From: | Jamie Koceniak <jkoceniak(at)mediamath(dot)com> |
---|---|
To: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
Cc: | "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: Recursive query performance issue |
Date: | 2015-10-21 17:55:14 |
Message-ID: | BY2PR12MB07116999B34B8D48E00C1FBEA4380@BY2PR12MB0711.namprd12.prod.outlook.com |
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Lists: | pgsql-performance |
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)
Thanks,
Jamie
From: Pavel Stehule [mailto:pavel(dot)stehule(at)gmail(dot)com]
Sent: Wednesday, October 21, 2015 12:04 AM
To: Jamie Koceniak
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: [PERFORM] Recursive query performance issue
Hi
2015-10-20 19:34 GMT+02:00 Jamie Koceniak <jkoceniak(at)mediamath(dot)com<mailto:jkoceniak(at)mediamath(dot)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
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