From: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance-owner@postgresql.org] On Behalf Of Dave Johansen Sent: Wednesday, October 15, 2014 4:05 PM To: Josh Berkus Cc: pgsql-performance Subject: Re: [PERFORM] Partitions and work_mem?
On Wed, Oct 15, 2014 at 10:10 AM, Josh Berkus <josh@agliodbs.com> wrote:
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.
Thanks for the feedback. That's very helpful.
BTW, 8.4 is EOL. Maybe time to upgrade?
RHEL 6 isn't EOLed and we're working on moving to RHEL 7 but it's a slow process that will probably take quite a bit of time, if it ever happens.