System Catalogs
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.
PostgreSQL'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, CREATE
DATABASE inserts a row into the
pg_database catalog — and actually
creates the database on disk.) There are some exceptions for
particularly esoteric operations, such as adding index access methods.
Overview lists the system catalogs.
More detailed documentation of each catalog follows below.
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.
System CatalogsCatalog NamePurposepg_aggregateaggregate functionspg_amindex access methodspg_amopaccess method operatorspg_amprocaccess method support procedurespg_attrdefcolumn default valuespg_attributetable columns (attributes)pg_castcasts (data type conversions)pg_classtables, indexes, sequences, views (relations)pg_constraintcheck constraints, unique constraints, primary key constraints, foreign key constraintspg_conversionencoding conversion informationpg_databasedatabases within this database clusterpg_dependdependencies between database objectspg_descriptiondescriptions or comments on database objectspg_groupgroups of database userspg_indexadditional index informationpg_inheritstable inheritance hierarchypg_languagelanguages for writing functionspg_largeobjectlarge objectspg_listenerasynchronous notification supportpg_namespaceschemaspg_opclassindex access method operator classespg_operatoroperatorspg_procfunctions and procedurespg_rewritequery rewrite rulespg_shadowdatabase userspg_statisticplanner statisticspg_tablespacetablespaces within this database clusterpg_triggertriggerspg_typedata types
pg_aggregatepg_aggregate
The catalog pg_aggregate 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
sum, count, and
max. Each entry in
pg_aggregate is an extension of an entry
in pg_proc. The pg_proc
entry carries the aggregate's name, input and output data types, and
other information that is similar to ordinary functions.
pg_aggregate> ColumnsNameTypeReferencesDescriptionaggfnoidregprocpg_proc.oidpg_proc OID of the aggregate functionaggtransfnregprocpg_proc.oidTransition functionaggfinalfnregprocpg_proc.oidFinal function (zero if none)aggtranstypeoidpg_type.oidThe type of the aggregate function's internal transition (state) dataagginitvaltext
The initial value of the transition state. This is a text
field containing the initial value in its external string
representation. If the value is null, the transition state
value starts out null.
New aggregate functions are registered with the CREATE
AGGREGATE command. See for more
information about writing aggregate functions and the meaning of
the transition functions, etc.
pg_ampg_am
The catalog pg_am 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
.
pg_am> ColumnsNameTypeReferencesDescriptionamnamenameName of the access methodamstrategiesint2Number of operator strategies for this access methodamsupportint2Number of support routines for this access methodamorderstrategyint2Zero if the index offers no sort order, otherwise the strategy
number of the strategy operator that describes the sort orderamcanuniqueboolDoes the access method support unique indexes?amcanmulticolboolDoes the access method support multicolumn indexes?amindexnullsboolDoes the access method support null index entries?amconcurrentboolDoes the access method support concurrent updates?aminsertregprocpg_proc.oidInsert this tuple functionambeginscanregprocpg_proc.oidStart new scan functionamgettupleregprocpg_proc.oidNext valid tuple functionamgetmultiregprocpg_proc.oidFetch multiple tuples functionamrescanregprocpg_proc.oidRestart this scan functionamendscanregprocpg_proc.oidEnd this scan functionammarkposregprocpg_proc.oidMark current scan position functionamrestrposregprocpg_proc.oidRestore marked scan position functionambuildregprocpg_proc.oidBuild new index functionambulkdeleteregprocpg_proc.oidBulk-delete functionamvacuumcleanupregprocpg_proc.oidPost-VACUUM cleanup functionamcostestimateregprocpg_proc.oidFunction to estimate cost of an index scan
pg_amoppg_amop
The catalog pg_amop 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.
pg_amop> ColumnsNameTypeReferencesDescriptionamopclaidoidpg_opclass.oidThe index operator class this entry is foramopsubtypeoidpg_type.oidSubtype to distinguish multiple entries for one strategy;
zero for defaultamopstrategyint2Operator strategy numberamopreqcheckboolIndex hit must be recheckedamopoproidpg_operator.oidOID of the operator
pg_amprocpg_amproc
The catalog pg_amproc 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.
pg_amproc ColumnsNameTypeReferencesDescriptionamopclaidoidpg_opclass.oidThe index operator class this entry is foramprocsubtypeoidpg_type.oidSubtype, if cross-type routine, else zeroamprocnumint2Support procedure numberamprocregprocpg_proc.oidOID of the procedure
pg_attrdefpg_attrdef
The catalog pg_attrdef stores column default values. The main information
about columns is stored in pg_attribute
(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.
pg_attrdef> ColumnsNameTypeReferencesDescriptionadrelidoidpg_class.oidThe table this column belongs toadnumint2pg_attribute.attnumThe number of the columnadbintextThe internal representation of the column default valueadsrctextA human-readable representation of the default value
The adsrc 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
adbin field (with pg_get_expr> for
example) is a better way to display the default value.
pg_attributepg_attribute
The catalog pg_attribute stores information about
table columns. There will be exactly one
pg_attribute row for every column in every
table in the database. (There will also be attribute entries for
indexes, and indeed all objects that have pg_class
entries.)
