| 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: | 2025-06-12 23:00:26 |
| Message-ID: | 5ed51587-5a24-4d79-e36e-927620d0e3a2@gmx.net |
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| Lists: | pgsql-hackers |
On Tue, 10 Jun 2025, Nathan Bossart wrote:
> So, fseeko() starts winning around 4096 bytes. On macOS, the differences
> aren't quite as dramatic, but 4096 bytes is the break-even point there,
> too. I imagine there's a buffer around that size somewhere...
>
> This doesn't fully explain the results you are seeing, but it does seem to
> validate the idea. I'm curious if you see further improvement with even
> lower thresholds (e.g., 8KB, 16KB, 32KB).
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?
Dimitris
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