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Date:      Thu, 20 May 1999 11:30:21 -0500 (CDT)
From:      James Wyatt <jwyatt@RWSystems.net>
To:        Roger Marquis <marquis@roble.com>
Cc:        freebsd-isp@FreeBSD.ORG
Subject:   Re: Web Statistics break up program.
Message-ID:  <Pine.BSF.4.05.9905201115020.18069-100000@kasie.rwsystems.net>
In-Reply-To: <Pine.GSO.3.96.990518195705.24618B-100000@roble2.roble.com>

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On Tue, 18 May 1999, Roger Marquis wrote:
> > > This will create an archived logfile (http.site.May_1999) and erase
> > > the original without needing to kill -1 the httpd.
> > > 
> > > 	#!/bin/sh -
> > > 	LOGDIR=/var/log
> > > 	ARCDIR=/var/log/oldlogs
> > > 	DAY=`date | awk '{ OFS="_" ;print $2,$6}' `
> > > 	for log in $LOGDIR/http* ; do
> > > 		cp $log $ARCDIR/${log}.${DAY}
> > > 		chmod 440 $ARCDIR/${log}.${DAY}
> > > 		cp /dev/null $log
> > > 	done
> > 
> > Egads!!
> > That's a pretty vicious race condition there, you'll lose records on busy
> > servers.
> 
> In theory perhaps, in reality it doesn't.  I've never seen this algorithm 
> fail, even when used on log files that grow by several megabytes per day.

Since you would quietly lose just a few lines once-in-a-while during a low
traffic period, how would you *know*? The server I'm most concerned about
handles eCommerce for transportation. It has logs of about 40-50MB/day.

This looks like a noticable race condition on most platforms. I would like
to know why it doesn't happen if it doesn't. Sounds like I have some
playing to do some evening. - Jy@

Wyatts law: The difference between theory and practise is larger in
practise than in theory.



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