On 06/28/2018 06:52 PM, Teodor Sigaev wrote:
I'm afraid that's a misunderstanding - my objections did not really go
away. I'm just saying my claim that we're not messing with order of
grouping keys is not entirely accurate, because we do that in one
particular case.
I still think we need to be careful when introducing new optimizations
in this area - reordering the grouping keys by ndistinct, ORDER BY or
whatever. In particular I don't think we should commit these patches
that may quite easily cause regressions, and then hope some hypothetical
future patch fixes the costing. Those objections still stand.
Pls, have a look at https://commitfest.postgresql.org/18/1706/
I tried to attack the cost_sort() issues and hope on that basis we can
solve problems with 0002 patch and improve incremental sort patch.
OK, will do. Thanks for working on this!
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