The term attribute is equivalent to column and is used for
historical reasons.
pg_attribute> ColumnsNameTypeReferencesDescriptionattrelidoidpg_class.oidThe table this column belongs toattnamenameThe column nameatttypidoidpg_type.oidThe data type of this columnattstattargetint4attstattarget controls the level of detail
of statistics accumulated for this column by
.
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, attstattarget
is both the target number of most common values
to collect, and the target number of histogram bins to create.
attlenint2
A copy of pg_type.typlen of this column's
type
attnumint2
The number of the column. Ordinary columns are numbered from 1
up. System columns, such as oid,
have (arbitrary) negative numbers.
attndimsint4
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 it's an array>.)
attcacheoffint4
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.
atttypmodint4atttypmod records type-specific data
supplied at table creation time (for example, the maximum
length of a varchar 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 atttypmod>.
attbyvalbool
A copy of pg_type.typbyval> of this column's type
attstoragechar
Normally a copy of pg_type.typstorage> of this
column's type. For TOAST-able data types, this can be altered
after column creation to control storage policy.
attalignchar
A copy of pg_type.typalign> of this column's type
attnotnullbool
This represents a not-null constraint. It is possible to
change this column to enable or disable the constraint.
atthasdefbool
This column has a default value, in which case there will be a
corresponding entry in the pg_attrdef
catalog that actually defines the value.
attisdroppedbool
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.
attislocalbool
This column is defined locally in the relation. Note that a column may
be locally defined and inherited simultaneously.
attinhcountint4
The number of direct ancestors this column has. A column with a
nonzero number of ancestors cannot be dropped nor renamed.
In a dropped column's pg_attribute entry,
atttypid is reset to zero, but
attlen and the other fields copied from
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 pg_type> row anymore.
attlen and the other fields can be used
to interpret the contents of a row of the table.
pg_castpg_cast
The catalog pg_cast stores data type conversion paths,
both built-in paths and those defined with CREATE CAST.
pg_cast> ColumnsNameTypeReferencesDescriptioncastsourceoidpg_type.oidOID of the source data typecasttargetoidpg_type.oidOID of the target data typecastfuncoidpg_proc.oid
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).
castcontextchar
Indicates what contexts the cast may be invoked in.
e> means only as an explicit cast (using
CAST> or ::> syntax).
a> means implicitly in assignment
to a target column, as well as explicitly.
i> means implicitly in expressions, as well as the
other cases.
The cast functions listed in pg_cast 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 integer>; it receives the type
modifier associated with the destination type, or -1>
if there is none. The third argument,
if present, must be type boolean>; it receives true>
if the cast is an explicit cast, false> otherwise.
It is legitimate to create a pg_cast entry
in which the source and target types are the same, if the associated
function takes more than one argument. Such entries represent
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.
When a pg_cast 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.
pg_classpg_class
The catalog pg_class catalogs tables and most
everything else that has columns or is otherwise similar to a
table. This includes indexes (but see also
pg_index), sequences, views, composite types,
and some kinds of special relation; see relkind>.
Below, when we mean all of these
kinds of objects we speak of relations. Not all
columns are meaningful for all relation types.
pg_class> ColumnsNameTypeReferencesDescriptionrelnamenameName of the table, index, view, etc.relnamespaceoidpg_namespace.oid
The OID of the namespace that contains this relation
reltypeoidpg_type.oid
The OID of the data type that corresponds to this table's row type,
if any (zero for indexes, which have no pg_type> entry)
relownerint4pg_shadow.usesysidOwner of the relationrelamoidpg_am.oidIf this is an index, the access method used (B-tree, hash, etc.)relfilenodeoidName of the on-disk file of this relation; 0 if nonereltablespaceoidpg_tablespace.oid
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.)
relpagesint4
Size of the on-disk representation of this table in pages (of size
BLCKSZ).
This is only an estimate used by the planner.
It is updated by VACUUM,
ANALYZE, and a few DDL commands
such as CREATE INDEX.
reltuplesfloat4
Number of rows in the table.
This is only an estimate used by the planner.
It is updated by VACUUM,
ANALYZE, and a few DDL commands
such as CREATE INDEX.
reltoastrelidoidpg_class.oid
OID of the TOAST table associated with this table, 0 if none.
The TOAST table stores large attributes out of
line in a secondary table.
reltoastidxidoidpg_class.oid
For a TOAST table, the OID of its index. 0 if not a TOAST table.
relhasindexbool
True if this is a table and it has (or recently had) any
indexes. This is set by CREATE INDEX, but
not cleared immediately by DROP INDEX.
VACUUM clears relhasindex> if it finds the
table has no indexes.
relissharedboolTrue if this table is shared across all databases in the
cluster. Only certain system catalogs (such as
pg_database) are shared.relkindcharr> = ordinary table, i> = index,
S> = sequence, v> = view, c> =
composite type, s> = special, t> = TOAST
table
relnattsint2
Number of user columns in the relation (system columns not
counted). There must be this many corresponding entries in
pg_attribute. See also
pg_attribute.attnum.
relchecksint2
Number of check constraints on the table; see
pg_constraint catalog
reltriggersint2
Number of triggers on the table; see
pg_trigger catalog
relukeysint2unused (not the number of unique keys)relfkeysint2unused (not the number of foreign keys on the table)relrefsint2unusedrelhasoidsbool
True if we generate an OID for each row of the relation.
relhaspkeybool
True if the table has (or once had) a primary key.
relhasrulesboolTrue if table has rules; see
pg_rewrite catalog.
relhassubclassboolTrue if table has (or once had) any inheritance children.relaclaclitem[]
Access privileges; see
and
for details.
pg_constraintpg_constraint
The catalog pg_constraint 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
pg_attribute> catalog.
