| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | David Link <dlink(at)soundscan(dot)com> |
| Cc: | pgsql-general(at)postgresql(dot)org |
| Subject: | Re: EXPLAIN SELECT .. does not return |
| Date: | 2006-03-30 03:10:46 |
| Message-ID: | 9146.1143688246@sss.pgh.pa.us |
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| Lists: | pgsql-general |
David Link <dlink(at)soundscan(dot)com> writes:
> The following large EXPLAIN SELECT Statement fails to return, but
> continues to take up processing time until it is killed.
> [ 52-way join... ]
Am I right in guessing that all the sales_xxx tables are the same size
and have similar statistics? I think the problem is that the planner is
faced with a large set of essentially equivalent plans and isn't pruning
the list aggressively enough. That's something we fixed in 8.0.
> Postgresql 7.4.8
You really oughta try something newer. On my machine, 7.4.12 plans a
52-way join in about a minute, and 8.0 and 8.1 in under a second.
I wonder also if there's not a better way to design the query...
maybe a UNION ALL would work better than nested joins.
regards, tom lane
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