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help / color / mirror / Atom feedFrom: David Rowley <[email protected]>
To: Tender Wang <[email protected]>
Cc: PostgreSQL Developers <[email protected]>
Subject: Re: Add mention in docs about locking all partitions for generic plans
Date: Mon, 31 Mar 2025 12:19:38 +1300
Message-ID: <CAApHDvogvzANoTOCyXUWgEuPFx1nT6S63aAN0bDRSJ=TaGBWew@mail.gmail.com> (raw)
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<CAHewXNm2iCGgi4_+WCJ-nnBPKB1q_uXJzSPArHWV_SaDb=gV+Q@mail.gmail.com>
On Mon, 24 Mar 2025 at 22:19, Tender Wang <[email protected]> wrote:
>> Maybe I was wrong about writing nothing in master's docs. It might
>> still be important to detail this. I don't know the best way to phrase
>> that, but maybe something along the lines of: "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.".
>>
>> Any opinions?
>
> The above sentence looks good to me.
Thanks for looking.
I've attached the master and the <= v17 in patch form. Also, the
compiled HTML for ease of review.
I'll push these in the next few days unless anyone else wants to voice
their opinions.
David
Attachments:
[application/x-zip-compressed] ddl-partitioning.html.zip (31.0K, ../CAApHDvogvzANoTOCyXUWgEuPFx1nT6S63aAN0bDRSJ=TaGBWew@mail.gmail.com/2-ddl-partitioning.html.zip)
download
[application/octet-stream] v17-0001-Doc-add-information-about-partition-locking.patch (1.4K, ../CAApHDvogvzANoTOCyXUWgEuPFx1nT6S63aAN0bDRSJ=TaGBWew@mail.gmail.com/3-v17-0001-Doc-add-information-about-partition-locking.patch)
download | inline diff:
From 02c0192816f5247a5fc71a5ad59f28306fb56080 Mon Sep 17 00:00:00 2001
From: David Rowley <[email protected]>
Date: Mon, 31 Mar 2025 12:02:55 +1300
Subject: [PATCH v17] 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: 12
---
doc/src/sgml/ddl.sgml | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index c150dd217f9..bef12758711 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -4986,7 +4986,9 @@ 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.
+ <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>
--
2.40.1.windows.1
[application/octet-stream] v18-0001-Doc-add-information-about-partition-locking.patch (1.6K, ../CAApHDvogvzANoTOCyXUWgEuPFx1nT6S63aAN0bDRSJ=TaGBWew@mail.gmail.com/4-v18-0001-Doc-add-information-about-partition-locking.patch)
download | inline diff:
From 377f8d69d003a28cca5e34708d4570e75da55807 Mon Sep 17 00:00:00 2001
From: David Rowley <[email protected]>
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 <[email protected]>
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
<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>
--
2.40.1.windows.1
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