Re: Using 128-bit integers for sum, avg and statistics aggregates

From: Petr Jelinek <petr(at)2ndquadrant(dot)com>
To: Andres Freund <andres(at)2ndquadrant(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andreas Karlsson <andreas(at)proxel(dot)se>, Peter Geoghegan <pg(at)heroku(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Using 128-bit integers for sum, avg and statistics aggregates
Date: 2015-03-22 10:47:59
Message-ID: 550E9DDF.1080701@2ndquadrant.com
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On 22/03/15 10:35, Andres Freund wrote:
> On March 22, 2015 10:34:04 AM GMT+01:00, Michael Paquier <michael(dot)paquier(at)gmail(dot)com> wrote:
>> On Sun, Mar 22, 2015 at 6:22 PM, Andres Freund <andres(at)2ndquadrant(dot)com>
>>> That's due to a different patch though, right? When I checked earlier
>> only jacana had problems due to this, and it looked like random memory
>> was being output. It's interesting that that's on the one windows (not
>> cygwin) critter that does the 128bit dance...
>>
>> Yes, sorry, the e+000 stuff is from 959277a. This patch has visibly
>> broken that:
>> http://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=jacana&dt=2015-03-21%2003%3A01%3A21
>
> That's the stuff looking like random memory that I talk about above...
>

If you look at it closely, it's actually not random memory. At least in
the first 2 failing tests which are not obfuscated by aggregates on top
of aggregates. It looks like first NumericDigit is ok and the second one
is corrupted (there are only 2 NumericDigits in those numbers). Of
course the conversion to Numeric is done from the end so it looks like
only the last computation/pointer change/something stays ok while the
rest got corrupted.

--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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