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>, pgsql-hackers@postgresql.org
Date: 2020-05-21T18:19:01Z
Lists: pgsql-hackers 
On Thu, 2020-05-21 at 16:30 +0200, Tomas Vondra wrote:
> OK, it seems the attached trivial fix (simply changing CP_LABEL_TLIST
> to
> CP_SMALL_TLIST) addresses this for me.

Great!

There were a couple plan changes where it introduced a Subquery Scan.
I'm not sure that I understand why it's doing that, can you verify that
it is a reasonable thing to do?

Aside from that, feel free to commit it.

Regards,
	Jeff Davis

Commits

  1. Use CP_SMALL_TLIST for hash aggregate

  2. Avoid fragmentation of logical tapes when writing concurrently.