Re: Trouble with hashagg spill I/O pattern and costing

On Thu, May 28, 2020 at 06:14:55PM -0700, Jeff Davis wrote:
>On Thu, 2020-05-28 at 20:57 +0200, Tomas Vondra wrote:
>> Attached is a patch adding CP_SMALL_TLIST to create_agg_plan and
>> create_groupingsets_plan.
>
>Looks good, except one question:
>
>Why would aggstrategy ever be MIXED when in create_agg_path? Wouldn't
>that only happen in create_groupingsets_path?
>

Ah, right. Yeah, we only need to check for AGG_HASH here. Moreover,
AGG_MIXED probably does not need the tlist tweak, because the input
should be pre-sorted as with AGG_SORTED.

And we should probably do similar check in the create_groupinsets_path,
I guess. At first I thought we can't do that before inspecting rollups,
which only happens later in the function, but now I see there's
aggstrategy in GroupingSetsPath too.


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
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