On Mon, Sep 13, 2010 at 12:05 PM, Greg Smith <g...@2ndquadrant.com> 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.
Greg, have you run into any other evidence suggesting a problem with 2.6.32? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
