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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dimitrios Apostolou <jimis@gmx.net>
Cc: Chao Li <li.evan.chao@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: [PATCH v4] parallel pg_restore: avoid disk seeks when jumping short distance forward
Date: Mon, 20 Oct 2025 18:23:27 -0400
Message-ID: <382528.1760999007@sss.pgh.pa.us> (raw)
In-Reply-To: <7B29E5B2-94DC-48ED-A1F3-247BCE5A2329@gmx.net>
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Dimitrios Apostolou <jimis@gmx.net> writes:
> Thanks for the extensive testing! Did you see the same syscall pattern in strace output, as I did?

Yes, I did look at that, and it's the same as you saw:
HEAD repeats

        read(4k)
        lseek(~128k forward)

which is to be expected if we have to read data block headers
that are ~128K apart; while patched repeats

         read(4k)
         read(~128k)

which is a bit odd in itself, why isn't it merging the reads better?

> I was using an HDD,

Ah.  Your original message mentioned NVMe so I was assuming you
were also looking at solid-state drives.  I can imagine that
seeking is more painful on HDDs ...

			regards, tom lane





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