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From: Hannu Krosing <[email protected]>
To: Dilip Kumar <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Nathan Bossart <[email protected]>
Subject: Re: Patch: dumping tables data in multiple chunks in pg_dump
Date: Mon, 24 Nov 2025 22:02:15 +0100
Message-ID: <CAMT0RQQPMj3=EZ-4z6qRs_TmBHoyv2VHAdMrfDuwa5ZUY6XtHQ@mail.gmail.com> (raw)
In-Reply-To: <CAFiTN-tV4jWKN75E5YLB-jSqb8j0E1PctiDjztv=ccfbe3YPmg@mail.gmail.com>
References: <CAMT0RQT_0qVxcTT6ycM20QUN-pEQ6iMLbz6gLWgLpeF0NmNOUA@mail.gmail.com>
	<CAFiTN-tV4jWKN75E5YLB-jSqb8j0E1PctiDjztv=ccfbe3YPmg@mail.gmail.com>

The expectation was that as chunking is useful mainly in case of
really huge tables the analyze should have been run "recently enough".

Maybe we should use pg_relation_size() in case we have already
determined that the table is large enough to warrant chunking? Maybe
at least 1/2 of the requested chunk size?

My reasoning was to not put too much extra load on pg_dump in case
chunking is not required. But of course we can use the presence of a
chunking request to decide to run pg_relation_size(), assuming the
overhead won't be too large in this case.


On Mon, Nov 17, 2025 at 5:15 AM Dilip Kumar <[email protected]> wrote:
>
> On Tue, Nov 11, 2025 at 9:00 PM Hannu Krosing <[email protected]> wrote:
> >
> > Attached is a patch that adds the ability to dump table data in multiple chunks.
> >
> > Looking for feedback at this point:
> >  1) what have I missed
> >  2) should I implement something to avoid single-page chunks
> >
> > The flag --huge-table-chunk-pages which tells the directory format
> > dump to dump tables where the main fork has more pages than this in
> > multiple chunks of given number of pages,
> >
> > The main use case is speeding up parallel dumps in case of one or a
> > small number of HUGE tables so parts of these can be dumped in
> > parallel.
> >
>
> +1 for the idea, I haven't done the detailed review but I was just
> going through the patch, I noticed that we use pg_class->relpages to
> identify whether to chunk the table or not, which should be fine but
> don't you think if we use direct size calculation function like
> pg_relation_size() we might get better idea and not dependent upon
> whether the stats are updated or not?  This will make chunking
> behavior more deterministic.
>
> --
> Regards,
> Dilip Kumar
> Google

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