From c237d91ec258ebbf24ebd3a38e139777582817f6 Mon Sep 17 00:00:00 2001 From: Justin Pryzby Date: Thu, 22 Jul 2021 16:06:18 -0500 Subject: [PATCH] documentation deficiencies for ANALYZE of partitioned tables This is partially extracted from 1b5617eb844cd2470a334c1d2eec66cf9b39c41a, which was reverted. --- doc/src/sgml/maintenance.sgml | 29 +++++++++++++++++++++++++++++ doc/src/sgml/ref/analyze.sgml | 32 +++++++++++++++++++++++++++++--- 2 files changed, 58 insertions(+), 3 deletions(-) diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml index 36f975b1e5b..34d72dba784 100644 --- a/doc/src/sgml/maintenance.sgml +++ b/doc/src/sgml/maintenance.sgml @@ -290,6 +290,15 @@ to meaningful statistical changes. + + 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, 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 in order to + keep the statistics up to date. + + As with vacuuming for space recovery, frequent updates of statistics are more useful for heavily-updated tables than for seldom-updated @@ -347,6 +356,19 @@ ANALYZE commands on those tables on a suitable schedule. + + + + The autovacuum daemon does 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. If your queries require statistics on + parent tables for proper planning, it is necessary to periodically run + a manual ANALYZE on those tables to keep the statistics + up to date. + + + @@ -819,6 +841,13 @@ analyze threshold = analyze base threshold + analyze scale factor * number of tu since the last ANALYZE. + + Partitioned tables are not processed by autovacuum. Statistics + should be collected by running a manual ANALYZE when it is + first populated, and again whenever the distribution of data in its + partitions changes significantly. + + Temporary tables cannot be accessed by autovacuum. Therefore, appropriate vacuum and analyze operations should be performed via diff --git a/doc/src/sgml/ref/analyze.sgml b/doc/src/sgml/ref/analyze.sgml index c423aeeea5e..8268ba87f63 100644 --- a/doc/src/sgml/ref/analyze.sgml +++ b/doc/src/sgml/ref/analyze.sgml @@ -263,9 +263,35 @@ ANALYZE [ VERBOSE ] [ table_and_columns - If any of the child tables are foreign tables whose foreign data wrappers - do not support ANALYZE, those child tables are ignored while - gathering inheritance statistics. + 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 + only the parent table (without data from its partitions), because with + partitioning it's guaranteed to be empty. + + + + By constrast, if the table being analyzed has inheritance children, + ANALYZE gathers two sets of statistics: one on the rows + of the parent table only, and a second including rows of both the parent + table and all of its children. This second set of statistics is needed when + planning queries that process the inheritance tree as a whole. The child + tables themselves are not individually analyzed in this case. + + + + The autovacuum daemon does not process partitioned tables, nor does it + process inheritance parents if only the children are ever modified. + It is usually necessary to periodically run a manual + ANALYZE to keep the statistics of the table hierarchy + up to date. + + + + If any child tables or partitions are foreign tables whose foreign + data wrappers do not support ANALYZE, those tables are + ignored while gathering inheritance statistics. -- 2.17.1