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Doc: add information about partition locking

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The documentation around locking of partitions for the executor startup
phase of run-time partition pruning wasn't clear about which partitions
were being locked.  Fix that.

Reviewed-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/CAApHDvp738G75HfkKcfXaf3a8s%3D6mmtOLh46tMD0D2hAo1UCzA%40mail.gmail.com
Backpatch-through: 13
This commit is contained in:
David Rowley 2025-04-02 14:02:44 +13:00
parent b3219c69fc
commit 121d774cae
1 changed files with 7 additions and 1 deletions
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8
doc/src/sgml/ddl.sgml
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@ -5075,7 +5075,13 @@ EXPLAIN SELECT count(*) FROM measurement WHERE logdate &gt;= DATE '2008-01-01';
It is possible to determine the number of partitions which were
removed during this phase by observing the
<quote>Subplans Removed</quote> property in the
<command>EXPLAIN</command> output.
<command>EXPLAIN</command> output. The query planner obtains locks for
all partitions which are part of the plan. However, when the executor
uses a cached plan, locks are only obtained on the partitions which
remain after partition pruning done during the initialization phase of
execution, i.e., the ones shown in the <command>EXPLAIN</command>
output and not the ones referred to by the
<quote>Subplans Removed</quote> property.
</para>
</listitem>