Check constraints on domains are stored here, too.
pg_constraint> ColumnsNameTypeReferencesDescriptionconnamenameConstraint name (not necessarily unique!)connamespaceoidpg_namespace.oid
The OID of the namespace that contains this constraint
contypecharc> = check constraint,
f> = foreign key constraint,
p> = primary key constraint,
u> = unique constraint
condeferrableboolIs the constraint deferrable?condeferredboolIs the constraint deferred by default?conrelidoidpg_class.oidThe table this constraint is on; 0 if not a table constraintcontypidoidpg_type.oidThe domain this constraint is on; 0 if not a domain constraintconfrelidoidpg_class.oidIf a foreign key, the referenced table; else 0confupdtypecharForeign key update action codeconfdeltypecharForeign key deletion action codeconfmatchtypecharForeign key match typeconkeyint2[]pg_attribute.attnum>If a table constraint, list of columns which the constraint constrainsconfkeyint2[]pg_attribute.attnum>If a foreign key, list of the referenced columnsconbintextIf a check constraint, an internal representation of the expressionconsrctextIf a check constraint, a human-readable representation of the expression
consrc 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 pg_get_constraintdef()>
to extract the definition of a check constraint.
pg_class.relchecks needs to agree with the
number of check-constraint entries found in this table for the
given relation.
pg_conversionpg_conversion
The catalog pg_conversion describes the
available encoding conversion procedures. See
for more information.
pg_conversion> ColumnsNameTypeReferencesDescriptionconnamenameConversion name (unique within a namespace)connamespaceoidpg_namespace.oid
The OID of the namespace that contains this conversion
conownerint4pg_shadow.usesysidOwner of the conversionconforencodingint4Source encoding IDcontoencodingint4Destination encoding IDconprocregprocpg_proc.oidConversion procedurecondefaultboolTrue if this is the default conversion
pg_databasepg_database
The catalog pg_database stores information
about the available databases. Databases are created with the
CREATE DATABASE command. Consult
for details about the meaning of some of the
parameters.
Unlike most system catalogs, pg_database
is shared across all databases of a cluster: there is only one
copy of pg_database per cluster, not
one per database.
pg_database> ColumnsNameTypeReferencesDescriptiondatnamenameDatabase namedatdbaint4pg_shadow.usesysidOwner of the database, usually the user who created itencodingint4Character encoding for this databasedatistemplatebool
If true then this database can be used in the
TEMPLATE clause of CREATE
DATABASE to create a new database as a clone of
this one.
datallowconnbool
If false then no one can connect to this database. This is
used to protect the template0> database from being altered.
datlastsysoidoid
Last system OID in the database; useful
particularly to pg_dumpdatvacuumxidxid
All rows inserted or deleted by transaction IDs before this one
have been marked as known committed or known aborted in this database.
This is used to determine when commit-log space can be recycled.
datfrozenxidxid
All rows inserted by transaction IDs before this one have been
relabeled with a permanent (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.
dattablespaceoidpg_tablespace.oid
The default tablespace for the database.
Within this database, all tables for which
pg_class>.reltablespace> is zero
will be stored in this tablespace; in particular, all the non-shared
system catalogs will be there.
datconfigtext[]Session defaults for run-time configuration variablesdataclaclitem[]
Access privileges; see
and
for details.
pg_dependpg_depend
The catalog pg_depend records the dependency
relationships between database objects. This information allows
DROP> commands to find which other objects must be dropped
by DROP CASCADE> or prevent dropping in the DROP
RESTRICT> case.
pg_depend> ColumnsNameTypeReferencesDescriptionclassidoidpg_class.oidThe OID of the system catalog the dependent object is inobjidoidany OID columnThe OID of the specific dependent objectobjsubidint4
For a table column, this is the column number (the
objid> and classid> refer to the
table itself). For all other object types, this column is
zero.
refclassidoidpg_class.oidThe OID of the system catalog the referenced object is inrefobjidoidany OID columnThe OID of the specific referenced objectrefobjsubidint4
For a table column, this is the column number (the
refobjid> and refclassid> refer
to the table itself). For all other object types, this column
is zero.
deptypechar
A code defining the specific semantics of this dependency relationship; see text.
In all cases, a pg_depend entry indicates that the
referenced object may not be dropped without also dropping the dependent
object. However, there are several subflavors identified by
deptype>:
DEPENDENCY_NORMAL> (n>)
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 CASCADE>, in which case the dependent
object is dropped, too. Example: a table column has a normal
dependency on its data type.
DEPENDENCY_AUTO> (a>)
The dependent object can be dropped separately from the
referenced object, and should be automatically dropped
(regardless of RESTRICT> or 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.
