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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