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>, Melanie Plageman <melanieplageman@gmail.com>
Cc: Thomas Munro <thomas.munro@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, HeikkiLinnakangas <hlinnaka@iki.fi>
Date: 2020-05-29T01:14:55Z
Lists: pgsql-hackers 
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?

Regards,
	Jeff Davis

Commits

  1. Use CP_SMALL_TLIST for hash aggregate

  2. Avoid fragmentation of logical tapes when writing concurrently.