From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | "Eric B(dot) Ridge" <ebr(at)tcdi(dot)com> |
Cc: | Postgresql <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: Query plans for plpgsql triggers |
Date: | 2006-03-25 04:39:40 |
Message-ID: | 14507.1143261580@sss.pgh.pa.us |
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Lists: | pgsql-general |
"Eric B. Ridge" <ebr(at)tcdi(dot)com> writes:
> When is the UPDATE statement inside foo() planned? When the trigger
> is first created, or when it's first used per backend, or every time
> it's used per backend?
First use per backend, ignoring corner cases such as replacing the
function definition.
> I dunno what plan is being generated, but it's gotta be using a
> sequential scan.
The issue is probably that the planner is seeing a parameterized
query. Try this:
prepare foo(int8) as update some_other_table SET field = 'value' WHERE id = $1;
explain execute foo(42);
and see what plan you get. If the id field has sufficiently
discouraging statistics then the planner may think that a seqscan
is the safest plan. In a "normal" query where you're comparing id
to a constant, the planner can see whether the constant matches any
of the most common values for the column --- if it doesn't then an
indexscan is a good plan.
If you really want a replan every time, you can get it by using
EXECUTE.
regards, tom lane
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