From: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
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To: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Default wal_sync_method on FreeBSD |
Date: | 2021-02-15 03:28:08 |
Message-ID: | CA+hUKG+z5hkmvFSA-9e7Xi8Gv4+uhxMMaU4-dXJ-iOtD9fZ9NA@mail.gmail.com |
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On Fri, Jan 8, 2021 at 2:19 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> The system header change has one interesting consequence for existing
> releases of PostgreSQL, though: xlogdefs.h now sees that there is an
> O_DSYNC macro that is distinct from O_SYNC, and defaults to
> wal_sync_method=open_datasync. That's not a great default setting,
> because it gets you O_DIRECT | O_DSYNC, which performs terribly when
> you're writing 8KB blocks on UFS's default 32KB logical block size (it
> triggers read-before-write, quite visibly destroying performance with
> eg pg_test_fsync), and for all I know, it might even not work at all
> on some other file systems. I suspect it might come out very slightly
> ahead on a UFS filesystem created with 8KB blocks, but in any case,
> that seems like something you should have to opt in to, as you do on
> Linux.
Done.
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