On 21/05/2014 18:17, Sean Chittenden wrote: >> I did some tests with zfs, and results where appallingly bad, but that was >> with db size > ram. >> > >> > I think the model used by PostgreSQL, as most databases, are very disk >> > block centric. Using zfs makes it hard to get good performance. But this >> > was some time ago, maybe things have improved. > I have some hardware that I ran with last week wherein I was *not* able to > reproduce any performance difference between ZFS and UFS2. On both UFS2 and > ZFS I was seeing the same performance when using a a RAID10 / set of mirrors. > I talked with the Dragonfly folk who originally performed these tests and > they also saw the same thing: no real performance difference between ZFS and > UFS. I ran my tests on a host with 16 drive, 10K SAS, 192GB RAM. I also > created a kernel profiling image and ran the 20 concurrent user test under > kgprof(1), dtrace, and pmcstat and have the results available: > > http://people.freebsd.org/~seanc/pg9.3-fbsd10-profiling/ > > There are some investigations that are ongoing as a result of these findings. > The dfly methodology was observed when generating these results. Stay tuned. > -sc >
I'm not sure that the ZFS vs UFS2 question is at the core of the
performance problem. We're definitely seeing marked slowdowns between
Pg 9.2 and 9.3 on UFS2 (RAID10 + Dell H710p (mfi) raid controller with
1GB NVRAM)
In our case the DB size is significantly bigger than RAM, and we also
run with a large (3GB) work mem, which seems to exacerbate the slow-down
effect.
Cheers,
Matthew
--
Dr Matthew J Seaman MA, D.Phil.
PGP: http://www.infracaninophile.co.uk/pgpkey
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