Tom Lane wrote:
=?ISO-8859-1?Q?Sebastian_B=F6ck?= <[EMAIL PROTECTED]> writes:
Why does Postgres perform updates to tables, even if the row doesn't
change at all?
Because testing for this would almost surely be a net loss for the vast
majority of applications. Checking to see if the new row value exactly
equals the old is hardly a zero-cost operation; if you pay that on every
update, that's a lot of overhead that you are hoping to make back by
sometimes avoiding the physical store of the new tuple. In most
applications I think the "sometimes" isn't going to be often enough
to justify doing it.
If you have a particular table in a particular app where it is worth it,
I'd recommend writing a BEFORE UPDATE trigger to make the comparisons
and suppress the update when NEW and OLD are equal.
In any case, what if I have a trigger that's supposed to increment a
counter or similar if issue a supposedly "unneeded" update.
--
Richard Huxton
Archonet Ltd
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