| From: | "Tomas Vondra" <tv(at)fuzzy(dot)cz> |
|---|---|
| To: | "Andy Colson" <andy(at)squeakycode(dot)net> |
| Cc: | "Craig Ringer" <ringerc(at)ringerc(dot)id(dot)au>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: IN or EXISTS |
| Date: | 2011-08-31 14:19:36 |
| Message-ID: | cf12201c9c3aa4a29a5c2ed26c7853ce.squirrel@sq.gransy.com |
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| Lists: | pgsql-performance |
On 31 Srpen 2011, 15:59, Andy Colson wrote:
> I assume:
> Buckets: 16384 Batches: 1 Memory Usage: 4531kB
>
> That means a total of 4.5 meg of ram was used for the hash, so if my
> work_mem was lower than that it would swap? (or choose a different plan?)
Why don't you try that? Just set the work_mem to 1MB or so and run the query.
I think it'll use the same plan but multiple batches - read just part of
the inner table so that the hash table fits into work_mem, scan the outer
table etc. The downside is it'd rescan the outer table several times.
Tomas
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