Re: determine snapshot after obtaining locks for first statement

"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> ...  The precise
> conditions in which an UPDATE or DELETE can view an inconsistent
> database state (and therefore potentially persist something based on
> that inconsistent state) are that it has a FROM clause and/or
> subqueries which reference data changed by a concurrent database
> transaction which also affects rows which are targets of the UPDATE
> or DELETE.

Are we sure that's a precise and complete description?  I don't have
a problem with putting a description just like that in the docs, but
I'm not yet convinced it's right.
        regards, tom lane