Re: 9.5: Memory-bounded HashAgg

Summary of this thread so far:

There was a lot of discussion comparing this with Tomas Vondra's Hash 
Join patch. The conclusion was that while it would be nice to be able to 
dump transition state to disk, for aggregates like array_agg, the patch 
is fine as it is. Dumping transition states would require much more 
work, and this is already useful without it. Moreover, solving the 
array_agg problem later won't require a rewrite; rather, it'll build on 
top of this.

You listed a number of open items in the original post, and these are 
still outstanding:

> * costing
> * EXPLAIN details for disk usage
> * choose number of partitions intelligently
> * performance testing

I think this is enough for this commitfest - we have consensus on the 
design. For the next one, please address those open items, and resubmit.

- Heikki