On Tue, Mar 13, 2012 at 3:48 PM, Robert Haas <robertmh...@gmail.com> wrote: > On Mon, Mar 12, 2012 at 4:45 PM, Jeff Janes <jeff.ja...@gmail.com> wrote: >> Rerunning all 4 benchmarks (both 16MB and 32MB wal_buffers on both >> machines) with fsync=off (as well as synchronous_commit=off still) >> might help clarify things. > > I reran the 32-client benchmark on the IBM machine with fsync=off and got > this: > > 32MB: tps = 26809.442903 (including connections establishing) > 16MB: tps = 26651.320145 (including connections establishing) > > That's a speedup of nearly a factor of two, so clearly fsync-related > stalls are a big problem here, even with wal_buffers cranked up > through the ceiling.
And here's a tps plot with wal_buffers = 16MB, fsync = off. The performance still bounces up and down, so there's obviously some other factor contributing to latency spikes, but equally clearly, needing to wait for fsyncs makes it a lot worse. I bet if we could understand why that happens, we could improve things here a good deal. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
<<attachment: tps-16MB.no-fsync.png>>
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