On Mon, Oct 25, 2010 at 2:21 PM, André 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. > > Here´s 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 isn´t touching the disks anymore. > I´ve 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. *) Are the plans *exactly* the same? *) Are you running explain analyze? There are some platform specific interactions caused by timing. *) Are you transferring the data across the network? rule out (horribly difficult to diagnose/fix) network effects. merlin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
