| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Pavel Velikhov <pvelikhov(at)yahoo(dot)com> |
| Cc: | "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: need help with a query |
| Date: | 2007-10-19 16:34:01 |
| Message-ID: | 12689.1192811641@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Pavel Velikhov <pvelikhov(at)yahoo(dot)com> writes:
> Got a very different query plan this time, with a hash join between links and articles. At least now postgres is using both shared memory buffers and working mem, but its still completely IO bound, only getting in 5-6% CPU once in a while. I guess I can't squeeze more out of the laptop, but I also have a machine with 16GB RAM that I'll try this on next. Should I allocate tons of memory into shared buffers or into the working memory?
For a hash join, I think you want to raise work_mem as high as you can
(without driving the system into swapping). It won't read any block of
the tables more than once, so there's no point in having lots of
buffers.
regards, tom lane
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