Horton

Re: Wierd context-switching issue on Xeon

Josh Berkus <josh@agliodbs.com>

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From: Josh Berkus <josh@agliodbs.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, Bruce Momjian <pgman@candle.pha.pa.us>
Cc: pg@fastcrypt.com, Robert Creager <Robert_Creager@LogicalChaos.org>, Dirk_Lutzebäck <lutzeb@aeccom.com>, ohp@pyrenet.fr, Joe Conway <mail@joeconway.com>, "scott.marlowe" <scott.marlowe@ihs.com>, pgsql-performance@postgresql.org, Neil Conway <neilc@samurai.com>
Date: 2004-05-20T21:52:07Z
Lists: pgsql-performance 
Guys,
 
> Oh, you wanted a fix?  That seems harder :-(.  AFAICS we need a redesign
> that causes less load on the BufMgrLock.

FWIW, we've been pursuing two routes of quick patch fixes.

1) Dave Cramer and I have been testing setting varying rates of spin_delay in 
an effort to find a "sweet spot" that the individual system seems to like.   
This has been somewhat delayed by my illness.

2) The OSDL folks have been trying various patches to use Linux 2.6 Futexes in 
place of semops (if I have that right) which, if successful, would produce a 
linux-specific fix.   However, they haven't yet come up wiith a version of 
the patch which is stable.

I'm really curious, BTW, about how all of Jan's changes to buffer usage in 7.5 
affect this issue.   Has anyone tested it on a recent snapshot?

-- 
-Josh Berkus
 Aglio Database Solutions
 San Francisco