From: Marc G. Fournier <scrappy@hub.org>
To: pgsql-sql@postgresql.org
Subject: How do FKs work?
Date: Sat, 9 Oct 2004 15:08:51 -0300 (ADT)
Message-ID: <20041009145332.D54093@ganymede.hub.org> (raw)
Got a problem here, and this is a new area for me ... analyzing FKs and
improving their performance :)
Have a table with two FKs on it ... 2 different fields in the table point
to the same field in another table ...
When I do an 'EXPLAIN ANALYZE DELETE FROM table WHERE field = #;', it
never comes back ... or, at lesat, takes a *very* long time ...
If I do a count(1) for that #, there are 1639 rows ...
Now, 'ON DELETE' is set to 'NO ACTION', so my *guess* is that all it does
is a 'SELECT FROM table WHERE field = value' on the referenced table, to
make sure it exists ...
Is this correct? So, its effectively having to do 3278 "SELECTS" against
the REFERENCED table? (two fields have contraints on them, 1639 rows to be
deleted) ... ?
----
Marc G. Fournier Hub.Org Networking Services (http://www.hub.org)
Email: scrappy@hub.org Yahoo!: yscrappy ICQ: 7615664
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To: pgsql-sql@postgresql.org
Cc: scrappy@hub.org
Subject: Re: How do FKs work?
In-Reply-To: <20041009145332.D54093@ganymede.hub.org>
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