Re: XLOG_BLCKSZ vs. wal_buffers table

On Sun, 2006-04-30 at 22:14 -0700, Mark Wong wrote:
> I would have gotten this out sooner but I'm having trouble with our
> infrastructure.  Here's a link to a table of data I've started putting
> together regarding XLOG_BLCKSZ and wal_buffers on a 4-way Opteron
> system:
>     http://developer.osdl.org/markw/pgsql/xlog_blcksz.html
> 
> There are a couple of holes in the table but I think it shows enough
> evidence to say that with dbt2 having a larger XLOG_BLCKSZ improves the
> overall throughput of the test.
> 
> I'm planning on continuing to increase XLOG_BLCKSZ and wal_buffers to
> determine when the throughput starts to level out or drop off, and then
> start experimenting with varying BLCKSZ.  Let me know if there are other
> things that would be more interesting to experiment with first.

IMHO you should be testing with higher wal_buffers settings. ISTM likely
that the improved performance is due to there being more buffer space,
rather than actually improving I/O. Setting wal_buffers to something
fairly high say 4096 would completely remove any such effect so we are
left with a view on the I/O.

--  Simon Riggs              EnterpriseDB   http://www.enterprisedb.com