Re: [PING] [PATCH v2] parallel pg_restore: avoid disk seeks when jumping short distance forward

From: Dimitrios Apostolou <jimis(at)gmx(dot)net>
To: Nathan Bossart <nathandbossart(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: [PING] [PATCH v2] parallel pg_restore: avoid disk seeks when jumping short distance forward
Date: 2025-07-23 21:54:44
Message-ID: n212516n-7962-9060-7oo5-rpn814q82p4r@tzk.arg
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Hi Nathan, I've noticed you've set yourself as a reviewer of this patch
in the commitfest. I appreciate it, but you might want to combine it
with another simple patch [1] that speeds up the same part of
pg_restore: the initial full scan on TOC-less archives.

[1] https://commitfest.postgresql.org/patch/5817/

On Saturday 2025-06-14 00:04, Nathan Bossart wrote:
>
> On Fri, Jun 13, 2025 at 01:00:26AM +0200, Dimitrios Apostolou wrote:
>> By the way, I might have set the threshold to 1MB in my program, but
>> lowering it won't show a difference in my test case, since the lseek()s I
>> was noticing before the patch were mostly 8-16KB forward. Not sure what is
>> the defining factor for that. Maybe the compression algorithm, or how wide
>> the table is?
>
> I may have missed it, but could you share what the strace looks like with
> the patch applied?

I hope you've seen my response here, with special focus on the small
block size that both compressed and uncompressed custom format archives
have.

I have been needing to pg_restore 10TB TOC-less dumps recently, and it's
a pain to do the full scan, even with both of my patches applied.

Maybe the block size could be a command line option of pg_dump, so that
one could set it to sizes like 100MB, which sounds like a normal block
from the perspective of a 10TB gigantic dump.

Regards,
Dimitris

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