Horton

Re: BUG #14897: Segfault on statitics SQL request

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>, Michael Paquier <michael.paquier@gmail.com>, Vincent Lachenal <vincent.lachenal@gmail.com>, PostgreSQL mailing lists <pgsql-bugs@postgresql.org>
Date: 2017-11-11T17:45:12Z
Lists: pgsql-bugs 
On 2017-11-11 12:41:40 -0500, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > That's using SSE, which requires 16byte alignment IIRC.  I think we need
> > a function that properly allocate int128 vars with the right alignment -
> > don't think we want to go for full 16byte alignment for everything.
> 
> Yeah, changing MAXALIGN is out of the question.  I'm thinking about
> another flag bit for MemoryContextAllocExtended.  Do we need to think
> about other use-cases besides int128?  Should we just force 16-byte
> alignment on all architectures, or does it need to be platform-specific?

I'm not sure we want to
a) Rely on one alignment being enough for everybody.
b) Additionally burden already hot code paths with a growing number of
   alignment flag tests, and the necessary math.

How about a MemoryContextAllocAligned(context, size, alignto, flags)
that passes on most flags but adds the necessary overhead to size, and
padds the result appropriately?

Greetings,

Andres Freund

Commits

  1. Prevent int128 from requiring more than MAXALIGN alignment.

  2. Rearrange c.h to create a "compiler characteristics" section.