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Re: XLOG_BLCKSZ vs. wal_buffers table

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Mark Wong <markw(at)osdl(dot)org>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: XLOG_BLCKSZ vs. wal_buffers table
Date: 2006-06-05 09:42:36
Message-ID: 1149500556.2621.139.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, 2006-06-01 at 16:46 -0700, Mark Wong wrote:
> Simon Riggs wrote:
> > On Wed, 2006-05-10 at 09:55 -0700, Mark Wong wrote:
> >> Simon Riggs wrote:
> >>> 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, got data for XLOG_BLCKXZ at 4096, 8192, and 32768 with
> >> full_page_wirtes = off.  The new data is at the bottom of the page:
> >> 	http://developer.osdl.org/markw/pgsql/xlog_blcksz.html
> > 
> > What do you think is causing the step changes at 30+ and 60+ minutes on
> > these tests?
> 
> I took some time to start charting the sar data and to break down the 
> iostat data by tablespaces.  I've updated the web pages form the link 
> above.  Well, none of the charts helped me make any better guesses but 
> perhaps someone else will see something.
> 
> When I get back from my short break, I'm planning on taking a look at 
> Tau, a project from the University of Oregon 
> (http://www.cs.uoregon.edu/research/tau/home.php) that's capable of 
> breaking down profiles per process and gathering hardware counters.  I'm 
> hoping that will shed some light on the behavior.

Sounds useful. Let me know what you find.

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


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