemaname</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
<entry>name of schema containing table and index</entry>
</row>
<row>
<entry><structfield>tablename</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
<entry>name of table the index is for</entry>
</row>
<row>
<entry><structfield>indexname</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
<entry>name of index</entry>
</row>
<row>
<entry><structfield>tablespace</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.spcname</literal></entry>
<entry>name of tablespace containing index (NULL if default for database)</entry>
</row>
<row>
<entry><structfield>indexdef</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>index definition (a reconstructed creation command)</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="view-pg-locks">
<title><structname>pg_locks</structname></title>
<indexterm zone="view-pg-locks">
<primary>pg_locks</primary>
</indexterm>
<para>
The view <structname>pg_locks</structname> provides access to
information about the locks held by open transactions within the
database server. See <xref linkend="mvcc"> for more discussion
of locking.
</para>
<para>
<structname>pg_locks</structname> contains one row per active lockable
object, requested lock mode, and relevant transaction. Thus, the same
lockable object may
appear many times, if multiple transactions are holding or waiting
for locks on it. However, an object that currently has no locks on it
will not appear at all.
</para>
<para>
There are several distinct types of lockable objects:
whole relations (e.g., tables), individual pages of relations,
individual tuples of relations,
transaction IDs,
and general database objects (identified by class OID and object OID,
in the same way as in <structname>pg_description</structname> or
<structname>pg_depend</structname>). Also, the right to extend a
relation is represented as a separate lockable object.
</para>
<table>
<title><structname>pg_locks</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>locktype</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>
type of the lockable object:
<literal>relation</>,
<literal>extend</>,
<literal>page</>,
<literal>tuple</>,
<literal>transactionid</>,
<literal>object</>,
<literal>userlock</>, or
<literal>advisory</>
</entry>
</row>
<row>
<entry><structfield>database</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.oid</literal></entry>
<entry>
OID of the database in which the object exists, or
zero if the object is a shared object, or
NULL if the object is a transaction ID
</entry>
</row>
<row>
<entry><structfield>relation</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>
OID of the relation, or NULL if the object is not
a relation or part of a relation
</entry>
</row>
<row>
<entry><structfield>page</structfield></entry>
<entry><type>integer</type></entry>
<entry></entry>
<entry>
page number within the relation, or NULL if the object
is not a tuple or relation page
</entry>
</row>
<row>
<entry><structfield>tuple</structfield></entry>
<entry><type>smallint</type></entry>
<entry></entry>
<entry>
tuple number within the page, or NULL if the object is not a tuple
</entry>
</row>
<row>
<entry><structfield>transactionid</structfield></entry>
<entry><type>xid</type></entry>
<entry></entry>
<entry>
ID of a transaction, or NULL if the object is not a transaction ID
</entry>
</row>
<row>
<entry><structfield>classid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>
OID of the system catalog containing the object, or NULL if the
object is not a general database object
</entry>
</row>
<row>
<entry><structfield>objid</structfield></entry>
<entry><type>oid</type></entry>
<entry>any OID column</entry>
<entry>
OID of the object within its system catalog, or NULL if the
object is not a general database object
</entry>
</row>
<row>
<entry><structfield>objsubid</structfield></entry>
<entry><type>smallint</type></entry>
<entry></entry>
<entry>
For a table column, this is the column number (the
<structfield>classid</> and <structfield>objid</> refer to the
table itself). For all other object types, this column is
zero. NULL if the object is not a general database object
</entry>
</row>
<row>
<entry><structfield>transaction</structfield></entry>
<entry><type>xid</type></entry>
<entry></entry>
<entry>
ID of the transaction that is holding or awaiting this lock
</entry>
</row>
<row>
<entry><structfield>pid</structfield></entry>
<entry><type>integer</type></entry>
<entry></entry>
<entry>
Process ID of the server process holding or awaiting this
lock. NULL if the lock is held by a prepared transaction.
