Re: Spurious "apparent wraparound" via SimpleLruTruncate() rounding

From: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
To: Noah Misch <noah(at)leadboat(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Spurious "apparent wraparound" via SimpleLruTruncate() rounding
Date: 2021-01-10 06:44:14
Message-ID: ECF7E392-2BCF-442B-8A5A-F7B238D5E2B0@yandex-team.ru
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> 10 янв. 2021 г., в 03:15, Noah Misch <noah(at)leadboat(dot)com> написал(а):
>
> No; it deletes the most recent ~1B and leaves the older segments. An
> exception is multixact, as described in the commit message and the patch's
> change to a comment in TruncateMultiXact().

Thanks for clarification.
One more thing: retention point at 3/4 of overall space (half of wraparound) seems more or less random to me. Why not 5/8 or 9/16?

Can you please send revised patches with fixes?

Thanks!

Best regards, Andrey Borodin.

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