On 13 September 2010 17:27, Stefan Kaltenbrunner <ste...@kaltenbrunner.cc> wrote: > On 09/13/2010 06:05 PM, Greg Smith wrote: >> >> Domas Mituzas wrote: >>> >>> I've been playing around today a lot with sysbench, and observed that >>> 2.6.32 kernel supplied by Ubuntu is having perf regression with PG >>> (which does not affect MySQL), compared to 2.6.28 builds I have. >>> What I observed can be seen in a paste at >>> http://p.defau.lt/?8_GQV82Pz3_SDZbNOdP93Q (db12 is 2.6.28, db20 is >>> 2.6.32 - 2.6.32-24-server). >>> Machines are two socket quad-opterons 2356s. >>> oprofile output can be seen at >>> http://p.defau.lt/?OIR1vDFK4cze_fmBTQbV9w - system has >20% of idle >>> cpu, which is somewhere in the top symbol :) >> >> Are you using the same filesystem setup on both setups? And regardless, >> what is that filesystem? We know that between 2.6.28 and 2.6.32 the >> kernel improved how it handles fsync requests in a good way from a >> reliability perspective (to fix bugs that could cause data loss before), >> particularly on ext4, so it's possible the regression you're seeing is >> just the expense of handling things properly. >> >> If you already have sysbench on there, I'd suggest comparing the two >> systems by seeing how fast each can execute fsync requests: >> >> sysbench --test=fileio --file-fsync-freq=1 --file-num=1 >> --file-total-size=16384 --file-test-mode=rndwr run | grep "Requests/sec" >> >> To help distinguish whether this regression might be coming from the >> already known changes in that area, or if it's instead from something >> that's impacting CPU efficiency. >> >> Also, it's easy to see a performance change of this size just from the >> database files being on a different part of the disk if you didn't >> control for that. Disks are almost twice as fast at their beginning than >> their end nowadays. > > well the main point here is that domas is doing a pure read-only test on a > rather small workload so it should entirely fit in memory... > From some very quick testing here as well it rathers seems that for some > reason the CPU scheduler is not actually scheduling us all the available CPU > on 2.6.32 or we are having some sort of locking issue that is more exposed > on this kernel.
I thought sysbench was designed for MySQL benchmarks. How new is the PostgreSQL driver? Is it stable yet? -- Thom Brown Twitter: @darkixion IRC (freenode): dark_ixion Registered Linux user: #516935 -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