</entry>
</row>
<row>
<entry><structfield>mode</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>name of the lock mode held or desired by this process (see <xref
linkend="locking-tables">)</entry>
</row>
<row>
<entry><structfield>granted</structfield></entry>
<entry><type>boolean</type></entry>
<entry></entry>
<entry>true if lock is held, false if lock is awaited</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<structfield>granted</structfield> is true in a row representing a lock
held by the indicated transaction. False indicates that this transaction is
currently waiting to acquire this lock, which implies that some other
transaction is holding a conflicting lock mode on the same lockable object.
The waiting transaction will sleep until the other lock is released (or a
deadlock situation is detected). A single transaction can be waiting to
acquire at most one lock at a time.
</para>
<para>
Every transaction holds an exclusive lock on its transaction ID for its
entire duration. If one transaction finds it necessary to wait specifically
for another transaction, it does so by attempting to acquire share lock on
the other transaction ID. That will succeed only when the other transaction
terminates and releases its locks.
</para>
<para>
Although tuples are a lockable type of object,
information about row-level locks is stored on disk, not in memory,
and therefore row-level locks normally do not appear in this view.
If a transaction is waiting for a
row-level lock, it will usually appear in the view as waiting for the
transaction ID of the current holder of that row lock.
</para>
<para>
Advisory locks can be acquired on keys consisting of either a single
bigint value or two integer values. A bigint key is displayed with its
high-order half in the <structfield>classid</> column, its low-order half
in the <structfield>objid</> column, and <structfield>objsubid</> equal
to 1. Integer keys are displayed with the first key in the
<structfield>classid</> column, the second key in the <structfield>objid</>
column, and <structfield>objsubid</> equal to 2. The actual meaning of
the keys is up to the user. Advisory locks are local to each database,
so the <structfield>database</> column is meaningful for an advisory lock.
</para>
<para>
When the <structname>pg_locks</structname> view is accessed, the
internal lock manager data structures are momentarily locked, and
a copy is made for the view to display. This ensures that the
view produces a consistent set of results, while not blocking
normal lock manager operations longer than necessary. Nonetheless
there could be some impact on database performance if this view is
read often.
</para>
<para>
<structname>pg_locks</structname> provides a global view of all locks
in the database cluster, not only those relevant to the current database.
Although its <structfield>relation</structfield> column can be joined
against <structname>pg_class</>.<structfield>oid</> to identify locked
relations, this will only work correctly for relations in the current
database (those for which the <structfield>database</structfield> column
is either the current database's OID or zero).
</para>
<para>
If you have enabled the statistics collector, the
<structfield>pid</structfield> column can be joined to the
<structfield>procpid</structfield> column of the
<structname>pg_stat_activity</structname> view to get more
information on the session holding or waiting to hold the lock.
Also, if you are using prepared transactions, the
<structfield>transaction</> column can be joined to the
<structfield>transaction</structfield> column of the
<structname>pg_prepared_xacts</structname> view to get more
information on prepared transactions that hold locks.
(A prepared transaction can never be waiting for a lock,
but it continues to hold the locks it acquired while running.)
</para>
</sect1>
<sect1 id="view-pg-prepared-statements">
<title><structname>pg_prepared_statements</structname></title>
<indexterm zone="view-pg-prepared-statements">
<primary>pg_prepared_statements</primary>
</indexterm>
<para>
The <structname>pg_prepared_statements</structname> view displays
all the prepared statements that are available in the current
session. See <xref linkend="sql-prepare"
endterm="sql-prepare-title"> for more information about prepared
statements.
</para>
<para>
<structname>pg_prepared_statements</structname> contains one row
for each prepared statement. Rows are added to the view when a new
prepared statement is created and removed when a prepared statement
is released (for example, via the <xref linkend="sql-deallocate"
endterm="sql-deallocate-title"> command).
