Re: SSD + RAID

Richard Neill wrote:
> The key issue for short,fast transactions seems to be
> how fast an fdatasync() call can run, forcing the commit to disk, and
> allowing the transaction to return to userspace.
> Attached is a short C program which may be of use.
Right. I call this the "commit rate" of the storage, and on traditional
spinning disks it's slightly below the rotation speed of the media (i.e.
7200RPM = 120 commits/second). If you've got a battery-backed cache
in front of standard disks, you can easily clear 10K commits/second.

I normally test that out with sysbench, because I use that for some
other tests anyway:

sysbench --test=fileio --file-fsync-freq=1 --file-num=1
--file-total-size=16384 --file-test-mode=rndwr run | grep "Requests/sec"

--
Greg Smith 2ndQuadrant Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.com