From: Tom Lane <tgl@sss.pgh.pa.us>
To: Chao Li <li.evan.chao@gmail.com>
cc: Dimitrios Apostolou <jimis@gmx.net>,
        Nathan Bossart <nathandbossart@gmail.com>,
        Thomas Munro <thomas.munro@gmail.com>,
        pgsql-hackers@lists.postgresql.org
Subject: Re: [PING] [PATCH v2] parallel pg_restore: avoid disk seeks when
 jumping short distance forward
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Comments: In-reply-to Chao Li <li.evan.chao@gmail.com>
	message dated "Tue, 14 Oct 2025 08:09:56 +0800"
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Date: Mon, 13 Oct 2025 20:36:07 -0400
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Chao Li <li.evan.chao@gmail.com> writes:
> I tested DEFAULT_IO_BUFFER_SIZE with 4K, 32K, 64K, 128K and 256K. Looks =
like increasing the buffer size doesn=E2=80=99t improve the performance si=
gnificantly. Actually, with the buffer size 64K, 128K and 256K, the test r=
esults are very close. I tested both with lz4 and none compression. I am n=
ot suggesting tuning the buffer size. These data are only for your referen=
ce.

Yeah, I would not expect straight pg_dump/pg_restore performance
to vary very much once the buffer size gets above not-too-many KB.
The thing we are really interested in here is how fast pg_restore
can skip over unwanted table data in a large archive file, and that
I believe should be pretty sensitive to block size.

You could measure that without getting into the complexities of
parallel restore if you make a custom-format dump of a few large
tables that does not have offset data in it, and then seeing how
fast is selective restore of just the last table.

			regards, tom lane