On Tue, Nov 20, 2012 at 4:22 PM, Merlin Moncure <mmoncure@xxxxxxxxx> wrote: > On Wed, Nov 14, 2012 at 8:03 PM, Peter Geoghegan <peter@xxxxxxxxxxxxxxx> wrote: >> On 15 November 2012 01:46, Andrew Dunstan <andrew@xxxxxxxxxxxx> wrote: >>> It cuts both ways. I have used CTEs a LOT precisely because this behaviour >>> lets me get better plans. Without that I'll be back to using the "offset 0" >>> hack. >> >> Is the "OFFSET 0" hack really so bad? We've been telling people to do >> that for years, so it's already something that we've effectively >> committed to. > > IMSNHO, 'OFFSET 0' is completely unreadable black magic. I agree with > Andrew: CTEs allow for manual composition of queries and can be the > best tool when the planner is outsmarting itself. In the old days, > we'd extract data to a temp table and join against that: CTE are > essentially a formalization of that technique. I like things the way > they are; if CTE are hurting your plan, that's an indication you're > using them inappropriately. I agree, **BUT**, I cannot imagine how pushing constraints to the CTE (under adequate conditions) could be anything but beneficial. It *could* just be a lack of imagination on my part. But if it were not, then it'd be nice for it to be done automatically (since this particular CTE behavior bites enough people already). -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
