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

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Trouble with hashagg spill I/O pattern and costing
Date: 2020-05-21 19:04:19
Message-ID: 315722e3adb1eeb7f707fb649853e04c43d4711b.camel@j-davis.com
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On Thu, 2020-05-21 at 20:54 +0200, Tomas Vondra wrote:
> The last column is master with the tlist tweak alone - it's better
> than
> hashagg on master alone, but it's not nearly as good as with both
> tlist
> and prealloc patches.

Right, I certainly think we should do the prealloc change, as well.

I'm tweaking the patch to be a bit more flexible. I'm thinking we
should start the preallocation list size ~8 and then double it up to
~128 (depending on your results). That would reduce the waste in case
we have a large number of small partitions.

Regards,
Jeff Davis

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