On 9/8/16 11:35 PM, Tom Lane wrote:
This isn't simple because there are often *lots* of variants. You
> don't just want to see the "top 10" candidate plans, because they're
> probably a bunch of small variants on the same plan; the ones you'll
> be interested in will probably be very different plans with very bad
> relative estimates.
The other big problem here is that the planner tries *very* hard to reject
losing paths early; so it does not even form an explainable plan for a
large fraction of the search space. (And if it did, you'd be dead before
you got your EXPLAIN result back.)
What I've wished for is the ability to see plans that were close in cost
to the best case scenario, since that indicates that a slight change in
statistics would push the planner in another direction (sometimes with
disastrous results). Maybe allowing some number of plans to bubble up if
they were within X percent of the winner wouldn't be that horrible.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
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