Hi Paul, I was passed your message... regarding DSS workload with Postgres on Solaris. (I am not in the alias).
Performance is relative to your workload. Can you actually send us what you are doing in your queries, updates etc? I have been running few tests myself and here are my rules of thumbs, your mileage can vary.. http://blogs.sun.com/roller/page/jkshah?entry=tuning_postgresql_8_0_2 * Increasing checkpoint certainly helps. (I went as far as actually going to increase LOGFILE size from 16MB to 256MB and recompiling it and then using lower number of checkpoints (appropriately).. (file rotations also decreases performance) * Moving pg_xlog to a different file system and mounting that file system with "forcedirectio" also helps a lot (This increases the througput by another 2x to 5x or more.) (This can be done either by adding forcedirectio in your /etc/vfstab mount options or for existing mounts as follows: mount -o remount,forcedirectio /filesystem (Note: Database files should not be using forcedirectio otherwise file system cache will not be used for it) * I actually reduced the PG Bufferpool to 1G or less since it seemed to decrease performance as I increased its bufferpool size (depending on your workload) * If you are using SPARC then following etc commands will help.. set segmap_percent=60 set ufs:freebehind=0 This will allocate 60% of RAM for file system buffer (database files) and also cache all files (since PostgreSQL files are 1G by default) This will help your repeat queries significantly. Other things depends on what you queries you are running? If you send me few samples, I can send you appropriate DTrace scripts (Solaris 10 or higher) to run to figure out what's happening Regards, Jignesh ____________________________________________________ Jignesh K. Shah MTS Software Engineer Sun Microsystems, Inc MDE-Horizontal Technologies Email: [EMAIL PROTECTED] Phone: (781) 442 3052 http://blogs.sun.com/jkshah ____________________________________________________ ----- Original Message ----- >From Paul Johnson <[EMAIL PROTECTED]> Date Thu, 11 Aug 2005 13:23:21 +0100 (BST) To pgsql-performance@postgresql.org Subject [PERFORM] PG8 Tuning Hi all, we're running PG8 on a Sun V250 with 8GB RAM and 2*1.3GHz SPARC CPUs running Solaris 10. The DB cluster is on an external fibre-attached Sun T3 array that has 9*36GB drives configured as a single RAID5 LUN. The system is for the sole use of a couple of data warehouse developers, hence we are keen to use 'aggressive' tuning options to maximise performance. So far we have made the following changes and measured the impact on our test suite: 1) Increase checkpoint_segments from 3 to 64. This made a 10x improvement in some cases. 2) Increase work_mem from 1,024 to 524,288. 3) Increase shared_buffers from 1,000 to 262,143 (2 GB). This required setting SHMMAX=4294967295 (4 GB) in /etc/system and re-booting the box. Question - can Postgres only use 2GB RAM, given that shared_buffers can only be set as high as 262,143 (8K pages)? So far so good... 4) Move /pg_xlog to an internal disk within the V250. This has had a severe *negative* impact on performance. Copy job has gone from 2 mins to 12 mins, simple SQL job gone from 1 min to 7 mins. Not even run long SQL jobs. I'm guessing that this is because pg_xlog has gone from a 9 spindle LUN to a single spindle disk? In cases such as this, where an external storage array with a hardware RAID controller is used, the normal advice to separate the data from the pg_xlog seems to come unstuck, or are we missing something? Cheers, Paul Johnson.
--- Begin Message ---Hi all, we're running PG8 on a Sun V250 with 8GB RAM and 2*1.3GHz SPARC CPUs running Solaris 10. The DB cluster is on an external fibre-attached Sun T3 array that has 9*36GB drives configured as a single RAID5 LUN. The system is for the sole use of a couple of data warehouse developers, hence we are keen to use 'aggressive' tuning options to maximise performance. So far we have made the following changes and measured the impact on our test suite: 1) Increase checkpoint_segments from 3 to 64. This made a 10x improvement in some cases. 2) Increase work_mem from 1,024 to 524,288. 3) Increase shared_buffers from 1,000 to 262,143 (2 GB). This required setting SHMMAX=4294967295 (4 GB) in /etc/system and re-booting the box. Question - can Postgres only use 2GB RAM, given that shared_buffers can only be set as high as 262,143 (8K pages)? So far so good... 4) Move /pg_xlog to an internal disk within the V250. This has had a severe *negative* impact on performance. Copy job has gone from 2 mins to 12 mins, simple SQL job gone from 1 min to 7 mins. Not even run long SQL jobs. I'm guessing that this is because pg_xlog has gone from a 9 spindle LUN to a single spindle disk? In cases such as this, where an external storage array with a hardware RAID controller is used, the normal advice to separate the data from the pg_xlog seems to come unstuck, or are we missing something? Cheers, Paul Johnson. ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
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