Horton

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

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Melanie Plageman <melanieplageman@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, HeikkiLinnakangas <hlinnaka@iki.fi>
Date: 2020-05-29T20:12:40Z
Lists: pgsql-hackers 
On Fri, 2020-05-29 at 15:04 +0200, Tomas Vondra wrote:
> 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.

Looks good.

	Jeff

Commits

  1. Use CP_SMALL_TLIST for hash aggregate

  2. Avoid fragmentation of logical tapes when writing concurrently.