On Fri, Jan 8, 2021 at 2:19 PM Thomas Munro <thomas.munro@gmail.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.