From 993a42ee2c73a1098845319b30811b5b7497f2f8 Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Fri, 21 Jan 2022 18:05:56 +0100 Subject: [PATCH v2 2/2] minor changes / rewordings --- doc/src/sgml/maintenance.sgml | 20 +++++++++--------- doc/src/sgml/perform.sgml | 2 -- doc/src/sgml/ref/analyze.sgml | 38 +++++++++++++++++++++++++---------- 3 files changed, 38 insertions(+), 22 deletions(-) diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml index b7c806cc906..2086dae61b2 100644 --- a/doc/src/sgml/maintenance.sgml +++ b/doc/src/sgml/maintenance.sgml @@ -291,11 +291,12 @@ - Tuples changed in partitions and inheritance children do not count towards + Tuples changed in partitions and inheritance children do not trigger analyze on the parent table. If the parent table is empty or rarely - changed, it may never be processed by autovacuum. It is necessary to - periodically manual run ANALYZE on the parent table to - keep the statistics of its table hierarchy up to date. + changed, it may never be processed by autovacuum, and the statistics for + the inheritance tree as a whole won't be collected. It is necessary to + run ANALYZE on the parent table manually, to keep + the statistics up to date. @@ -358,12 +359,13 @@ - The autovacuum daemon does not issue ANALYZE commands for - partitioned tables. Inheritance parents will only be analyzed if the + The autovacuum daemon may not issue ANALYZE commands + for partitioned tables. Inheritance parents will only be analyzed if the parent itself is changed - changes to child tables do not trigger - autoanalyze on the parent table. It is necessary to periodically run a - manual ANALYZE to keep the statistics of the table - hierarchy up to date. + autoanalyze on the parent table. If your queries require statistics on + parent relations for proper planning, it's necessary to periodically run + a manual ANALYZE on those tables to keep the statistics + up to date. diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml index b84853fd6ff..89ff58338e5 100644 --- a/doc/src/sgml/perform.sgml +++ b/doc/src/sgml/perform.sgml @@ -1765,11 +1765,9 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse; Run <command>ANALYZE</command> Afterwards - Whenever you have significantly altered the distribution of data within a table, running ANALYZE is strongly recommended. This includes bulk loading large amounts of data into the table. Running - ANALYZE (or VACUUM ANALYZE) 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 ea78f0d0387..1482fc2d4bb 100644 --- a/doc/src/sgml/ref/analyze.sgml +++ b/doc/src/sgml/ref/analyze.sgml @@ -250,18 +250,34 @@ ANALYZE [ VERBOSE ] [ table_and_columns - If the table being analyzed is partitioned, ANALYZE - 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.) + If the table being analyzed has one or more children, + ANALYZE 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 ANALYZE manually. + + + + For partitioned tables, ANALYZE gathers statistics by + sampling rows from all partitions; in addition, it will recurse into each + partition and update its statistics. Each leaf partition is analyzed only + once, even with multi-level partitioning. No statistics are collected for + the parent table (ignoring data from partitions), because with partitioning + it's guaranteed to be empty. + + + By constrast, if the table being analyzed has inheritance children, - ANALYZE 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. + ANALYZE gathers two sets of statistics: once on the rows + of the parent table only, and a second one including rows of both the parent + table and all child relations. This second set of statistics is needed when + planning queries that process the whole inheritance tree at once. The child + tables themselves are not individually analyzed in this case. -- 2.31.1