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help / color / mirror / Atom feedFrom: Amit Langote <[email protected]>
To: David Rowley <[email protected]>
Cc: [email protected]
Subject: Re: pgsql: Doc: add information about partition locking
Date: Fri, 27 Mar 2026 16:15:32 +0900
Message-ID: <CA+HiwqG=_5tSA-FWJ_Fzs2xWkxOUxFhzDs2KaDCUDHQOKe41ew@mail.gmail.com> (raw)
In-Reply-To: <CA+HiwqFT0fPPoYBr0iUFWNB-Og7bEXB9hB=6ogk_qD9=OM8Vbw@mail.gmail.com>
References: <[email protected]>
<CA+HiwqFT0fPPoYBr0iUFWNB-Og7bEXB9hB=6ogk_qD9=OM8Vbw@mail.gmail.com>
On Fri, Mar 27, 2026 at 4:09 PM Amit Langote <[email protected]> wrote:
> Hi David,
>
> On Wed, Apr 2, 2025 at 10:03 AM David Rowley <[email protected]> wrote:
> >
> > 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 <[email protected]>
> > Discussion: https://postgr.es/m/CAApHDvp738G75HfkKcfXaf3a8s%3D6mmtOLh46tMD0D2hAo1UCzA%40mail.gmail.com
> > Backpatch-through: 13
> >
> > Branch
> > ------
> > master
> >
> > Details
> > -------
> > https://git.postgresql.org/pg/commitdiff/121d774caea4c93c8b36fb20a17ef774e60894d6
>
> - <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>
>
> This text was correct when committed, but became incorrect after I
> reverted 525392d57 in May 2025. Sorry for not catching it sooner.
>
> I think we should change the text in both master and REL_18_STABLE to
> match what you added in the older branches. I can change it back to
> this when we get pruning-aware locking again.
Will apply the attached.
--
Thanks, Amit Langote
Attachments:
[application/octet-stream] v1-0001-Doc-fix-stale-text-about-partition-locking-with-c.patch (1.9K, 2-v1-0001-Doc-fix-stale-text-about-partition-locking-with-c.patch)
download | inline diff:
From 6cca1e1b7f2945db63863e236ca62a1d6291d493 Mon Sep 17 00:00:00 2001
From: Amit Langote <[email protected]>
Date: Fri, 27 Mar 2026 16:12:23 +0900
Subject: [PATCH v1] Doc: fix stale text about partition locking with cached
plans
Commit 121d774caea added text to master describing pruning-aware
locking behavior introduced by 525392d57. That behavior was
reverted in May 2025, making the text incorrect. Replace it with
the text used in back branches, which correctly describes current
behavior: pruned partitions are still locked at the beginning of
execution.
Discussion: https://postgr.es/m/CA+HiwqFT0fPPoYBr0iUFWNB-Og7bEXB9hB=6ogk_qD9=OM8Vbw@mail.gmail.com
---
doc/src/sgml/ddl.sgml | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 8421ecace1b..bd8cb461cba 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -5416,13 +5416,9 @@ 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. 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.
+ <command>EXPLAIN</command> output. It's important to note that any
+ partitions removed by the partition pruning done at this stage are
+ still locked at the beginning of execution.
</para>
</listitem>
--
2.47.3
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Subject: Re: pgsql: Doc: add information about partition locking
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