Re: pgsql: Doc: add information about partition locking - Mailing list pgsql-committers

On Fri, Mar 27, 2026 at 4:09 PM Amit Langote <amitlangote09@gmail.com> wrote:
> Hi David,
>
> On Wed, Apr 2, 2025 at 10:03 AM David Rowley <drowley@postgresql.org> 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 <tndrwang@gmail.com>
> > 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