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
855-TREBLE2 (855-873-2532)   mobile: 512-569-9461

Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:

Reply via email to