From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Daniel Åkerud <zilch(at)home(dot)se> |
Cc: | "PostgreSQL-general" <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: Foreign Keys Constraints, perforamance analysis |
Date: | 2001-06-23 21:40:10 |
Message-ID: | 8795.993332410@sss.pgh.pa.us |
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Lists: | pgsql-general |
=?iso-8859-1?Q?Daniel_=C5kerud?= <zilch(at)home(dot)se> writes:
>> ... Not surprising that it's much slower. The real
>> question is what this scenario has to do with production activities.
> It has nothing to do with production activities. I just want to know how,
> and how much, Foreign Keys Constraints affect performance.
My point is that unless bulk delete is an operation you do a lot,
this measurement has little to do with everyday performance. A more
reasonable test (I think) would be to time deletion of a *single* person
record --- and the associated implicit deletion of a small number of
dependent records --- against deletion of the same person record and
explicit deletion of the same number of dependent records. That
actually has something to do with performance of real-world applications
that delete individual records. As is, you are measuring (in effect)
DELETE FROM married;
against
FOR akey IN (SELECT key FROM married) DO
DELETE FROM married WHERE key = akey;
and then blaming the speed difference on foreign keys. It's got nothing
to do with foreign keys and everything to do with number of queries
issued.
regards, tom lane
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