postgresql/doc/src/sgml/reference.sgml
Alvaro Herrera 7b504eb282 Implement multivariate n-distinct coefficients
Add support for explicitly declared statistic objects (CREATE
STATISTICS), allowing collection of statistics on more complex
combinations that individual table columns.  Companion commands DROP
STATISTICS and ALTER STATISTICS ... OWNER TO / SET SCHEMA / RENAME are
added too.  All this DDL has been designed so that more statistic types
can be added later on, such as multivariate most-common-values and
multivariate histograms between columns of a single table, leaving room
for permitting columns on multiple tables, too, as well as expressions.

This commit only adds support for collection of n-distinct coefficient
on user-specified sets of columns in a single table.  This is useful to
estimate number of distinct groups in GROUP BY and DISTINCT clauses;
estimation errors there can cause over-allocation of memory in hashed
aggregates, for instance, so it's a worthwhile problem to solve.  A new
special pseudo-type pg_ndistinct is used.

(num-distinct estimation was deemed sufficiently useful by itself that
this is worthwhile even if no further statistic types are added
immediately; so much so that another version of essentially the same
functionality was submitted by Kyotaro Horiguchi:
https://postgr.es/m/20150828.173334.114731693.horiguchi.kyotaro@lab.ntt.co.jp
though this commit does not use that code.)

Author: Tomas Vondra.  Some code rework by Álvaro.
Reviewed-by: Dean Rasheed, David Rowley, Kyotaro Horiguchi, Jeff Janes,
    Ideriha Takeshi
Discussion: https://postgr.es/m/543AFA15.4080608@fuzzy.cz
    https://postgr.es/m/20170320190220.ixlaueanxegqd5gr@alvherre.pgsql
2017-03-24 14:06:10 -03:00

287 lines
5.9 KiB
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<!-- doc/src/sgml/reference.sgml -->
<part id="reference">
<title>Reference</title>
<partintro>
<para>
The entries in this Reference are meant to provide in reasonable
length an authoritative, complete, and formal summary about their
respective subjects. More information about the use of
<productname>PostgreSQL</productname>, in narrative, tutorial, or
example form, can be found in other parts of this book. See the
cross-references listed on each reference page.
</para>
<para>
The reference entries are also available as traditional
<quote>man</quote> pages.
</para>
</partintro>
<reference id="sql-commands">
<title>SQL Commands</title>
<partintro>
<para>
This part contains reference information for the
<acronym>SQL</acronym> commands supported by
<productname>PostgreSQL</productname>. By <quote>SQL</quote> the
language in general is meant; information about the standards
conformance and compatibility of each command can be found on the
respective reference page.
</para>
</partintro>
&abort;
&alterAggregate;
&alterCollation;
&alterConversion;
&alterDatabase;
&alterDefaultPrivileges;
&alterDomain;
&alterEventTrigger;
&alterExtension;
&alterForeignDataWrapper;
&alterForeignTable;
&alterFunction;
&alterGroup;
&alterIndex;
&alterLanguage;
&alterLargeObject;
&alterMaterializedView;
&alterOperator;
&alterOperatorClass;
&alterOperatorFamily;
&alterPolicy;
&alterPublication;
&alterRole;
&alterRule;
&alterSchema;
&alterSequence;
&alterServer;
&alterStatistics;
&alterSubscription;
&alterSystem;
&alterTable;
&alterTableSpace;
&alterTSConfig;
&alterTSDictionary;
&alterTSParser;
&alterTSTemplate;
&alterTrigger;
&alterType;
&alterUser;
&alterUserMapping;
&alterView;
&analyze;
&begin;
&checkpoint;
&close;
&cluster;
&commentOn;
&commit;
&commitPrepared;
&copyTable;
&createAccessMethod;
&createAggregate;
&createCast;
&createCollation;
&createConversion;
&createDatabase;
&createDomain;
&createEventTrigger;
&createExtension;
&createForeignDataWrapper;
&createForeignTable;
&createFunction;
&createGroup;
&createIndex;
&createLanguage;
&createMaterializedView;
&createOperator;
&createOperatorClass;
&createOperatorFamily;
&createPolicy;
&createPublication;
&createRole;
&createRule;
&createSchema;
&createSequence;
&createServer;
&createStatistics;
&createSubscription;
&createTable;
&createTableAs;
&createTableSpace;
&createTSConfig;
&createTSDictionary;
&createTSParser;
&createTSTemplate;
&createTransform;
&createTrigger;
&createType;
&createUser;
&createUserMapping;
&createView;
&deallocate;
&declare;
&delete;
&discard;
&do;
&dropAccessMethod;
&dropAggregate;
&dropCast;
&dropCollation;
&dropConversion;
&dropDatabase;
&dropDomain;
&dropEventTrigger;
&dropExtension;
&dropForeignDataWrapper;
&dropForeignTable;
&dropFunction;
&dropGroup;
&dropIndex;
&dropLanguage;
&dropMaterializedView;
&dropOperator;
&dropOperatorClass;
&dropOperatorFamily;
&dropOwned;
&dropPolicy;
&dropPublication;
&dropRole;
&dropRule;
&dropSchema;
&dropSequence;
&dropServer;
&dropStatistics;
&dropSubscription;
&dropTable;
&dropTableSpace;
&dropTSConfig;
&dropTSDictionary;
&dropTSParser;
&dropTSTemplate;
&dropTransform;
&dropTrigger;
&dropType;
&dropUser;
&dropUserMapping;
&dropView;
&end;
&execute;
&explain;
&fetch;
&grant;
&importForeignSchema;
&insert;
&listen;
&load;
&lock;
&move;
&notify;
&prepare;
&prepareTransaction;
&reassignOwned;
&refreshMaterializedView;
&reindex;
&releaseSavepoint;
&reset;
&revoke;
&rollback;
&rollbackPrepared;
&rollbackTo;
&savepoint;
&securityLabel;
&select;
&selectInto;
&set;
&setConstraints;
&setRole;
&setSessionAuth;
&setTransaction;
&show;
&startTransaction;
&truncate;
&unlisten;
&update;
&vacuum;
&values;
</reference>
<reference id="reference-client">
<title>PostgreSQL Client Applications</title>
<partintro>
<para>
This part contains reference information for
<productname>PostgreSQL</productname> client applications and
utilities. Not all of these commands are of general utility; some
might require special privileges. The common feature of these
applications is that they can be run on any host, independent of
where the database server resides.
</para>
<para>
When specified on the command line, user and database names have
their case preserved &mdash; the presence of spaces or special
characters might require quoting. Table names and other identifiers
do not have their case preserved, except where documented, and
might require quoting.
</para>
</partintro>
&clusterdb;
&createdb;
&createuser;
&dropdb;
&dropuser;
&ecpgRef;
&pgBasebackup;
&pgbench;
&pgConfig;
&pgDump;
&pgDumpall;
&pgIsready;
&pgReceivewal;
&pgRecvlogical;
&pgRestore;
&psqlRef;
&reindexdb;
&vacuumdb;
</reference>
<reference id="reference-server">
<title>PostgreSQL Server Applications</title>
<partintro>
<para>
This part contains reference information for
<productname>PostgreSQL</productname> server applications and
support utilities. These commands can only be run usefully on the
host where the database server resides. Other utility programs
are listed in <xref linkend="reference-client">.
</para>
</partintro>
&initdb;
&pgarchivecleanup;
&pgControldata;
&pgCtl;
&pgResetwal;
&pgRewind;
&pgtestfsync;
&pgtesttiming;
&pgupgrade;
&pgwaldump;
&postgres;
&postmaster;
</reference>
</part>