| From: | Josh Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | Dave Johansen <davejohansen(at)gmail(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Partitions and work_mem? |
| Date: | 2014-10-15 17:10:58 |
| Message-ID: | 543EAAA2.8010701@agliodbs.com |
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| Lists: | pgsql-performance |
On 10/14/2014 10:08 AM, Dave Johansen wrote:
> I'm running Postgres 8.4 on RHEL 6 64-bit and I had a question about how
> work_mem and partitions interact.
>
> https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server#work_mem
> The above wiki states that "if a query involves doing merge sorts of 8
> tables, that requires 8 times work_mem." If I have a table that is
> partitioned does each partition count as a "table" and get its on work_mem?
In theory, this could happen. In practice, based on tests I did at Sun
with DBT3 and 8.3, no backend ever used more than 3X work_mem. This is
partly because the level of parallelism in postgres is extremely
limited, so we can't actually sort 8 partitions at the same time.
BTW, 8.4 is EOL. Maybe time to upgrade?
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com
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