From: | tv(at)fuzzy(dot)cz |
---|---|
To: | "Merlin Moncure" <mmoncure(at)gmail(dot)com> |
Cc: | tv(at)fuzzy(dot)cz, "Davenport, Julie" <jdavenport(at)ctcd(dot)edu>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: query taking much longer since Postgres 8.4 upgrade |
Date: | 2011-03-21 17:04:03 |
Message-ID: | edf1c0575ccbdb74bb93b2975acf10e6.squirrel@sq.gransy.com |
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Thread: | |
Lists: | pgsql-general |
> On Mon, Mar 21, 2011 at 11:32 AM, <tv(at)fuzzy(dot)cz> wrote:
>>> Incredible! Setting enable_nestloop off temporarily for the run of
>>> this
>>> script made it run in less than a minute (had been running in 10 or 11
>>> minutes). I think you have found a solution for many of my slow
>>> running
>>> scripts that use these same type of joins. Thanks again.
>>> Julie
>>
>> Nice. Can you post EXPLAIN ANALYZE again, so that we can see why this
>> plan
>> was evaluated as as more expensive before disabling nested loops?
>
> well the problem is obvious -- the planner is estimating ~ 250 loops,
> when it in fact has to do ~ 60k. That's a two orders of magnitude
> miss.
Yeah, you're right, although I think the estimate is 1 loop vs. 2882 loops
in reality. The 250 vs. 60k is related to the result set.
Tomas
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