Re: Advice configuring ServeRAID 8k for performance

Andres Freund wrote:
> Or use -o sync. Or configure a ridiciuosly low dirty_memory amount
> (which has a problem on large systems because 1% can still be too
> much. Argh.)...
>

-o sync completely trashes performance, and trying to set the
dirty_ratio values to even 1% doesn't really work due to things like the
"congestion avoidance" code in the kernel.  If you sync a lot more
often, which putting the WAL on the same disk as the database
accidentally does for you, that works surprisingly well at avoiding this
whole class of problem on ext3.  A really good solution is going to take
a full rewrite of the PostgreSQL checkpoint logic though, which will get
sorted out during 9.1 development.  (cue dramatic foreshadowing music here)

--
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com   www.2ndQuadrant.us