From: Andres Freund <andres@anarazel.de>
To: Todd A. Cook <tcook@blackducksoftware.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: PostgreSQL Bugs <pgsql-bugs@postgresql.org>
Subject: Re: BUG #14932: SELECT DISTINCT val FROM table gets stuck in an infinite loop
Date: Tue, 28 Nov 2017 10:14:59 -0800
Message-ID: <20171128181459.d4pqmum2tjtrdwdd@alap3.anarazel.de> (raw)
In-Reply-To: <8ee9458d-1556-1cf4-9cea-ff926a9a99d5@blackducksoftware.com>
References: <20171127185700.1470.20362@wrigleys.postgresql.org>
<fd924fd9-8f27-d945-04a9-57b503896107@2ndquadrant.com>
<7a22f496-92b5-d199-984e-183965918304@blackducksoftware.com>
<20171127221041.mezzysc4zcfsqkyc@alap3.anarazel.de>
<CAEepm=3SC9zYLKhvtZbsnwf9vEpi96WCGz1rdGLofuzBau=fqA@mail.gmail.com>
<17357.1511841783@sss.pgh.pa.us>
<8ee9458d-1556-1cf4-9cea-ff926a9a99d5@blackducksoftware.com>
On 2017-11-28 09:55:13 -0500, Todd A. Cook wrote:
> On 11/27/17 23:03, Tom Lane wrote:
> >
> > Note that the sample data has a lot of collisions:
> >
> > regression=# select hashint8(val), count(*) from reproducer group by 1 order by 2 desc;
> > hashint8 | count
> > -------------+-------
> > 441526644 | 2337
> > -1117776826 | 1221
> > -1202007016 | 935
> > -2068831050 | 620
> > 1156644653 | 538
> > 553783815 | 510
> > 259780770 | 444
> > 371047036 | 394
> > 915722575 | 359
> > ... etc etc ...
>
> In case it matters, the complete data set will have some outlier values with 10k to 100k
> collisions in this column.
To make sure we're on the same page, this is data intentionally created
to have a lot of hash collisions, is that right?
Greetings,
Andres Freund
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To: pgsql-bugs@postgresql.org
Cc: andres@anarazel.de, tcook@blackducksoftware.com, tgl@sss.pgh.pa.us, thomas.munro@enterprisedb.com, tomas.vondra@2ndquadrant.com
Subject: Re: BUG #14932: SELECT DISTINCT val FROM table gets stuck in an infinite loop
In-Reply-To: <20171128181459.d4pqmum2tjtrdwdd@alap3.anarazel.de>
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