Re: "explain analyse" much slower than actual query

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Phil Endecott" <spam_from_postgresql_general(at)chezphil(dot)org>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: "explain analyse" much slower than actual query
Date: 2007-01-28 21:28:15
Message-ID: 22445.1170019695@sss.pgh.pa.us
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"Phil Endecott" <spam_from_postgresql_general(at)chezphil(dot)org> writes:
> If I understand it correctly, it is still doing a sequential scan on
> part_tsearch that does not terminate early due to the limit clause. So
> I'm still seeing run times that are rather worse than I think should be
> possible. Can it not step through the indexes in the way that it does
> for a Merge Join until it has got enough results to satisfy the limit,
> and then terminate?

Nope, there is not that much intelligence about NOT IN.

You could possibly manually rewrite the thing as a LEFT JOIN
with a WHERE inner-join-key IS NULL clause. This would probably
lose if most of the outer relation's rows join to many inner rows,
though.

regards, tom lane

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