adama_prod=# SHOW shared_buffers; shared_buffers ---------------- 64GB From: Pavel Stehule [mailto:pavel.steh...@gmail.com] Sent: Wednesday, October 21, 2015 12:26 PM To: Jamie Koceniak Cc: pgsql-performance@postgresql.org Subject: Re: [PERFORM] Recursive query performance issue
2015-10-21 20:51 GMT+02:00 Jamie Koceniak <jkocen...@mediamath.com<mailto:jkocen...@mediamath.com>>: Hi Pavel, Or were you referring to SHMMAX? value of shared_buffers - run SQL statements SHOW shared_buffers; Regards Pavel Thanks From: Jamie Koceniak Sent: Wednesday, October 21, 2015 11:40 AM To: 'Pavel Stehule' Cc: pgsql-performance@postgresql.org<mailto:pgsql-performance@postgresql.org> Subject: RE: [PERFORM] Recursive query performance issue Ok df -h /dev/shm Filesystem Size Used Avail Use% Mounted on tmpfs 406G 0 406G 0% /run/shm Ok I will try lowering it. From: Pavel Stehule [mailto:pavel.steh...@gmail.com] Sent: Wednesday, October 21, 2015 11:24 AM To: Jamie Koceniak Cc: pgsql-performance@postgresql.org<mailto:pgsql-performance@postgresql.org> Subject: Re: [PERFORM] Recursive query performance issue 2015-10-21 19:55 GMT+02:00 Jamie Koceniak <jkocen...@mediamath.com<mailto:jkocen...@mediamath.com>>: Hi Pavel, Thanks for the reply. 1. The queries aren’t waiting on any locks. The query has a recursive join that uses a table with only 80k records and that table is not updated often. 2. The I/O load was not high. CPU utilization was very high and load was very high. We have a large effective_cache_size = 512GB (25% of total memory) so your server has 2TB RAM? It is not usual server - so this issue can be pretty strange :( What is size of shared memory? Probably is significantly lower than effective_cache_size? Try to reduce effective cache size to be lower than shared buffers Regards Pavel Thanks, Jamie From: Pavel Stehule [mailto:pavel.steh...@gmail.com<mailto:pavel.steh...@gmail.com>] Sent: Wednesday, October 21, 2015 12:04 AM To: Jamie Koceniak Cc: pgsql-performance@postgresql.org<mailto:pgsql-performance@postgresql.org> Subject: Re: [PERFORM] Recursive query performance issue Hi 2015-10-20 19:34 GMT+02:00 Jamie Koceniak <jkocen...@mediamath.com<mailto:jkocen...@mediamath.com>>: Version: ----------------------------------------------------------------------------------------------- PostgreSQL 9.1.14 on x86_64-unknown-linux-gnu, compiled by gcc (Debian 4.7.2-5) 4.7.2, 64-bit Query Plan http://explain.depesz.com/s/4s37 Normally, this query takes around 200-300 ms to execute. However when several queries are run concurrently, query performance drops to 30-60 seconds. there can be few reasons: 1. locking - are you sure, so your queries don't wait on locks? 2. issues with cache stability - is there high IO load? You can try to increase effective_cache_size (or decrease if you have not enough memory) Regards Pavel
