pg.ddx.io pgsql-docs@postgresql.org mailing list archive help / color / mirror / Atom feed From: Bruce Momjian <bruce@momjian.us>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: David Rowley <dgrowleyml@gmail.com>
Cc: Jeff Davis <pgsql@j-davis.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>
Cc: Melanie Plageman <melanieplageman@gmail.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: Default setting for enable_hashagg_disk
Date: Mon, 29 Jun 2020 13:31:40 -0400
Message-ID: <20200629173140.GE17529@momjian.us> (raw )
In-Reply-To: <CAH2-WzmnaKVmZFNzcwAyGzvetLTO_aHkVVptMaBQ-gv1OjFh2g@mail.gmail.com >
References: <20200626144414.rftlidu34rigiulv@development >
<20200626163726.GA3337@momjian.us >
<20200626174513.tmnkic7q5duugvhh@development >
<20200626230020.GD3337@momjian.us >
<20200626235850.gvl3lpfyeobu4evi@development >
<CAH2-Wz=osB4oi_nH8MnosYhVVSNOm5q3=exGe-b3q6gWOgf98w@mail.gmail.com >
<20200627104141.gq7d3hm2tvoqgjjs@development >
<CAH2-Wzn6M7FwwgXe-mSnmCuMuF9OnFZW=m0X6JMOEYt4VfJTgQ@mail.gmail.com >
<20200629150655.ethstxkf3bkqoown@development >
<CAH2-WzmnaKVmZFNzcwAyGzvetLTO_aHkVVptMaBQ-gv1OjFh2g@mail.gmail.com >
On Mon, Jun 29, 2020 at 10:20:14AM -0700, Peter Geoghegan wrote:
> I have no reason to believe that the planner is any more or any less
> likely to conclude that the hash table will fit in memory in v13 as
> things stand (I don't know if the BufFile issue matters).
>
> In general, grouping estimates probably aren't very good compared to
> join estimates. I imagine that in either v12 or v13 the planner is
> likely to incorrectly believe that it'll all fit in memory fairly
> often. v12 was much too permissive about what could happen. But v13 is
> too conservative.
FYI, we have improved planner statistics estimates for years, which must
have affected node spill behavior on many node types (except hash_agg),
and don't remember any complaints about it.
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EnterpriseDB https://enterprisedb.com
The usefulness of a cup is in its emptiness, Bruce Lee
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Cc: bruce@momjian.us, pg@bowt.ie, tomas.vondra@2ndquadrant.com, robertmhaas@gmail.com, andres@anarazel.de, dgrowleyml@gmail.com, pgsql@j-davis.com, pryzby@telsasoft.com, melanieplageman@gmail.com, pgsql-hackers@postgresql.org
Subject: Re: Default setting for enable_hashagg_disk
In-Reply-To: <20200629173140.GE17529@momjian.us>
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