DEPENDENCY_INTERNAL> (i>)
The dependent object was created as part of creation of the
referenced object, and is really just a part of its internal
implementation. A DROP> of the dependent object
will be disallowed outright (we'll tell the user to issue a
DROP> against the referenced object, instead). A
DROP> of the referenced object will be propagated
through to drop the dependent object whether
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
pg_constraint> entry.
DEPENDENCY_PIN> (p>)
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 initdb. The columns for the
dependent object contain zeroes.
Other dependency flavors may be needed in future.
pg_descriptionpg_description
The catalog pg_description> stores optional descriptions
(comments) for each database object. Descriptions can be manipulated
with the COMMENT command and viewed with
psql's \d commands.
Descriptions of many built-in system objects are provided in the initial
contents of pg_description.
pg_description> ColumnsNameTypeReferencesDescriptionobjoidoidany OID columnThe OID of the object this description pertains toclassoidoidpg_class.oidThe OID of the system catalog this object appears inobjsubidint4
For a comment on a table column, this is the column number (the
objoid> and classoid> refer to
the table itself). For all other object types, this column is
zero.
descriptiontextArbitrary text that serves as the description of this object.
pg_grouppg_group
The catalog pg_group defines groups and stores what users belong to what
groups. Groups are created with the CREATE
GROUP command. Consult for information
about user privilege management.
Because user and group identities are cluster-wide,
pg_group
is shared across all databases of a cluster: there is only one
copy of pg_group per cluster, not
one per database.
pg_group> ColumnsNameTypeReferencesDescriptiongronamenameName of the groupgrosysidint4An arbitrary number to identify this groupgrolistint4[]pg_shadow.usesysidAn array containing the IDs of the users in this group
pg_indexpg_index
The catalog pg_index contains part of the information
about indexes. The rest is mostly in
pg_class.
pg_index> ColumnsNameTypeReferencesDescriptionindexrelidoidpg_class.oidThe OID of the pg_class> entry for this indexindrelidoidpg_class.oidThe OID of the pg_class> entry for the table this index is forindkeyint2vectorpg_attribute.attnum
This is an array of indnatts (up to
INDEX_MAX_KEYS) values that indicate which
table columns this index indexes. For example a value of
1 3 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.
indclassoidvectorpg_opclass.oid
For each column in the index key this contains the OID of
the operator class to use. See
pg_opclass for details.
indnattsint2The number of columns in the index (duplicates
pg_class.relnatts)indisuniqueboolIf true, this is a unique index.indisprimaryboolIf true, this index represents the primary key of the table.
(indisunique> should always be true when this is true.)indisclusteredboolIf true, the table was last clustered on this index.indexprstextExpression trees (in nodeToString() representation)
for index attributes that are not simple column references. This is a
list with one element for each zero entry in indkey>.
Null if all index attributes are simple references.indpredtextExpression tree (in nodeToString() representation)
for partial index predicate. Null if not a partial index.
pg_inheritspg_inherits
The catalog 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.)
pg_inherits> ColumnsNameTypeReferencesDescriptioninhrelidoidpg_class.oid
The OID of the child table.
inhparentoidpg_class.oid
The OID of the parent table.
inhseqnoint4
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.
pg_languagepg_language
The catalog pg_language registers
languages in which you can write functions or stored procedures.
See
and for more information about language handlers.
pg_language> ColumnsNameTypeReferencesDescriptionlannamenameName of the languagelanisplbool
This is false for internal languages (such as
SQL) and true for user-defined languages.
Currently, pg_dump still uses this
to determine which languages need to be dumped, but this may be
replaced by a different mechanism sometime.
lanpltrustedbool
This is a trusted language. If this is an internal
language (lanispl is false) then
this column is meaningless.
lanplcallfoidoidpg_proc.oid
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.
lanvalidatoroidpg_proc.oid
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.
lanaclaclitem[]
Access privileges; see
and
for details.
pg_largeobjectpg_largeobject
The catalog pg_largeobject holds the data making up
large objects. A large object is identified by an
OID assigned when it is created. Each large object is broken into
segments or pages> small enough to be conveniently stored as rows
in pg_largeobject.
The amount of data per page is defined to be LOBLKSIZE> (which is currently
BLCKSZ/4>, or typically 2 kB).
pg_largeobject> ColumnsNameTypeReferencesDescriptionloidoidIdentifier of the large object that includes this pagepagenoint4Page number of this page within its large object
(counting from zero)databytea
Actual data stored in the large object.
This will never be more than LOBLKSIZE> bytes and may be less.
Each row of pg_largeobject holds data
for one page of a large object, beginning at
byte offset (pageno * LOBLKSIZE>) within the object. The implementation
allows sparse storage: pages may be missing, and may be shorter than
LOBLKSIZE> bytes even if they are not the last page of the object.
Missing regions within a large object read as zeroes.
pg_listenerpg_listener
The catalog pg_listener supports the
and
commands. A listener creates an entry in
pg_listener for each notification name
it is listening for. A notifier scans pg_listener
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.
pg_listener> ColumnsNameTypeReferencesDescriptionrelnamenameNotify condition name. (The name need not match any actual
relation in the database; the name relname> is historical.)
listenerpidint4PID of the server process that created this entry.notificationint4
Zero if no event is pending for this listener. If an event is
pending, the PID of the server process that sent the notification.
pg_namespacepg_namespace
The catalog 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.
pg_namespace> ColumnsNameTypeReferencesDescriptionnspnamenameName of the namespacenspownerint4pg_shadow.usesysidOwner of the namespacenspaclaclitem[]
Access privileges; see
and
for details.
pg_opclasspg_opclass
The catalog pg_opclass 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.
