Re: SSI predicate locking on heap -- tuple or row?

Aidan Van Dyk <aidan(at)highrise(dot)ca> writes:
> So, if SSI conflicts something on the UPDATE case, it would necessrily
> have to conflict the DELETE+INSERT case as well, and vice-versa.

This argument is fundamentally bogus, because an UPDATE is not the same
thing as DELETE followed by INSERT. In the former case the new tuple
will have a ctid link from the old one; in the latter case not. And
that will affect the behavior of subsequent operations. Another
user-visible difference is that if the table has OIDs, the latter case
will (usually) give the new tuple a different OID. Or if you don't like
OIDs, think about a serial column. Or an ON INSERT trigger with
side-effects.

It may be that the result Kevin seeks to prove is in fact true, but an
argument that requires the assumption that UPDATE is indistinguishable
from DELETE+INSERT isn't going to persuade me, because I don't have any
trouble whatsoever in distinguishing them.

regards, tom lane