Re: multi-threaded pgbench

From: Josh Williams <joshwilliams(at)ij(dot)net>
To: Greg Smith <gsmith(at)gregsmith(dot)com>
Cc: 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: 2009-07-29 21:31:53
Message-ID: 1248903114.6348.195.camel@lapdragon
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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.

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

- Josh Williams

Attachment Content-Type Size
pgbench_win32.patch text/x-patch 626 bytes

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