Re: WAL format and API changes (9.5)

On 2014-10-06 14:19:39 +0300, Heikki Linnakangas wrote:
> On 10/06/2014 04:42 AM, Michael Paquier wrote:
> >On Fri, Oct 3, 2014 at 9:51 PM, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>
> >wrote:
> >>So I now have a refactoring patch ready that I'd like to commit (the
> >attached two patches together), but to be honest, I have no idea why the
> >second patch is so essential to performance.
> >Thanks. I did some more tests with master, master+patch1, master+patch1+CRC
> >refactoring, but I am not able to see any performance difference with
> >pgbench (--no-vacuum, -t) and the test suite you provided, just some noise
> >that barely changed performance.
>
> Thanks for the confirmation. I'm really going crazy with benchmarking this.
> Sometimes I see a big difference, the next day it's gone.

A usual suspect for this is turbo mode and power control. It often
already helps to disable the latter to get much more reproducible
benchmark results.

> Barring objections, I'll commit this, and then continue benchmarking the
> second patch with the WAL format and API changes.

I'd like to have a look at it beforehand. I've not yet really looked,
but on a quick readthrough XLogInsertRecData() staying in xlog.c doesn't
make me happy...

Greetings,

Andres Freund