Date: Wed, 21 May 2014 13:05:30 -0700 From: Sean Chittenden <sean@chittenden.org> To: Matthew Seaman <matthew@FreeBSD.org> Cc: freebsd-performance@freebsd.org Subject: Re: FreeBSD 10 and PostgreSQL 9.3 scalability issues Message-ID: <sig.02185aa09c.5E8C4FB4-03A5-4460-8CA2-EF3DDBA659BB@chittenden.org> In-Reply-To: <537CEACD.8090701@FreeBSD.org> References: <5327B9B7.3050103@gmail.com> <2610F490C952470C9D15999550F67068@multiplay.co.uk> <532A192A.1070509@gmail.com> <assp.0155c70d29.23ED6415-945D-4DF5-90DD-2F2CD7E198AF@chittenden.org> <f4ead73a-fae2-4eac-8499-3cf630eb3d31@googlegroups.com> <CAJ-VmomVOWFb7X5s-amRX7QFzbmT6Kt6bB9gaPVv2_hGx1OS5g@mail.gmail.com> <572540F9-13E4-4BA9-88AE-5F47FB19450A@pingpong.net> <CAJKO3mUTwgiQenSLYfOxHrZxuPQ9kvUPC44MrbLjvpLE=toZQA@mail.gmail.com> <1BC3D447-2044-4AB8-B183-B83957BC9112@pingpong.net> <CAJKO3mX5KA8HZ5tQGTyOgfKbS6HvUvYH-gvzeewTkh3nWz=NRg@mail.gmail.com> <1473AF7C-B190-4CD4-B611-BA4090A081CB@pingpong.net> <sig.02184fa928.F0529F5B-72EC-4E68-A4BD-75276C70AC1C@chittenden.org> <537CEACD.8090701@FreeBSD.org>
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>>> I did some tests with zfs, and results where appallingly bad, but = that was with db size > ram.=20 >>>>=20 >>>> 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.=20 >> 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: >>=20 >> http://people.freebsd.org/~seanc/pg9.3-fbsd10-profiling/ >>=20 >> 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 >>=20 >=20 > 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) When the working set fits in RAM (OS + PG), there isn't a performance = difference between 9.2 and 9.3. This is a good data point. I will try and reproduce this workload and = will run the performance profiling again to see if something else pops = up in the profiling. -sc -- Sean Chittenden sean@chittenden.org
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