diff options
-rw-r--r-- | doc/src/sgml/maintenance.sgml | 6 | ||||
-rw-r--r-- | doc/src/sgml/perform.sgml | 3 | ||||
-rw-r--r-- | doc/src/sgml/ref/analyze.sgml | 40 | ||||
-rw-r--r-- | doc/src/sgml/ref/pg_restore.sgml | 6 |
4 files changed, 41 insertions, 14 deletions
diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml index de7fd75e1c6..4b535809b63 100644 --- a/doc/src/sgml/maintenance.sgml +++ b/doc/src/sgml/maintenance.sgml @@ -817,6 +817,12 @@ analyze threshold = analyze base threshold + analyze scale factor * number of tu </programlisting> is compared to the total number of tuples inserted, updated, or deleted since the last <command>ANALYZE</command>. + For partitioned tables, inserts, updates and deletes on partitions + are counted towards this threshold; however, DDL + operations such as <literal>ATTACH</literal>, <literal>DETACH</literal> + and <literal>DROP</literal> are not, so running a manual + <command>ANALYZE</command> is recommended if the partition added or + removed contains a statistically significant volume of data. </para> <para> diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml index 89ff58338e5..ddd6c3ff3e0 100644 --- a/doc/src/sgml/perform.sgml +++ b/doc/src/sgml/perform.sgml @@ -1767,7 +1767,8 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse; <para> Whenever you have significantly altered the distribution of data within a table, running <link linkend="sql-analyze"><command>ANALYZE</command></link> is strongly recommended. This - includes bulk loading large amounts of data into the table. Running + includes bulk loading large amounts of data into the table as well as + attaching, detaching or dropping partitions. Running <command>ANALYZE</command> (or <command>VACUUM ANALYZE</command>) ensures that the planner has up-to-date statistics about the table. With no statistics or obsolete statistics, the planner might diff --git a/doc/src/sgml/ref/analyze.sgml b/doc/src/sgml/ref/analyze.sgml index c8fcebc1612..0879004b845 100644 --- a/doc/src/sgml/ref/analyze.sgml +++ b/doc/src/sgml/ref/analyze.sgml @@ -250,20 +250,38 @@ ANALYZE [ VERBOSE ] [ <replaceable class="parameter">table_and_columns</replacea </para> <para> - If the table being analyzed has one or more children, - <command>ANALYZE</command> will gather statistics twice: once on the - rows of the parent table only, and a second time on the rows of the - parent table with all of its children. This second set of statistics - is needed when planning queries that traverse the entire inheritance - tree. The autovacuum daemon, however, will only consider inserts or - updates on the parent table itself when deciding whether to trigger an - automatic analyze for that table. If that table is rarely inserted into - or updated, the inheritance statistics will not be up to date unless you - run <command>ANALYZE</command> manually. + If the table being analyzed is partitioned, <command>ANALYZE</command> + will gather statistics by sampling blocks randomly from its partitions; + in addition, it will recurse into each partition and update its statistics. + (However, in multi-level partitioning scenarios, each leaf partition + will only be analyzed once.) + By constrast, if the table being analyzed has inheritance children, + <command>ANALYZE</command> will gather statistics for it twice: + once on the rows of the parent table only, and a second time on the + rows of the parent table with all of its children. This second set of + statistics is needed when planning queries that traverse the entire + inheritance tree. The child tables themselves are not individually + analyzed in this case. </para> <para> - If any of the child tables are foreign tables whose foreign data wrappers + The autovacuum daemon counts inserts, updates and deletes in the + partitions to determine if auto-analyze is needed. However, adding + or removing partitions does not affect autovacuum daemon decisions, + so triggering a manual <command>ANALYZE</command> is recommended + when this occurs. + </para> + + <para> + Tuples changed in inheritance children do not count towards analyze + on the parent table. If the parent table is empty or rarely modified, + it may never be processed by autovacuum. It's necessary to + periodically run a manual <command>ANALYZE</command> to keep the + statistics of the table hierarchy up to date. + </para> + + <para> + If any of the child tables or partitions are foreign tables whose foreign data wrappers do not support <command>ANALYZE</command>, those child tables are ignored while gathering inheritance statistics. </para> diff --git a/doc/src/sgml/ref/pg_restore.sgml b/doc/src/sgml/ref/pg_restore.sgml index 93ea937ac8e..35cd56297c8 100644 --- a/doc/src/sgml/ref/pg_restore.sgml +++ b/doc/src/sgml/ref/pg_restore.sgml @@ -922,8 +922,10 @@ CREATE DATABASE foo WITH TEMPLATE template0; <para> Once restored, it is wise to run <command>ANALYZE</command> on each - restored table so the optimizer has useful statistics; see - <xref linkend="vacuum-for-statistics"/> and + restored table so the optimizer has useful statistics. + If the table is a partition or an inheritance child, it may also be useful + to analyze the parent to update statistics for the table hierarchy. + See <xref linkend="vacuum-for-statistics"/> and <xref linkend="autovacuum"/> for more information. </para> |