On 11/21/2012 09:35 AM, Craig James wrote: > Why not make an explicit hint syntax and document it? I've still don't > understand why "hint" is a dirty word in Postgres. There are a > half-dozen or so ways in common use to circumvent or correct > sub-optimal plans. > The reason usually given is that hints provide easy workarounds for planner and stats issues, so people don't report problems or fix the underlying problem. Of course, if that's all there was to it, `OFFSET 0` would be made into an error or warning, or ignored and not fenced. The reality is, as you say, that there's a need, because the planner can never be perfect - or rather, if it were nearly perfect, it'd take so long to read the stats and calculate plans that everything would be glacially slow anyway. The planner has to compromise, and so cases will always arise where it needs a little help. I think it's time to admit that and get the syntax in place for CTEs so there's room to optimize them later, rather than cementing CTEs-as-fences in forever as a Pg quirk. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
