Richard Huxton wrote:
Heikki Linnakangas wrote:
The problem is that the new tuple version is checked only against the condition in the update rule, id=OLD.id, but not the condition in the original update-claus, dt='a'.


Yeah, that's confusing :(.

Bit more than just normal rule confusion I'd say. Try the following two statements in parallel (assuming you've just run the previous):

UPDATE test SET dt='c';
UPDATE test SET dt='x' FROM test t2 WHERE test.id=t2.id AND t2.dt='b';

This isn't a problem with the view mechanism - it's a problem with re-checking clauses involving subqueries or joins I'd guess.

I'm trying to decide if it's unexpected or just plain wrong, and I think I'd have to argue wrong.

Or perhaps I'd not argue that :-/

This is really about MVCC in read committed mode, and the "just right for simpler cases":
http://www.postgresql.org/docs/8.2/interactive/transaction-iso.html#XACT-READ-COMMITTED

Clearly there needs to be a change to the sentence: "Because of the above rule, it is possible for an updating command to see an inconsistent snapshot: it can see the effects of concurrent updating commands that affected the same rows it is trying to update"

Not true if there's a subquery/join involved.

--
  Richard Huxton
  Archonet Ltd

---------------------------(end of broadcast)---------------------------
TIP 3: Have you checked our extensive FAQ?

              http://www.postgresql.org/docs/faq

Reply via email to