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doc: simplify docs about analyze and inheritance/partitions 

Discussion: https://postgr.es/m/YxAqYijOsLzgLQgy@momjian.us

Backpatch-through: 10
This commit is contained in:
Bruce Momjian 2022-09-02 23:32:19 -04:00
parent 0f590f0064
commit adc15f49e6
1 changed files with 7 additions and 15 deletions
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doc/src/sgml/ref/analyze.sgml
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@ -251,12 +251,13 @@ ANALYZE [ VERBOSE ] [ <replaceable class="parameter">table_and_columns</replacea
</para> </para>
<para> <para>
If the table being analyzed has one or more children, If the table being analyzed has inheritance children,
<command>ANALYZE</command> will gather statistics twice: once on the <command>ANALYZE</command> gathers two sets of statistics: one on the rows
rows of the parent table only, and a second time on the rows of the of the parent table only, and a second including rows of both the parent
parent table with all of its children. This second set of statistics table and all of its children. This second set of statistics is needed when
is needed when planning queries that traverse the entire inheritance planning queries that process the inheritance tree as a whole. The child
tree. The autovacuum daemon, however, will only consider inserts or tables themselves are not individually analyzed in this case.
The autovacuum daemon, however, will only consider inserts or
updates on the parent table itself when deciding whether to trigger an updates on the parent table itself when deciding whether to trigger an
automatic analyze for that table. If that table is rarely inserted into 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 or updated, the inheritance statistics will not be up to date unless you
@ -272,15 +273,6 @@ ANALYZE [ VERBOSE ] [ <replaceable class="parameter">table_and_columns</replacea
partitioning it's guaranteed to be empty. partitioning it's guaranteed to be empty.
</para> </para>
<para>
By contrast, if the table being analyzed has inheritance children,
<command>ANALYZE</command> 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.
</para>
<para> <para>
The autovacuum daemon does not process partitioned tables, nor does it The autovacuum daemon does not process partitioned tables, nor does it
process inheritance parents if only the children are ever modified. process inheritance parents if only the children are ever modified.