Re: 9.5 alpha: some small comments on BRIN and btree_gin

On 07/07/2015 06:28 AM, Marc Mamin wrote:
> Sure, but on the other hand, they are so small and quick to build 
> that they seem to be a good alternative when other index types are too costly, 
> even if theses indexes can't deal well with all data ranges passed as query condition.
> 
> Hence it would be fine if the planner could reject these indexes in the bad cases.

Oh, sorry!  I didn't realize that the planner was using the BRIN index
even when it was useless; your email wasn't clear.

The problem here is that the usefulness of BRIN indexes as a cost
calculation should take correlation into account, heavily.  Can we do
that?  Is correlation even part of the index costing method now?  How
accurate are our correlation estimates?

-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com