Re: DELETE, INSERT vs SELECT, UPDATE || INSERT

Anton Maksimenkov <engineer(at)hlebprom(dot)ru> writes:
> Second idea was to try to SELECT (user, cookie) pair and then UPDATE
> it if it exists or INSERT if not. I has thought that if UPDATE will
> rewrite same place in file with new count it may lead to more compact
> table (file not grow and information about actual rows in file will
> not changed).

You're wasting your time, because Postgres doesn't work that way.
UPDATE is really indistinguishable from DELETE+INSERT, and there will
always be a dead row afterwards, because under MVCC rules both versions
of the row have to be left in the table for some time after your
transaction commits. See
http://www.postgresql.org/docs/8.1/static/mvcc.html

regards, tom lane