Operator classes are described at length in .
pg_opclass> ColumnsNameTypeReferencesDescriptionopcamidoidpg_am.oidIndex access method operator class is foropcnamenameName of this operator classopcnamespaceoidpg_namespace.oidNamespace of this operator classopcownerint4pg_shadow.usesysidOperator class owneropcintypeoidpg_type.oidData type that the operator class indexesopcdefaultboolTrue if this operator class is the default for opcintype>opckeytypeoidpg_type.oidType of data stored in index, or zero if same as opcintype>
The majority of the information defining an operator class is actually
not in its pg_opclass row, but in the associated
rows in pg_amop and
pg_amproc. Those rows are considered to be
part of the operator class definition — this is not unlike the way
that a relation is defined by a single pg_class
row plus associated rows in pg_attribute and
other tables.
pg_operatorpg_operator
The catalog pg_operator> stores information about operators.
See
and for more information.
pg_operator> ColumnsNameTypeReferencesDescriptionoprnamenameName of the operatoroprnamespaceoidpg_namespace.oid
The OID of the namespace that contains this operator
oprownerint4pg_shadow.usesysidOwner of the operatoroprkindcharb> = infix (both), l> = prefix
(left), r> = postfix (right)
oprcanhashboolThis operator supports hash joinsoprleftoidpg_type.oidType of the left operandoprrightoidpg_type.oidType of the right operandoprresultoidpg_type.oidType of the resultoprcomoidpg_operator.oidCommutator of this operator, if anyoprnegateoidpg_operator.oidNegator of this operator, if anyoprlsortopoidpg_operator.oid
If this operator supports merge joins, the operator that sorts
the type of the left-hand operand (L<L>)
oprrsortopoidpg_operator.oid
If this operator supports merge joins, the operator that sorts
the type of the right-hand operand (R<R>)
oprltcmpopoidpg_operator.oid
If this operator supports merge joins, the less-than operator that
compares the left and right operand types (L<R>)
oprgtcmpopoidpg_operator.oid
If this operator supports merge joins, the greater-than operator that
compares the left and right operand types (L>R>)
oprcoderegprocpg_proc.oidFunction that implements this operatoroprrestregprocpg_proc.oidRestriction selectivity estimation function for this operatoroprjoinregprocpg_proc.oidJoin selectivity estimation function for this operator
Unused column contain zeroes, for example oprleft is zero for a
prefix operator.
pg_procpg_proc
The catalog pg_proc> stores information about functions (or procedures).
See
and for more information.
The table contains data for aggregate functions as well as plain functions.
If proisagg is true, there should be a matching
row in pg_aggregate.
pg_proc> ColumnsNameTypeReferencesDescriptionpronamenameName of the functionpronamespaceoidpg_namespace.oid
The OID of the namespace that contains this function
proownerint4pg_shadow.usesysidOwner of the functionprolangoidpg_language.oidImplementation language or call interface of this functionproisaggboolFunction is an aggregate functionprosecdefboolFunction is a security definer (i.e., a setuid>
function)proisstrictbool
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 strict must be prepared to handle
null inputs.
proretsetboolFunction returns a set (i.e., multiple values of the specified
data type)provolatilecharprovolatile tells whether the function's
result depends only on its input arguments, or is affected by outside
factors.
It is i for immutable> functions,
which always deliver the same result for the same inputs.
It is s for stable> functions,
whose results (for fixed inputs) do not change within a scan.
It is v for volatile> functions,
whose results may change at any time. (Use v also
for functions with side-effects, so that calls to them cannot get
optimized away.)
pronargsint2Number of argumentsprorettypeoidpg_type.oidData type of the return valueproargtypesoidvectorpg_type.oidAn array with the data types of the function argumentsproargnamestext[]
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 may be null.
prosrctext
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.
probinbyteaAdditional information about how to invoke the function.
Again, the interpretation is language-specific.
proaclaclitem[]
Access privileges; see
and
for details.
For compiled functions, both built-in and dynamically loaded,
prosrc contains the function's C-language
name (link symbol). For all other currently-known language types,
prosrc contains the function's source
text. probin is unused except for
dynamically-loaded C functions, for which it gives the name of the
shared library file containing the function.
pg_rewritepg_rewrite
The catalog pg_rewrite stores rewrite rules for tables and views.
pg_rewrite> ColumnsNameTypeReferencesDescriptionrulenamenameRule nameev_classoidpg_class.oidThe table this rule is forev_attrint2The column this rule is for (currently, always zero to
indicate the whole table)ev_typechar
Event type that the rule is for: 1 = SELECT>, 2 =
UPDATE>, 3 = INSERT>, 4 =
DELETE>
is_insteadboolTrue if the rule is an INSTEAD ruleev_qualtext
Expression tree (in the form of a
nodeToString() representation) for the
rule's qualifying condition
ev_actiontext
Query tree (in the form of a
nodeToString() representation) for the
rule's action
pg_class.relhasrules
must be true if a table has any rules in this catalog.
pg_shadowpg_shadow
The catalog pg_shadow contains information about
database users. The name stems from the fact that this table
should not be readable by the public since it contains passwords.
pg_user
is a publicly readable view on
pg_shadow that blanks out the password field.
contains detailed information about user and
privilege management.
