From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Jeff Davis <pgsql@j-davis.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Trouble with hashagg spill I/O pattern and costing
Date: Thu, 21 May 2020 20:54:59 +0200
Message-ID: <20200521185459.wrspycddukcztlgi@development> (raw)
In-Reply-To: <20200521183405.gq5oaarqs5gtqugt@development>
References: <20200519151202.u2p2gpiawoaznsv2@development>
<20200521134122.3rpmdolam4fgc5pv@development>
<20200521143040.zgn7ealdasfkmfcb@development>
<d1da1e990cf9d564aa435c63e1eb26748d50c10f.camel@j-davis.com>
<20200521183405.gq5oaarqs5gtqugt@development>
On Thu, May 21, 2020 at 08:34:05PM +0200, Tomas Vondra wrote:
>On Thu, May 21, 2020 at 11:19:01AM -0700, Jeff Davis wrote:
>
> ...
>
>I think we should do the pre-allocation patch too. I haven't tried yet
>but I believe the tlist fix alone won't do nearly as good.
>
I've done some measurements on the smaller (SSD) machine, and the
comparison looks like this:
sort hash hash+prealloc+tlist hash+tlist
--------------------------------------------------------
4MB 331 478 188 330
128MB 222 434 210 350
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.
I can't test this on the larger box with SATA temporary tablespace at
the moment (other tests are running), but I believe the difference will
be even more pronounced there.
I don't think we're under a lot of pressure - beta1 is out anyway, so we
have time to do proper testing first.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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To: pgsql-hackers@postgresql.org
Cc: tomas.vondra@2ndquadrant.com, pgsql@j-davis.com
Subject: Re: Trouble with hashagg spill I/O pattern and costing
In-Reply-To: <20200521185459.wrspycddukcztlgi@development>
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