>>>>> "Tom" == Tom Lane <t...@sss.pgh.pa.us> writes:
Tom> I was interested to find, while writing the docs, that it's a real Tom> struggle to invent plausible reasons to write MATERIALIZED given Tom> the above specification. You pretty much have to have lied to the Tom> planner, eg by making a volatile function that's not marked Tom> volatile, before there's a real need for that. Am I missing Tom> something? If I'm not, then we're in a really good place Tom> backwards-compatibility-wise, because the new default behavior Tom> shouldn't break any cases where people weren't cheating. The cases where the new default will break things are where people used WITH to force a choice of join order or otherwise constrain the planner in order to avoid a misplan. I'm not sure we should nail down the rule that the absence of NOT MATERIALIZED will mean a multiply-referenced CTE is evaluated once. One would hope that in the future the planner might be taught to inline or not in that case depending on cost. I think it makes more sense to say that we never inline if MATERIALIZED is specified, that we always inline if NOT MATERIALIZED is specified, and that if neither is specified the planner will choose (but perhaps note that currently it always chooses only based on refcount). -- Andrew (irc:RhodiumToad)