Because user identities are cluster-wide,
pg_shadow
is shared across all databases of a cluster: there is only one
copy of pg_shadow per cluster, not
one per database.
pg_shadow> ColumnsNameTypeReferencesDescriptionusenamenameUser nameusesysidint4User ID (arbitrary number used to reference this user)usecreatedbboolUser may create databasesusesuperboolUser is a superuserusecatupdbool
User may update system catalogs. (Even a superuser may not do
this unless this column is true.)
passwdtextPassword (possibly encrypted)valuntilabstimePassword expiry time (only used for password authentication)useconfigtext[]Session defaults for run-time configuration variables
pg_statisticpg_statistic
The catalog pg_statistic stores statistical data
about the contents of the database. Entries are created by
ANALYZE 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.
pg_statistic also stores statistical data about
the values of index expressions. These are described as if they were
actual data columns; in particular, starelid
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.
Since different kinds of statistics may be appropriate for different
kinds of data, pg_statistic 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 pg_statistic. Everything else
is stored in slots, 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
src/include/catalog/pg_statistic.h.
pg_statistic 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.)
pg_stats
is a publicly readable view on
pg_statistic that only exposes information
about those tables that are readable by the current user.
pg_statistic> ColumnsNameTypeReferencesDescriptionstarelidoidpg_class.oidThe table or index that the described column belongs tostaattnumint2pg_attribute.attnumThe number of the described columnstanullfracfloat4The fraction of the column's entries that are nullstawidthint4The average stored width, in bytes, of nonnull entriesstadistinctfloat4The 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 stadistinct> = -0.5).
A zero value means the number of distinct values is unknown.
stakindN>int2
A code number indicating the kind of statistics stored in the
N>th slot of the
pg_statistic row.
staopN>oidpg_operator.oid
An operator used to derive the statistics stored in the
N>th slot. For example, a
histogram slot would show the < operator
that defines the sort order of the data.
stanumbersN>float4[]
Numerical statistics of the appropriate kind for the
N>th slot, or null if the slot
kind does not involve numerical values.
stavaluesN>anyarray
Column data values of the appropriate kind for the
N>th slot, 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
anyarray>.
pg_tablespacepg_tablespace
The catalog pg_tablespace stores information
about the available tablespaces. Tables can be placed in particular
tablespaces to aid administration of disk layout.
Unlike most system catalogs, pg_tablespace
is shared across all databases of a cluster: there is only one
copy of pg_tablespace per cluster, not
one per database.
pg_tablespace> ColumnsNameTypeReferencesDescriptionspcnamenameTablespace namespcownerint4pg_shadow.usesysidOwner of the tablespace, usually the user who created itspclocationtextLocation (directory path) of the tablespacespcaclaclitem[]
Access privileges; see
and
for details.
pg_triggerpg_trigger
The catalog pg_trigger stores triggers on tables.
See
for more information.
pg_trigger> ColumnsNameTypeReferencesDescriptiontgrelidoidpg_class.oidThe table this trigger is ontgnamenameTrigger name (must be unique among triggers of same table)tgfoidoidpg_proc.oidThe function to be calledtgtypeint2Bit mask identifying trigger conditionstgenabledboolTrue if trigger is enabled (not presently checked everywhere
it should be, so disabling a trigger by setting this false does not
work reliably)tgisconstraintboolTrue if trigger implements a referential integrity constrainttgconstrnamenameReferential integrity constraint nametgconstrrelidoidpg_class.oidThe table referenced by an referential integrity constrainttgdeferrableboolTrue if deferrabletginitdeferredboolTrue if initially deferredtgnargsint2Number of argument strings passed to trigger functiontgattrint2vectorCurrently unusedtgargsbyteaArgument strings to pass to trigger, each null-terminated
pg_class.reltriggers needs to agree with the
number of triggers found in this table for the given relation.
pg_typepg_type
The catalog pg_type stores information about data
types. Base types (scalar types) are created with
, and
domains with
.
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 CREATE TYPE AS.
pg_type> ColumnsNameTypeReferencesDescriptiontypnamenameData type nametypnamespaceoidpg_namespace.oid
The OID of the namespace that contains this type
typownerint4pg_shadow.usesysidOwner of the typetyplenint2
For a fixed-size type, typlen is the number
of bytes in the internal representation of the type. But for a
variable-length type, typlen is negative.
-1 indicates a varlena> type (one that has a length word),
-2 indicates a null-terminated C string.
typbyvalbooltypbyval determines whether internal
routines pass a value of this type by value or by reference.
typbyval had better be false if
typlen 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
typbyval can be false even if the
length would allow pass-by-value; this is currently true for
type float4, for example.
typtypechartyptype is b for
a base type, c for a composite type (e.g., a
table's row type), d for a domain, or
p for a pseudo-type. See also
typrelid and
typbasetype.
typisdefinedbool
True if the type is defined, false if this is a placeholder
entry for a not-yet-defined type. When
typisdefined is false, nothing
except the type name, namespace, and OID can be relied on.
typdelimcharCharacter 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.typrelidoidpg_class.oid
If this is a composite type (see
typtype), then this column points to
the pg_class entry that defines the
corresponding table. (For a free-standing composite type, the
pg_class entry doesn't really represent
a table, but it is needed anyway for the type's
pg_attribute entries to link to.)