</para>
<table>
<title><structname>pg_prepared_statements</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>name</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>
The identifier of the prepared statement
</entry>
</row>
<row>
<entry><structfield>statement</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>
The query string submitted by the client to create this
prepared statement. For prepared statements created via SQL,
this is the <command>PREPARE</command> statement submitted by
the client. For prepared statements created via the
frontend/backend protocol, this is the text of the prepared
statement itself.
</entry>
</row>
<row>
<entry><structfield>prepare_time</structfield></entry>
<entry><type>timestamptz</type></entry>
<entry></entry>
<entry>
The time at which the prepared statement was created
</entry>
</row>
<row>
<entry><structfield>parameter_types</structfield></entry>
<entry><type>regtype[]</type></entry>
<entry></entry>
<entry>
The expected parameter types for the prepared statement in the
form of an array of <type>regtype</type>. The OID corresponding
to an element of this array can be obtained by casting the
<type>regtype</type> value to <type>oid</type>.
</entry>
</row>
<row>
<entry><structfield>from_sql</structfield></entry>
<entry><type>boolean</type></entry>
<entry></entry>
<entry>
<literal>true</literal> if the prepared statement was created
via the <command>PREPARE</command> SQL statement;
<literal>false</literal> if the statement was prepared via the
frontend/backend protocol
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <structname>pg_prepared_statements</structname> view is read only.
</para>
</sect1>
<sect1 id="view-pg-prepared-xacts">
<title><structname>pg_prepared_xacts</structname></title>
<indexterm zone="view-pg-prepared-xacts">
<primary>pg_prepared_xacts</primary>
</indexterm>
<para>
The view <structname>pg_prepared_xacts</structname> displays
information about transactions that are currently prepared for two-phase
commit (see <xref linkend="sql-prepare-transaction"
endterm="sql-prepare-transaction-title"> for details).
</para>
<para>
<structname>pg_prepared_xacts</structname> contains one row per prepared
transaction. An entry is removed when the transaction is committed or
rolled back.
</para>
<table>
<title><structname>pg_prepared_xacts</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>transaction</structfield></entry>
<entry><type>xid</type></entry>
<entry></entry>
<entry>
Numeric transaction identifier of the prepared transaction
</entry>
</row>
<row>
<entry><structfield>gid</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>
Global transaction identifier that was assigned to the transaction
</entry>
</row>
<row>
<entry><structfield>prepared</structfield></entry>
<entry><type>timestamp with time zone</type></entry>
<entry></entry>
<entry>
Time at which the transaction was prepared for commit
</entry>
</row>
<row>
<entry><structfield>owner</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
<entry>
Name of the user that executed the transaction
</entry>
</row>
<row>
<entry><structfield>database</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.datname</literal></entry>
<entry>
Name of the database in which the transaction was executed
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
When the <structname>pg_prepared_xacts</structname> view is accessed, the
internal transaction manager data structures are momentarily locked, and
a copy is made for the view to display. This ensures that the
view produces a consistent set of results, while not blocking
normal operations longer than necessary. Nonetheless
there could be some impact on database performance if this view is
read often.
</para>
</sect1>
<sect1 id="view-pg-roles">
<title><structname>pg_roles</structname></title>
<indexterm zone="view-pg-roles">
<primary>pg_roles</primary>
</indexterm>
<para>
The view <structname>pg_roles</structname> provides access to
information about database roles. This is simply a publicly
readable view of
<link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>
that blanks out the password field.
</para>
<para>
This view explicitly exposes the OID column of the underlying table,
since that is needed to do joins to other catalogs.
</para>
<table>
<title><structname>pg_roles</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>rolname</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>Role name</entry>
</row>
<row>
<entry><structfield>rolsuper</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Role has superuser privileges</entry>
</row>
<row>
<entry><structfield>rolinherit</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Role automatically inherits privileges of roles it is a
member of</entry>
</row>
<row>
<entry><structfield>rolcreaterole</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Role may create more roles</entry>
</row>
<row>
<entry><structfield>rolcreatedb</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Role may create databases</entry>
</row>
<row>
<entry><structfield>rolcatupdate</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
Role may update system catalogs directly. (Even a superuser may not do
this unless this column is true.)
