Re: Two fsync related performance issues?

Thanks for the replies.

On Tue, May 12, 2020 at 2:04 PM Michael Paquier <michael(at)paquier(dot)xyz> wrote:

> On Tue, May 12, 2020 at 12:55:37PM +0900, Fujii Masao wrote:
> > On 2020/05/12 9:42, Paul Guo wrote:
> >> 1. StartupXLOG() does fsync on the whole data directory early in
> >> the crash recovery. I'm wondering if we could skip some
> >> directories (at least the pg_log/, table directories) since wal,
> >> etc could ensure consistency.
> >
> > I agree that we can skip log directory but I'm not sure if skipping
> > table directory is really safe. Also ISTM that we can skip the
> directories
> > that those contents are removed or zeroed during recovery,
> > for example, pg_snapshots, pg_substrans, etc.
>
> Basically excludeDirContents[] as of basebackup.c.
>

table directories & wal fsync probably dominates the fsync time. Do we
know any possible real scenario that requires table directory fsync?