This patch makes a few minor improvements to the docs: make the
<varname> conventions more consistent, and improve the ANALYZE ref page. Neil Conway
This commit is contained in:
Bruce Momjian
parent
64a7b58aa0
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8e27be4310
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/perform.sgml,v 1.31 2003/08/31 17:32:19 petere Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/perform.sgml,v 1.32 2003/09/11 17:31:45 momjian Exp $
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-->
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<chapter id="performance-tips">
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@ -603,7 +603,7 @@ SELECT * FROM a, b, c WHERE a.id = b.id AND b.ref = c.id;
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<productname>PostgreSQL</productname> planner will switch from exhaustive
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search to a <firstterm>genetic</firstterm> probabilistic search
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through a limited number of possibilities. (The switch-over threshold is
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set by the <varname>geqo_threshold</varname> run-time
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set by the <varname>GEQO_THRESHOLD</varname> run-time
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parameter.)
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The genetic search takes less time, but it won't
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necessarily find the best possible plan.
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/plpgsql.sgml,v 1.22 2003/09/03 22:17:07 petere Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/plpgsql.sgml,v 1.23 2003/09/11 17:31:45 momjian Exp $
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-->
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<chapter id="plpgsql">
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@ -1350,7 +1350,7 @@ SELECT * FROM some_func();
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allow users to allow users to define set-returning functions
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that do not have this limitation. Currently, the point at
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which data begins being written to disk is controlled by the
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<varname>sort_mem</> configuration variable. Administrators
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<varname>SORT_MEM</> configuration variable. Administrators
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who have sufficient memory to store larger result sets in
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memory should consider increasing this parameter.
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</para>
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/analyze.sgml,v 1.14 2003/09/09 18:28:52 tgl Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/analyze.sgml,v 1.15 2003/09/11 17:31:45 momjian Exp $
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PostgreSQL documentation
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-->
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@ -28,10 +28,10 @@ ANALYZE [ VERBOSE ] [ <replaceable class="PARAMETER">table</replaceable> [ (<rep
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<title>Description</title>
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<para>
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<command>ANALYZE</command> collects statistics about the contents of
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tables in the database, and stores the results in
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the system table <literal>pg_statistic</literal>. Subsequently,
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the query planner uses the statistics to help determine the most efficient
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<command>ANALYZE</command> collects statistics about the contents
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of tables in the database, and stores the results in the system
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table <literal>pg_statistic</literal>. Subsequently, the query
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planner uses these statistics to help determine the most efficient
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execution plans for queries.
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</para>
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@ -90,49 +90,56 @@ ANALYZE [ VERBOSE ] [ <replaceable class="PARAMETER">table</replaceable> [ (<rep
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</para>
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<para>
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Unlike <command>VACUUM FULL</command>,
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<command>ANALYZE</command> requires
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only a read lock on the target table, so it can run in parallel with
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other activity on the table.
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Unlike <command>VACUUM FULL</command>, <command>ANALYZE</command>
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requires only a read lock on the target table, so it can run in
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parallel with other activity on the table.
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</para>
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<para>
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For large tables, <command>ANALYZE</command> takes a random sample of the
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table contents, rather than examining every row. This allows even very
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large tables to be analyzed in a small amount of time. Note, however,
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that the statistics are only approximate, and will change slightly each
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time <command>ANALYZE</command> is run, even if the actual table contents
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did not change. This may result in small changes in the planner's
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estimated costs shown by <command>EXPLAIN</command>.
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The statistics collected by <command>ANALYZE</command> usually
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include a list of some of the most common values in each column and
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a histogram showing the approximate data distribution in each
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column. One or both of these may be omitted if
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<command>ANALYZE</command> deems them uninteresting (for example,
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in a unique-key column, there are no common values) or if the
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column data type does not support the appropriate operators. There
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is more information about the statistics in <xref
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linkend="maintenance">.
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</para>
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<para>
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The collected statistics usually include a list of some of the most common
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values in each column and a histogram showing the approximate data
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distribution in each column. One or both of these may be omitted if
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<command>ANALYZE</command> deems them uninteresting (for example, in
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a unique-key column, there are no common values) or if the column
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data type does not support the appropriate operators. There is more
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information about the statistics in <xref linkend="maintenance">.
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For large tables, <command>ANALYZE</command> takes a random sample
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of the table contents, rather than examining every row. This
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allows even very large tables to be analyzed in a small amount of
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time. Note, however, that the statistics are only approximate, and
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will change slightly each time <command>ANALYZE</command> is run,
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even if the actual table contents did not change. This may result
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in small changes in the planner's estimated costs shown by
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<command>EXPLAIN</command>. In rare situations, this
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non-determinism will cause the query optimizer to choose a
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different query plan between runs of <command>ANALYZE</command>. To
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avoid this, raise the amount of statistics collected by
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<command>ANALYZE</command>, as described below.
