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Re: multi-threaded pgbench

From: Magnus Hagander <magnus(at)hagander(dot)net>
To: Josh Williams <joshwilliams(at)ij(dot)net>
Cc: Greg Smith <gsmith(at)gregsmith(dot)com>, Itagaki Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: multi-threaded pgbench
Date: 2009-07-30 09:28:03
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Lists: pgsql-hackers
On Wed, Jul 29, 2009 at 23:31, Josh Williams<joshwilliams(at)ij(dot)net> wrote:
> On Tue, 2009-07-28 at 23:38 -0400, Josh Williams wrote:
>> Huh, running the patched version on a single thread with 128 clients
>> just got it to crash.  Actually consistently, three times now.  Will try
>> the same thing on the development box tomorrow morning to get some
>> better debugging information.
> So yeah, buffer overrun.
> In pgbench.c FD_SETSIZE is redefined to get around the Windows default
> of 64.  But this is done after bringing in winsock2.h (a couple levels
> in as a result of first including postgres_fe.h).  So any fd_set is
> built with an array of 64 descriptors, while pgbench thinks it has 1024
> available to work with.
> This was introduced a while back; the multi-threaded patch just makes it
> visible by giving it an important pointer to write over.  Previously it
> would just run over into the loop counter (and probably a couple other
> things) and thus it'd continue on happily with the [sub]set it has.

Yeah, this is fallout from the hacking we did with moving the winsock
includes around a while back. At the time the #defines were added,
winsock came in through the win32.h file :S

> In either case this seems to be a simple fix, to move that #define
> earlier (see pgbench_win32.patch.)

Yes, and it seems to be entirely unrelated to the multithreaded patch.
Thus, applied as a separate patch.

 Magnus Hagander

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