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Re: XLogInsert scaling, revisited

Ants Aasma <ants@cybertec.at>

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From: Ants Aasma <ants@cybertec.at>
To: Heikki Linnakangas <hlinnakangas@vmware.com>
Cc: Andres Freund <andres@2ndquadrant.com>, Jeff Janes <jeff.janes@gmail.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2013-07-08T10:21:17Z
Lists: pgsql-hackers 
On Mon, Jul 8, 2013 at 12:16 PM, Heikki Linnakangas
<hlinnakangas@vmware.com> wrote:
> Ok, I've committed this patch now. Finally, phew!

Fantastic work!

> I simplified the handling of xlogInsertingAt per discussion, and added the
> memory barrier to GetXLogBuffer(). I ran again the pgbench tests I did
> earlier with the now-committed version of the patch (except for some comment
> changes). The results are here:

I can't see a reason why a full memory barrier is needed at
GetXLogBuffer, we just need to ensure that we read the content of the
page after we check the end pointer from xlblocks. A read barrier is
enough here unless there is some other undocumented interaction. I
don't think it matters for performance, but it seems like good
practice to have the barriers exactly matching the documentation.

Regards,
Ants Aasma
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