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</para>
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<para>
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The extent of analysis can be controlled by adjusting the
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<literal>default_statistics_target</> parameter variable, or on a
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column-by-column basis by setting the per-column
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statistics target with <command>ALTER TABLE ... ALTER COLUMN ... SET
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STATISTICS</command> (see
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<xref linkend="sql-altertable" endterm="sql-altertable-title">). The
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target value sets the maximum number of entries in the most-common-value
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list and the maximum number of bins in the histogram. The default
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target value is 10, but this can be adjusted up or down to trade off
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accuracy of planner estimates against the time taken for
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<command>ANALYZE</command> and the amount of space occupied
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in <literal>pg_statistic</literal>.
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In particular, setting the statistics target to zero disables collection of
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statistics for that column. It may be useful to do that for columns that
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are never used as part of the <literal>WHERE</>, <literal>GROUP BY</>, or <literal>ORDER BY</> clauses of
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queries, since the planner will have no use for statistics on such columns.
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<varname>DEFAULT_STATISTICS_TARGET</varname> parameter variable, or
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on a column-by-column basis by setting the per-column statistics
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target with <command>ALTER TABLE ... ALTER COLUMN ... SET
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STATISTICS</command> (see <xref linkend="sql-altertable"
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endterm="sql-altertable-title">). The target value sets the
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maximum number of entries in the most-common-value list and the
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maximum number of bins in the histogram. The default target value
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is 10, but this can be adjusted up or down to trade off accuracy of
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planner estimates against the time taken for
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<command>ANALYZE</command> and the amount of space occupied in
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<literal>pg_statistic</literal>. In particular, setting the
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statistics target to zero disables collection of statistics for
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that column. It may be useful to do that for columns that are
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never used as part of the <literal>WHERE</>, <literal>GROUP BY</>,
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or <literal>ORDER BY</> clauses of queries, since the planner will
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have no use for statistics on such columns.
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</para>
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<para>
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_user.sgml,v 1.28 2003/09/09 18:28:53 tgl Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_user.sgml,v 1.29 2003/09/11 17:31:45 momjian Exp $
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PostgreSQL documentation
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-->
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@ -98,7 +98,7 @@ where <replaceable class="PARAMETER">option</replaceable> can be:
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These key words control whether the password is stored
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encrypted in the system catalogs. (If neither is specified,
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the default behavior is determined by the configuration
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parameter <varname>password_encryption</varname>.) If the
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parameter <varname>PASSWORD_ENCRYPTION</varname>.) If the
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presented password string is already in MD5-encrypted format,
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then it is stored encrypted as-is, regardless of whether
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<literal>ENCRYPTED</> or <literal>UNENCRYPTED</> is specified
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/postmaster.sgml,v 1.37 2003/08/31 17:32:24 petere Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/postmaster.sgml,v 1.38 2003/09/11 17:31:45 momjian Exp $
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PostgreSQL documentation
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-->
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@ -376,7 +376,7 @@ PostgreSQL documentation
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<listitem>
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<para>
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Default value of the <literal>datestyle</literal> run-time
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Default value of the <varname>DATESTYLE</varname> run-time
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parameter. (The use of this environment variable is deprecated.)
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</para>
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</listitem>
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@ -563,7 +563,7 @@ PostgreSQL documentation
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<prompt>$</prompt> <userinput>postmaster -c sort_mem=1234</userinput>
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<prompt>$</prompt> <userinput>postmaster --sort-mem=1234</userinput>
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</screen>
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Either form overrides whatever setting might exist for <literal>sort_mem</>
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Either form overrides whatever setting might exist for <varname>SORT_MEM</>
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in <filename>postgresql.conf</>. Notice that underscores in parameter
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names can be written as either underscore or dash on the command line.
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</para>
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/reset.sgml,v 1.22 2003/09/09 18:28:53 tgl Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/reset.sgml,v 1.23 2003/09/11 17:31:45 momjian Exp $
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PostgreSQL documentation
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-->
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@ -85,14 +85,14 @@ SET <replaceable class="parameter">parameter</replaceable> TO DEFAULT
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<title>Examples</title>
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<para>
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Set <varname>datestyle</> to its default value:
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Set <varname>DATESTYLE</> to its default value:
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<screen>
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RESET datestyle;
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</screen>
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</para>
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<para>
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Set <varname>geqo</> to its default value:
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Set <varname>GEQO</> to its default value:
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<screen>
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RESET geqo;
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</screen>
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