On 09/12/2011 12:47 PM, Andy Colson wrote:
work_mem is not the total a query can use. I believe each step can use that much, and each backend can use it for multiple bits. So if you had two backends, each doing 2 sorts, you'd use 2*2 = 4 * 2GB = 8GB.
Exactly. Find a big query somewhere in your system. Use EXPLAIN to examine it. Chances are, that one query has one or more sorts. Each one of those gets its own work_mem. Each sort. The query have four sorts? It may use 4*work_mem. On a whim a while back, I doubled our 8MB setting to 16MB on a test system. During a load test, the machine ran out of memory, swapped out, and finally crashed after the OOM killer went nuts.
Set this value *at your own risk* and only after *significant* testing. Having it too high can have rather unexpected consequences. Setting it to 1 or 2GB, unless you have VERY few threads, or a TON of memory, is a very, very bad idea.
-- Shaun Thomas OptionsHouse | 141 W. Jackson Blvd. | Suite 800 | Chicago IL, 60604 312-676-8870 sthomas@xxxxxxxxx ______________________________________________ See http://www.peak6.com/email-disclaimer/ for terms and conditions related to this email -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
