On Friday 15 February 2008 06:29, Greg Smith wrote:
> PostgreSQL only uses direct I/O for writing to the WAL; everything else
> goes through the regular OS buffer cache unless you force it to do
> otherwise at the OS level (like some Solaris setups do with
> forcedirectio).
Also, note that even when direct I/O is available, most users and benchmark
tests have reported that having PostgreSQL "take over" the entire cache is
not a net performance gain. I believe this is mostly because our I/O and
caching code aren't designed for this kind of operation.
I believe that MyEmma had a different experience on their workload, though.
--
Josh Berkus
PostgreSQL @ Sun
San Francisco