| On Mon, Oct 25, 2010 at 2:21 PM, Andrà Volpato | <andre.volpato@xxxxxxxxxxxxxxxxxxxxx> wrote: | > Hi all, | > | > We are tuning a PostgreSQL box with AIX 5.3 and got stucked in a | > very odd situation. | > When a query got ran for the second time, the system seems to | > deliver the results to slow. | > | > HereÂs some background info: | > | > AIX Box: | > PostgreSQL 8.4.4, AIX 5.3-9 64bits, SAN IBM DS3400, 8x450GB SAS 15K | > Raid-5 | > 8GB RAM, 2.3GB Shared buffers | > | > Debian Box: | > PostgreSQL 8.4.4, Debian 4.3.2 64bits, SAN IBM DS3400, 5x300GB SAS | > 15K Raid-0 | > 7GB RAM, 2.1GB Shared buffers | > | > Right now, we changed lots of AIX tunables to increase disk and SO | > performance. | > Of course, postgres got tunned as well. I can post all changes made | > until now if needed. | > | > To keep it simple, I will try to explain only the buffer read issue. | > This query [1] took like 14s to run at AIX, and almost the same time | > at Debian. | > The issue is when I run it for the second time: | > AIX - 8s | > Debian - 0.3s | > | > These times keep repeating after the second run, and I can ensure | > AIX isnÂt touching the disks anymore. | > IÂve never seen this behaviour before. I heard about Direct I/O and | > I was thinking about givng it a shot. | > Any ideas? | > | | I doubt disk/io is the problem. Me either. Like I said, AIX do not touch the storage when runing the query. It became CPU-bound after data got into cache. | *) Are the plans *exactly* the same? The plan I sent refers to the AIX box: http://explain.depesz.com/s/5oz At Debian, the plan looks pretty much the same. | *) Are you running explain analyze? There are some platform specific | interactions caused by timing. Yes. IÂm not concerned about timing because the difference (8s against 0.3s) is huge. | *) Are you transferring the data across the network? rule out | (horribly difficult to diagnose/fix) network effects. Not likely... Both boxes are in the same Bladecenter, using the same storage. | | merlin []Âs, Andre Volpato -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
