=?ISO-8859-1?Q?Sebastian_B=F6ck?= <sebastianboeck@xxxxxxxxxx> 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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