On Fri, 07 Apr 2006 16:06:02 -0400 Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > > The pSeries isn't much older than our Xeon machine, and I expected > > the performance level to be exemplary out of the box.. > > I'm fairly surprised too. One thing I note from your comparison of > settings is that the default WAL sync method is different on the two > operating systems. We're very read-focussed.. there's update activity, sure, but the IO is only pushing about 500KByte/sec on average, usually much less. I also have fsync switched off - yes dangerous, but I just want to eliminate IO completely as a contributing factor. > Does AIX have anything comparable to oprofile or dtrace? I've used neither on Linux, but a quick google showed up a few articles along the lines of 'in theory it shouldn't be hard to port to AIX....' but nothing concrete. My guess is IBM sell a tool to do this. Hell, the C++ compiler is £1200... (hence our use of GCC 4.1 to compile pg) > Failing a low-level profiler, there should at least be > something comparable to strace --- you should try watching some of > the backends with strace and see what their behavior is when the > performance goes south. Lots of delaying select()s or semop()s would > be a red flag. There's truss installed which seems to do the same as strace on Linux... and here's a wildly non-scientific glance.. I watched the 'topas' output (top for AIX) , identified a PID that was doing a lot of work, then attached truss to that pid. In addition to lots of send (), recv() and lseek()s... about once a minute I saw hundreds of calls to __semop() interspersed with _select(), followed by tons of lseek() +kread()+__semop() and then I can see the kwrite() to the pg logfile 246170: kwrite(2, " L O G : d u", 8) = 8 etc. Cheers, Gavin.