Zero for non-composite types.
typelemoidpg_type.oid
If typelem is not 0 then it
identifies another row in pg_type.
The current type can then be subscripted like an array yielding
values of type typelem. A
true array type is variable length
(typlen = -1),
but some fixed-length (typlen > 0) types
also have nonzero typelem, for example
name and oidvector.
If a fixed-length type has a typelem then
its internal representation must be some number of values of the
typelem data type with no other data.
Variable-length array types have a header defined by the array
subroutines.
typinputregprocpg_proc.oidInput conversion function (text format)typoutputregprocpg_proc.oidOutput conversion function (text format)typreceiveregprocpg_proc.oidInput conversion function (binary format), or 0 if nonetypsendregprocpg_proc.oidOutput conversion function (binary format), or 0 if nonetypanalyzeregprocpg_proc.oidCustom ANALYZE function, or 0 to use the standard functiontypalignchartypalign 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
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.
Possible values are:
c> = char alignment, i.e., no alignment needed.s> = short alignment (2 bytes on most machines).i> = int alignment (4 bytes on most machines).d> = double alignment (8 bytes on many machines, but by no means all).
For types used in system tables, it is critical that the size
and alignment defined in pg_type
agree with the way that the compiler will lay out the column in
a structure representing a table row.
typstoragechartypstorage tells for varlena
types (those with typlen = -1) if
the type is prepared for toasting and what the default strategy
for attributes of this type should be.
Possible values are
p>: Value must always be stored plain.e>: Value can be stored in a secondary
relation (if relation has one, see
pg_class.reltoastrelid).
m>: Value can be stored compressed inline.x>: Value can be stored compressed inline or stored in secondary storage.
Note that m> columns can also be moved out to secondary
storage, but only as a last resort (e> and x> columns are
moved first).
typnotnullbooltypnotnull represents a not-null
constraint on a type. Used for domains only.
typbasetypeoidpg_type.oid
If this is a domain (see typtype),
then typbasetype identifies
the type that this one is based on. Zero if not a domain.
typtypmodint4
Domains use typtypmod to record the typmod>
to be applied to their base type (-1 if base type does not use a
typmod>). -1 if this type is not a domain.
typndimsint4typndims is the number of array dimensions
for a domain that is an array (that is, typbasetype> is an array type;
the domain's typelem> will match the base type's typelem).
Zero for types other than array domains.
typdefaultbintext
If typdefaultbin> is not null, it is the nodeToString()
representation of a default expression for the type. This is
only used for domains.
typdefaulttexttypdefault> is null if the type has no associated
default value. If typdefaultbin> is not null,
typdefault> must contain a human-readable version of the
default expression represented by typdefaultbin>. If
typdefaultbin> is null and typdefault> is
not, then 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.
System Views
In addition to the system catalogs, PostgreSQL
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.
The 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 PostgreSQL-specific,
it's usually better to use the information schema if it provides all
the information you need.
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 .
Except where noted, all the views described here are read-only.
System ViewsView NamePurposepg_indexesindexespg_lockscurrently held lockspg_rulesrulespg_settingsparameter settingspg_statsplanner statisticspg_tablestablespg_userdatabase userspg_viewsviews
pg_indexespg_indexes
The view pg_indexes provides access to
useful information about each index in the database.
pg_indexes> ColumnsNameTypeReferencesDescriptionschemanamenamepg_namespace.nspnamename of schema containing table and indextablenamenamepg_class.relnamename of table the index is forindexnamenamepg_class.relnamename of indextablespacenamepg_tablespace.spcnamename of tablespace containing index (NULL if default for database)indexdeftextindex definition (a reconstructed creation command)
pg_lockspg_locks
The view pg_locks provides access to
information about the locks held by open transactions within the
database server. See for more discussion
of locking.
pg_locks 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. A lockable object is either a relation (e.g., a
table) or a transaction ID.
Note that this view includes only table-level
locks, not row-level ones. If a transaction is waiting for a
row-level lock, it will appear in the view as waiting for the
transaction ID of the current holder of that row lock.
pg_locks> ColumnsNameTypeReferencesDescriptionrelationoidpg_class.oid
OID of the locked relation, or NULL if the lockable object
is a transaction ID
databaseoidpg_database.oid
OID of the database in which the locked relation exists, or
zero if the locked relation is a globally-shared table, or
NULL if the lockable object is a transaction ID
transactionxid
ID of a transaction, or NULL if the lockable object is a relation
pidintegerprocess ID of a server process holding or awaiting this
lockmodetextname of the lock mode held or desired by this process (see )grantedbooleantrue if lock is held, false if lock is awaited
granted is true in a row representing a lock
held by the indicated session. False indicates that this session is
currently waiting to acquire this lock, which implies that some other
session is holding a conflicting lock mode on the same lockable object.
