postgres.git / summary / log / commit / refs
commit 121d774caea4c93c8b36fb20a17ef774e60894d6
Author: David Rowley <drowley@postgresql.org>
Date: Wed Apr 02 01:02:44 2025 +0000
First released in: 18.0, 13.21, 14.18, 15.13, 16.9, 17.5
Doc: add information about partition locking
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
doc/src/sgml/ddl.sgml | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index cdb1a07e9d3..d2082b7e88e 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -5075,7 +5075,13 @@ EXPLAIN SELECT count(*) FROM measurement WHERE logdate >= 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>
[parent: b3219c69fc1e]