David Rowley <dgrowle...@gmail.com> writes: > It looks like the existing join removals are done quite early in the > planning and redundant joins are removed before any subqueries from that > query are planned. So this innerrel->subroot->parse has not been done yet. > It seems to be done later in query_planner() when make_one_rel() is called.
It's true that we don't plan the subquery till later, but I don't see why that's important here. Everything you want to know is available from the subquery parsetree; so just look at the RTE, don't worry about how much of the RelOptInfo has been filled in. > The best I can come up with on how to implement this is to have 2 stages of > join removals. Stage 1 would be the existing stage that attempts to remove > joins from non subqueries. Stage 2 would happen just after make_one_rel() > is called from query_planner(), this would be to attempt to remove any > subqueries that are not need, and if it managed to remove any it would > force a 2nd call to make_one_rel(). That sounds like a seriously bad idea. For one thing, it blows the opportunity to not plan the subquery in the first place. For another, most of these steps happen in a carefully chosen order because there are interdependencies. You can't just go back and re-run some earlier processing step. A large fraction of the complexity of analyzejoins.c right now arises from the fact that it has to undo some earlier processing; that would get enormously worse if you delayed it further. BTW, just taking one step back ... this seems like a pretty specialized requirement. Are you sure it wouldn't be easier to fix your app to not generate such silly queries? regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers