Re: Final Patch for GROUPING SETS

On Thu, May 14, 2015 at 07:50:31AM +0200, Andres Freund wrote:
> I still believe that the general approach of chaining vs. a union or CTE
> is correct due to the efficiency arguments upthread.  My problem is
> that, unless I very much misunderstand something, the current
> implementation can end up requiring roughly #sets * #input of additional
> space for the "sidechannel tuplestore" in some bad cases.  That happens
> if you group by a couple clauses that each lead to a high number of
> groups.

Correct.

> Andrew, is that a structure you could live with, or not?
> 
> Others, what do you think?

Andrew and I discussed that very structure upthread:

http://www.postgresql.org/message-id/20141231085845.GA2148306@tornado.leadboat.com
http://www.postgresql.org/message-id/87d26zd9k8.fsf@news-spur.riddles.org.uk
http://www.postgresql.org/message-id/20141231210553.GB2159277@tornado.leadboat.com

I still believe the words I wrote in my two messages cited.