From: | Petr Jelinek <petr(at)2ndquadrant(dot)com> |
---|---|
To: | Andreas Karlsson <andreas(at)proxel(dot)se>, 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>, 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 21:00:13 |
Message-ID: | 550F2D5D.9080700@2ndquadrant.com |
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Lists: | pgsql-hackers |
On 22/03/15 13:59, Andreas Karlsson wrote:
> On 03/22/2015 11:47 AM, Petr Jelinek wrote:
>> On 22/03/15 10:35, Andres Freund wrote:
>>>> 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.
>
> Would this mean the bug is most likely somewhere in
> int128_to_numericvar()? Maybe that version of gcc has a bug in some
> __int128 operator or I messed up the code there somehow.
>
Yeah that's what I was thinking also, and I went through the function
and didn't find anything suspicious (besides it's same as the 64 bit
version except for the int128 use).
It really might be some combination of arithmetic + the conversion to
16bit uint bug in the compiler. Would be worth to try to produce test
case and try it standalone maybe?
--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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