</entry>
</row>
<row>
<entry><structfield>rolcanlogin</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
Role may log in, that is, this role can be given as the initial
session authorization identifier.
</entry>
</row>
<row>
<entry><structfield>rolconnlimit</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>
For roles that can log in, this sets maximum number of concurrent
connections this role can make. -1 means no limit.
</entry>
</row>
<row>
<entry><structfield>rolpassword</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Not the password (always reads as <literal>********</>)</entry>
</row>
<row>
<entry><structfield>rolvaliduntil</structfield></entry>
<entry><type>timestamptz</type></entry>
<entry></entry>
<entry>Password expiry time (only used for password authentication);
NULL if no expiration</entry>
</row>
<row>
<entry><structfield>rolconfig</structfield></entry>
<entry><type>text[]</type></entry>
<entry></entry>
<entry>Session defaults for run-time configuration variables</entry>
</row>
<row>
<entry><structfield>oid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>ID of role</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="view-pg-rules">
<title><structname>pg_rules</structname></title>
<indexterm zone="view-pg-rules">
<primary>pg_rules</primary>
</indexterm>
<para>
The view <structname>pg_rules</structname> provides access to
useful information about query rewrite rules.
</para>
<table>
<title><structname>pg_rules</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>schemaname</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
<entry>name of schema containing table</entry>
</row>
<row>
<entry><structfield>tablename</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
<entry>name of table the rule is for</entry>
</row>
<row>
<entry><structfield>rulename</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link>.rulename</literal></entry>
<entry>name of rule</entry>
</row>
<row>
<entry><structfield>definition</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>rule definition (a reconstructed creation command)</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <structname>pg_rules</structname> view excludes the ON SELECT rules of
views; those can be seen in <structname>pg_views</structname>.
</para>
</sect1>
<sect1 id="view-pg-settings">
<title><structname>pg_settings</structname></title>
<indexterm zone="view-pg-settings">
<primary>pg_settings</primary>
</indexterm>
<para>
The view <structname>pg_settings</structname> provides access to
run-time parameters of the server. It is essentially an alternative
interface to the <command>SHOW</> and <command>SET</> commands.
It also provides access to some facts about each parameter that are
not directly available from <command>SHOW</>, such as minimum and
maximum values.
</para>
<table>
<title><structname>pg_settings</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>name</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>run-time configuration parameter name</entry>
</row>
<row>
<entry><structfield>setting</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>current value of the parameter</entry>
</row>
<row>
<entry><structfield>unit</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>implicit unit of the parameter</entry>
</row>
<row>
<entry><structfield>category</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>logical group of the parameter</entry>
</row>
<row>
<entry><structfield>short_desc</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>a brief description of the parameter</entry>
</row>
<row>
<entry><structfield>extra_desc</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>additional, more detailed, information about the parameter</entry>
</row>
<row>
<entry><structfield>context</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>context required to set the parameter's value</entry>
</row>
<row>
<entry><structfield>vartype</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>parameter type (<literal>bool</>, <literal>integer</>,
<literal>real</>, or <literal>string</>)
</entry>
</row>
<row>
<entry><structfield>source</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>source of the current parameter value</entry>
</row>
<row>
<entry><structfield>min_val</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>minimum allowed value of the parameter (NULL for nonnumeric
values)</entry>
</row>
<row>
<entry><structfield>max_val</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>maximum allowed value of the parameter (NULL for nonnumeric
values)</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <structname>pg_settings</structname> view cannot be inserted into or
deleted from, but it can be updated. An <command>UPDATE</command> applied
to a row of <structname>pg_settings</structname> is equivalent to executing
the <xref linkend="SQL-SET" endterm="SQL-SET-title"> command on that named
parameter. The change only affects the value used by the current
session. If an <command>UPDATE</command> is issued within a transaction
that is later aborted, the effects of the <command>UPDATE</command> command
disappear when the transaction is rolled back. Once the surrounding
transaction is committed, the effects will persist until the end of the
session, unless overridden by another <command>UPDATE</command> or
<command>SET</command>.
