Re: Buildfarm failures for hash indexes: buffer leaks

On 2018-10-23 13:54:31 +0200, Fabien COELHO wrote:
>
> Hello Tom & Amit,
>
> > > > Both animals use gcc experimental versions, which may rather underline a
> > > > new bug in gcc head rather than an existing issue in pg. Or not.
> >
> > > It is possible, but what could be the possible theory?
> >
> > It seems like the two feasible theories are (1) gcc bug, or (2) buffer
> > leak that only occurs in very narrow circumstances, perhaps from a race
> > condition. Given that the hash index code hasn't changed meaningfully
> > in several months, I thought (1) seemed more probable.
>
> Yep, that is my thought as well.

FWIW, my animal 'serinus', which runs debian's gcc-snapshot shows the same problem:
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=serinus&dt=2018-10-22%2006%3A34%3A02

So it seems much more likely to be 1).

> The problem is that this kind of issue is not simple to wrap-up as a gcc bug
> report, unlike other earlier instances that I forwarded to clang & gcc dev
> teams.
>
> I'm in favor in waiting before trying to report it, to check whether the
> probable underlying gcc problem is detected, reported by someone else, and
> fixed in gcc head. If it persists, then we'll see.

I suspect the easiest thing to narrow it down would be to bisect the
problem in gcc :(

Greetings,

Andres Freund