From 377f8d69d003a28cca5e34708d4570e75da55807 Mon Sep 17 00:00:00 2001 From: David Rowley Date: Mon, 31 Mar 2025 11:53:44 +1300 Subject: [PATCH v18] 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 Discussion: https://postgr.es/m/CAApHDvp738G75HfkKcfXaf3a8s%3D6mmtOLh46tMD0D2hAo1UCzA%40mail.gmail.com Backpatch-through: 12 --- 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 Subplans Removed property in the - EXPLAIN output. + EXPLAIN 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 EXPLAIN + output and not the ones referred to by the + Subplans Removed property. -- 2.40.1.windows.1