</para>
</sect1>
<sect1 id="view-pg-shadow">
<title><structname>pg_shadow</structname></title>
<indexterm zone="view-pg-shadow">
<primary>pg_shadow</primary>
</indexterm>
<para>
The view <structname>pg_shadow</structname> exists for backwards
compatibility: it emulates a catalog that existed in
<productname>PostgreSQL</productname> before version 8.1.
It shows properties of all roles that are marked as
<structfield>rolcanlogin</>.
</para>
<para>
The name stems from the fact that this table
should not be readable by the public since it contains passwords.
<link linkend="view-pg-user"><structname>pg_user</structname></link>
is a publicly readable view on
<structname>pg_shadow</structname> that blanks out the password field.
</para>
<table>
<title><structname>pg_shadow</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>usename</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
<entry>User name</entry>
</row>
<row>
<entry><structfield>usesysid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
<entry>ID of this user</entry>
</row>
<row>
<entry><structfield>usecreatedb</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>User may create databases</entry>
</row>
<row>
<entry><structfield>usesuper</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>User is a superuser</entry>
</row>
<row>
<entry><structfield>usecatupd</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
User may update system catalogs. (Even a superuser may not do
this unless this column is true.)
</entry>
</row>
<row>
<entry><structfield>passwd</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Password (possibly encrypted)</entry>
</row>
<row>
<entry><structfield>valuntil</structfield></entry>
<entry><type>abstime</type></entry>
<entry></entry>
<entry>Password expiry time (only used for password authentication)</entry>
</row>
<row>
<entry><structfield>useconfig</structfield></entry>
<entry><type>text[]</type></entry>
<entry></entry>
<entry>Session defaults for run-time configuration variables</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="view-pg-stats">
<title><structname>pg_stats</structname></title>
<indexterm zone="view-pg-stats">
<primary>pg_stats</primary>
</indexterm>
<para>
The view <structname>pg_stats</structname> provides access to
the information stored in the <link
linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link>
catalog. This view allows access only to rows of
<structname>pg_statistic</structname> that correspond to tables the
user has permission to read, and therefore it is safe to allow public
read access to this view.
</para>
<para>
<structname>pg_stats</structname> is also designed to present the
information in a more readable format than the underlying catalog
&mdash; at the cost that its schema must be extended whenever new slot types
are defined for <structname>pg_statistic</structname>.
</para>
<table>
<title><structname>pg_stats</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>schemaname</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
<entry>name of schema containing table</entry>
</row>
<row>
<entry><structfield>tablename</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
<entry>name of table</entry>
</row>
<row>
<entry><structfield>attname</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attname</literal></entry>
<entry>name of the column described by this row</entry>
</row>
<row>
<entry><structfield>null_frac</structfield></entry>
<entry><type>real</type></entry>
<entry></entry>
<entry>fraction of column entries that are null</entry>
</row>
<row>
<entry><structfield>avg_width</structfield></entry>
<entry><type>integer</type></entry>
<entry></entry>
<entry>average width in bytes of column's entries</entry>
</row>
<row>
<entry><structfield>n_distinct</structfield></entry>
<entry><type>real</type></entry>
<entry></entry>
<entry>If greater than zero, the estimated number of distinct values
in the column. If less than zero, the negative of the number of
distinct values divided by the number of rows. (The negated form
is used when <command>ANALYZE</> believes that the number of distinct
values
is likely to increase as the table grows; the positive form is used
when the column seems to have a fixed number of possible values.)
For example, -1 indicates a unique column in which the number of
distinct values is the same as the number of rows.
