Re: test_fsync file overrun

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: test_fsync file overrun
Date: 2009-09-21 20:21:11
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Jeff Janes wrote:
> test_fsync in tools/fsync pre-creates a 16MB file. If it is given a number
> of iterations greater than 1024 (like one might use if trying to see what
> happens when NVRAM gets filled, or on a journaling file system), than one of
> the writes being timed will have to extend the size of the pre-created test
> file, which can greatly skew the results.
> This patch uses lseek to periodically restart at the beginning of the file,
> rather than writing past the end of it.

Oh, I never noticed that the later tests kept appending to the file
rather then overwriting it. I have applied the attached fix for CVS
HEAD that just uses lseek() before each write group, as you suggested.
I have backpatched it to 8.4.X because the original code created 16GB
files in tests (yikes).

Bruce Momjian <bruce(at)momjian(dot)us>

+ If your life is a hard drive, Christ can be your backup. +

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