On Wed, Nov 2, 2011 at 12:13 PM, Robert Haas <robertmhaas@xxxxxxxxx> wrote: > I wonder if we need to rethink, though. We've gotten a number of > reports of problems that were caused by single-use CTEs not being > equivalent - in terms of performance - to a non-CTE formulation of the > same idea. It seems necessary for CTEs to behave this way when the > subquery modifies data, and there are certainly situations where it > could be desirable otherwise, but I'm starting to think that we > shouldn't do it that way by default. Perhaps we could let people say > something like WITH x AS FENCE (...) when they want the fencing > behavior, and otherwise assume they don't (but give it to them anyway > if there's a data-modifying operation in there). Well, in my case, I got performance thanks to CTEs *being* optimization fences, letting me fiddle with query execution. And I mean, going from half-hour queries to 1-minute queries. It is certainly desirable to maintain the possibility to use fences when needed. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