</entry>
</row>
<row>
<entry><structfield>most_common_vals</structfield></entry>
<entry><type>anyarray</type></entry>
<entry></entry>
<entry>A list of the most common values in the column. (NULL if
no values seem to be more common than any others.)</entry>
</row>
<row>
<entry><structfield>most_common_freqs</structfield></entry>
<entry><type>real[]</type></entry>
<entry></entry>
<entry>A list of the frequencies of the most common values,
i.e., number of occurrences of each divided by total number of rows.
(NULL when <structfield>most_common_vals</structfield> is.)
</entry>
</row>
<row>
<entry><structfield>histogram_bounds</structfield></entry>
<entry><type>anyarray</type></entry>
<entry></entry>
<entry>A list of values that divide the column's values into
groups of approximately equal population. The values in
<structfield>most_common_vals</>, if present, are omitted from this
histogram calculation. (This column is NULL if the column data type
does not have a <literal>&lt;</> operator or if the
<structfield>most_common_vals</> list accounts for the entire
population.)
</entry>
</row>
<row>
<entry><structfield>correlation</structfield></entry>
<entry><type>real</type></entry>
<entry></entry>
<entry>Statistical correlation between physical row ordering and
logical ordering of the column values. This ranges from -1 to +1.
When the value is near -1 or +1, an index scan on the column will
be estimated to be cheaper than when it is near zero, due to reduction
of random access to the disk. (This column is NULL if the column data
type does not have a <literal>&lt;</> operator.)
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The maximum number of entries in the <structfield>most_common_vals</>
and <structfield>histogram_bounds</> arrays can be set on a
column-by-column basis using the <command>ALTER TABLE SET STATISTICS</>
command, or globally by setting the
<xref linkend="guc-default-statistics-target"> run-time parameter.
</para>
</sect1>
<sect1 id="view-pg-tables">
<title><structname>pg_tables</structname></title>
<indexterm zone="view-pg-tables">
<primary>pg_tables</primary>
</indexterm>
<para>
The view <structname>pg_tables</structname> provides access to
useful information about each table in the database.
</para>
<table>
<title><structname>pg_tables</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>schemaname</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
<entry>name of schema containing table</entry>
</row>
<row>
<entry><structfield>tablename</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
<entry>name of table</entry>
</row>
<row>
<entry><structfield>tableowner</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
<entry>name of table's owner</entry>
</row>
<row>
<entry><structfield>tablespace</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.spcname</literal></entry>
<entry>name of tablespace containing table (NULL if default for database)</entry>
</row>
<row>
<entry><structfield>hasindexes</structfield></entry>
<entry><type>boolean</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relhasindex</literal></entry>
<entry>true if table has (or recently had) any indexes</entry>
</row>
<row>
<entry><structfield>hasrules</structfield></entry>
<entry><type>boolean</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relhasrules</literal></entry>
<entry>true if table has rules</entry>
</row>
<row>
<entry><structfield>hastriggers</structfield></entry>
<entry><type>boolean</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.reltriggers</literal></entry>
<entry>true if table has triggers</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="view-pg-timezone-abbrevs">
<title><structname>pg_timezone_abbrevs</structname></title>
<indexterm zone="view-pg-timezone-abbrevs">
<primary>pg_timezone_abbrevs</primary>
</indexterm>
<para>
The view <structname>pg_timezone_abbrevs</structname> provides a list
of time zone abbreviations that are currently recognized by the datetime
input routines. The contents of this view change when the
<xref linkend="guc-timezone-abbreviations"> run-time parameter is modified.
</para>
<table>
<title><structname>pg_timezone_abbrevs</> Columns</title>
<tgroup cols=3>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>abbrev</structfield></entry>
<entry><type>text</type></entry>
<entry>time zone abbreviation</entry>
</row>
<row>
<entry><structfield>utc_offset</structfield></entry>
<entry><type>interval</type></entry>
<entry>offset from UTC (positive means east of Greenwich)</entry>
</row>
<row>
<entry><structfield>is_dst</structfield></entry>
<entry><type>boolean</type></entry>
<entry>true if this is a daylight-savings abbreviation</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="view-pg-timezone-names">
<title><structname>pg_timezone_names</structname></title>
<indexterm zone="view-pg-timezone-names">
<primary>pg_timezone_names</primary>
</indexterm>
<para>
The view <structname>pg_timezone_names</structname> provides a list
of time zone names that are recognized by <command>SET TIMEZONE</>,
along with their associated abbreviations, UTC offsets,
and daylight-savings status.
Unlike the abbreviations shown in <link
linkend="view-pg-timezone-abbrevs"><structname>pg_timezone_abbrevs</structname></link>, many of these names imply a set of daylight-savings transition
date rules. Therefore, the associated information changes across local DST
boundaries. The displayed information is computed based on the current
value of <function>CURRENT_TIMESTAMP</>.
</para>
<table>
<title><structname>pg_timezone_names</> Columns</title>
<tgroup cols=3>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>name</structfield></entry>
<entry><type>text</type></entry>
<entry>time zone name</entry>
</row>
<row>
<entry><structfield>abbrev</structfield></entry>
<entry><type>text</type></entry>
<entry>time zone abbreviation</entry>
</row>
<row>
<entry><structfield>utc_offset</structfield></entry>
<entry><type>interval</type></entry>
<entry>offset from UTC (positive means east of Greenwich)</entry>
</row>
<row>
<entry><structfield>is_dst</structfield></entry>
<entry><type>boolean</type></entry>
<entry>true if currently observing daylight savings</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="view-pg-user">
<title><structname>pg_user</structname></title>
<indexterm zone="view-pg-user">
<primary>pg_user</primary>
</indexterm>
<para>
The view <structname>pg_user</structname> provides access to
information about database users. This is simply a publicly
readable view of
<link linkend="view-pg-shadow"><structname>pg_shadow</structname></link>
that blanks out the password field.
</para>
<table>
<title><structname>pg_user</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>usename</structfield></entry>
<entry><type>name</type></entry>
<entry></entry>
<entry>User name</entry>
</row>
<row>
<entry><structfield>usesysid</structfield></entry>
<entry><type>int4</type></entry>
<entry></entry>
<entry>User ID (arbitrary number used to reference this user)</entry>
</row>
<row>
<entry><structfield>usecreatedb</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>User may create databases</entry>
</row>
<row>
<entry><structfield>usesuper</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>User is a superuser</entry>
</row>
<row>
<entry><structfield>usecatupd</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>
User may update system catalogs. (Even a superuser may not do
this unless this column is true.)
</entry>
</row>
<row>
<entry><structfield>passwd</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>Not the password (always reads as <literal>********</>)</entry>
</row>
<row>
<entry><structfield>valuntil</structfield></entry>
<entry><type>abstime</type></entry>
<entry></entry>
<entry>Password expiry time (only used for password authentication)</entry>
</row>
<row>
<entry><structfield>useconfig</structfield></entry>
<entry><type>text[]</type></entry>
<entry></entry>
<entry>Session defaults for run-time configuration variables</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="view-pg-views">
<title><structname>pg_views</structname></title>
<indexterm zone="view-pg-views">
<primary>pg_views</primary>
</indexterm>
<para>
The view <structname>pg_views</structname> provides access to
useful information about each view in the database.
</para>
<table>
<title><structname>pg_views</> Columns</title>
<tgroup cols=4>
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>schemaname</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
<entry>name of schema containing view</entry>
</row>
<row>
<entry><structfield>viewname</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
<entry>name of view</entry>
</row>
<row>
<entry><structfield>viewowner</structfield></entry>
<entry><type>name</type></entry>
<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
<entry>name of view's owner</entry>
</row>
<row>
<entry><structfield>definition</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>view definition (a reconstructed <command>SELECT</command> query)</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
</chapter>
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