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: 2025-06-14 16:01:13
Message-ID: f99e9774-da49-60f0-20e0-b97d9f12a04e@gmx.net
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On Fri, 13 Jun 2025, 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?

read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 12288) = 12288
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 12288) = 12288
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 12288) = 12288
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 12288) = 12288
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096

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