The waiting session will sleep until the other lock is released (or a
deadlock situation is detected). A single session can be waiting to acquire
at most one lock at a time.
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.
When the pg_locks 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.
pg_locks provides a global view of all locks
in the database cluster, not only those relevant to the current database.
Although its relation column can be joined
against pg_class>.oid> to identify locked
relations, this will only work correctly for relations in the current
database (those for which the database column
is either the current database's OID or zero).
If you have enabled the statistics collector, the
pid column can be joined to the
procpid column of the
pg_stat_activity view to get more
information on the session holding or waiting to hold the lock.
pg_rulespg_rules
The view pg_rules provides access to
useful information about query rewrite rules.
pg_rules> ColumnsNameTypeReferencesDescriptionschemanamenamepg_namespace.nspnamename of schema containing tabletablenamenamepg_class.relnamename of table the rule is forrulenamenamepg_rewrite.rulenamename of ruledefinitiontextrule definition (a reconstructed creation command)
The pg_rules view excludes the ON SELECT rules of
views; those can be seen in pg_views.
pg_settingspg_settings
The view pg_settings provides access to
run-time parameters of the server. It is essentially an alternative
interface to the SHOW> and SET> commands.
It also provides access to some facts about each parameter that are
not directly available from SHOW>, such as minimum and
maximum values.
pg_settings> ColumnsNameTypeReferencesDescriptionnametextrun-time configuration parameter namesettingtextcurrent value of the parametercategorytextlogical group of the parametershort_desctexta brief description of the parameterextra_desctextadditional, more detailed, information about the parametercontexttextcontext required to set the parameter's valuevartypetextparameter type (bool>, integer>,
real>, or string>)
sourcetextsource of the current parameter valuemin_valtextminimum allowed value of the parameter (NULL for nonnumeric
values)max_valtextmaximum allowed value of the parameter (NULL for nonnumeric
values)
The pg_settings view cannot be inserted into or
deleted from, but it can be updated. An UPDATE applied
to a row of pg_settings is equivalent to executing
the command on that named
parameter. The change only affects the value used by the current
session. If an UPDATE is issued within a transaction
that is later aborted, the effects of the UPDATE 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 UPDATE or
SET.
pg_statspg_stats
The view pg_stats provides access to
the information stored in the pg_statistic
catalog. This view allows access only to rows of
pg_statistic that correspond to tables the
user has permission to read, and therefore it is safe to allow public
read access to this view.
pg_stats is also designed to present the
information in a more readable format than the underlying catalog
— at the cost that its schema must be extended whenever new slot types
are defined for pg_statistic.
pg_stats> ColumnsNameTypeReferencesDescriptionschemanamenamepg_namespace.nspnamename of schema containing tabletablenamenamepg_class.relnamename of tableattnamenamepg_attribute.attnamename of the column described by this rownull_fracrealfraction of column entries that are nullavg_widthintegeraverage width in bytes of column's entriesn_distinctrealIf 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 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.
most_common_valsanyarrayA list of the most common values in the column. (NULL if
no values seem to be more common than any others.)most_common_freqsreal[]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 most_common_vals is.)
histogram_boundsanyarrayA list of values that divide the column's values into
groups of approximately equal population. The values in
most_common_vals>, if present, are omitted from this
histogram calculation. (This column is NULL if the column data type
does not have a <> operator or if the
most_common_vals> list accounts for the entire
population.)
correlationrealStatistical 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 <> operator.)
The maximum number of entries in the most_common_vals>
and histogram_bounds> arrays can be set on a
column-by-column basis using the ALTER TABLE SET STATISTICS>
command, or globally by setting the
runtime parameter.
pg_tablespg_tables
The view pg_tables provides access to
useful information about each table in the database.
pg_tables> ColumnsNameTypeReferencesDescriptionschemanamenamepg_namespace.nspnamename of schema containing tabletablenamenamepg_class.relnamename of tabletableownernamepg_shadow.usenamename of table's ownertablespacenamepg_tablespace.spcnamename of tablespace containing table (NULL if default for database)hasindexesbooleanpg_class.relhasindextrue if table has (or recently had) any indexeshasrulesbooleanpg_class.relhasrulestrue if table has ruleshastriggersbooleanpg_class.reltriggerstrue if table has triggers
pg_userpg_user
The view pg_user provides access to
information about database users. This is simply a publicly
readable view of
pg_shadow
that blanks out the password field.
pg_user> ColumnsNameTypeReferencesDescriptionusenamenameUser nameusesysidint4User ID (arbitrary number used to reference this user)usecreatedbboolUser may create databasesusesuperboolUser is a superuserusecatupdbool
User may update system catalogs. (Even a superuser may not do
this unless this column is true.)
passwdtextNot the password (always reads as ********>)valuntilabstimePassword expiry time (only used for password authentication)useconfigtext[]Session defaults for run-time configuration variables
pg_viewspg_views
The view pg_views provides access to
useful information about each view in the database.
pg_views> ColumnsNameTypeReferencesDescriptionschemanamenamepg_namespace.nspnamename of schema containing viewviewnamenamepg_class.relnamename of viewviewownernamepg_shadow.usenamename of view's ownerdefinitiontextview definition (a reconstructed SELECT query)