From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: JIT compiling with LLVM v11 |
Date: | 2018-03-06 21:20:25 |
Message-ID: | 18415.1520371225@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Andres Freund <andres(at)anarazel(dot)de> writes:
> I'm not too worried about that scenario. If, for a cheap plan, the
> planner ends up with a seqscan despite it being disabled, you're pretty
> close to randomly choosing plans already, as the pruning doesn't work
> well anymore (as the %1 percent fuzz factor in
> compare_path_costs_fuzzily() swamps the actual plan costs).
Something I've wanted to do for awhile is to get rid of disable_cost
in favor of pruning disabled plans through logic rather than costing.
I've looked at this once or twice, and it seems doable but not entirely
trivial --- the sticky bits are places where you do need to allow a
disabled plan type because there's no other alternative. But if we
could get that done, it'd help with this sort of problem.
regards, tom lane
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