| From: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
|---|---|
| To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | Melanie Plageman <melanieplageman(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, HeikkiLinnakangas <hlinnaka(at)iki(dot)fi> |
| Subject: | Re: Trouble with hashagg spill I/O pattern and costing |
| Date: | 2020-05-29 13:04:54 |
| Message-ID: | 20200529130454.el6qyuukj3ofs4eu@development |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
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
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
| Attachment | Content-Type | Size |
|---|---|---|
| hashagg-tlist-fix-v2.patch | text/plain | 2.1 KB |
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