On 5 May 2017 at 14:04, Tom Lane <t...@sss.pgh.pa.us> wrote: > Craig Ringer <craig.rin...@2ndquadrant.com> writes: >> We're carefully maintaining this bizarre cognitive dissonance where we >> justify the need for using this as a planner hint at the same time as >> denying that we have a hint. That makes it hard to make progress here. >> I think there's fear that we're setting some kind of precedent by >> admitting what we already have. > > I think you're overstating the case. It's clear that there's a > significant subset of CTE functionality where there has to be an > optimization fence. The initial implementation basically took the > easy way out by deeming *all* CTEs to be optimization fences. Maybe > we shouldn't have documented that behavior, but we did. Now we're > arguing about how much of a compatibility break it'd be to change that > planner behavior. I don't see any particular cognitive dissonance here, > just disagreements about the extent to which backwards compatibility is > more important than better query optimization.
How about we get the ball rolling on this in v10 and pull that part out of the docs. If anything that'll buy us a bit more wiggle room to change this in v11. I've attached a proposed patch. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
doc_caution_about_cte_changes_in_the_future.patch
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