Re: fdatasync performance problem with large number of DB files

From: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
To: Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Michael Brown <michael(dot)brown(at)discourse(dot)org>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: fdatasync performance problem with large number of DB files
Date: 2021-03-17 03:02:58
Message-ID: CA+hUKG+NxM1VHeymXwz99PeJyc4yqCQsjs1tTGUztat+VpcKSw@mail.gmail.com
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On Tue, Mar 16, 2021 at 9:10 PM Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote:
> Thanks for the patch!
>
> + When set to <literal>fsync</literal>, which is the default,
> + <productname>PostgreSQL</productname> will recursively open and fsync
> + all files in the data directory before crash recovery begins.
>
> Isn't this a bit misleading? This may cause users to misunderstand that
> such fsync can happen only in the case of crash recovery.

If I insert the following extra sentence after that one, is it better?
"This applies whenever starting a database cluster that did not shut
down cleanly, including copies created with pg_basebackup."

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