On Mon, 08 May 2006 19:08:59 +0100 Simon Riggs <[EMAIL PROTECTED]> wrote:
> On Fri, 2006-05-05 at 16:00 -0700, Mark Wong wrote: > > On Tue, 02 May 2006 10:52:38 +0100 > > Simon Riggs <[EMAIL PROTECTED]> wrote: > > > > > 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. > > > > I ran another few tests at the 600 scale factor just in case I was > > getting close to peaking at 500 warehouses. (Link above has updated > > data.) With wal_buffers set to 4096 the difference between 2048, 8192, > > and 32768 seem negligible. Some of the disks are at 90% utilization so > > perhaps I need to take a close look to make sure none of the other > > system resources are pegged. > > The profiles are fairly different though. > > Could you turn full_page_writes = off and do a few more tests? I think > the full page writes is swamping the xlog and masking the performance we > might see for normal small xlog writes. > I'd try XLOG_BLCKSZ = 4096 and 8192 to start with. Thanks. Ok, will get on it. > (Is VACUUM running at the start of these tests?) VACUUM is run immediately after the database tables are loaded. I've been reloading the database prior to each test. Mark ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
