On 19/01/10 10:50, fkater@xxxxxxxxxxxxxx wrote:
However, the deeper question is (sounds ridiculous): Why am
I I/O bound *this much* here. To recall: The write
performance in pg is about 20-25% of the worst case serial
write performance of the disk (and only about 8-10% of the
best disk perf) even though pg_xlog (WAL) is moved to
another disk, only 10 simple INSERT commands, a simple table
of 5 columns (4 unused, one bytea) and one index for OID, no
compression since STORAGE EXTERNAL, ntfs tweaks (noatime
etc), ...
I'm no Windows expert, but the sysinternals tools (since bought by
Microsoft) have always proved useful to me.
Diskmon should show you what's happening on your machine:
http://technet.microsoft.com/en-us/sysinternals/bb896646.aspx
Be aware that this will generate a *lot* of data very quickly and you'll
need to spend a little time analysing it. Try it without PG running to
see what your system is up to when "idle" first to get a baseline.
Unfortunately it doesn't show disk seek times (which is probably what
you want to measure) but it should let you decode what reads/writes are
taking place when. If two consecutive disk accesses aren't adjacent then
that implies a seek of course. Worst case you get two or more processes
each accessing different parts of the disk in an interleaved arrangement.
--
Richard Huxton
Archonet Ltd
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