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Date:      Wed, 14 Mar 2001 16:16:46 -0600
From:      Dan Nelson <dnelson@emsphone.com>
To:        Dag-Erling Smorgrav <des@ofug.org>
Cc:        freebsd-arch@FreeBSD.ORG, Nate Williams <nate@yogotech.com>
Subject:   Re: [PATCH] add a SITE MD5 command to ftpd
Message-ID:  <20010314161646.A1482@dan.emsphone.com>
In-Reply-To: <xzpelw0yqun.fsf@flood.ping.uio.no>; from "Dag-Erling Smorgrav" on Wed Mar 14 22:37:20 GMT 2001
References:  <20010314105918.A5204@roaming.cacheboy.net> <35525.984597779@critter> <20010314210758.A2405@roaming.cacheboy.net> <15023.53743.215996.538067@nomad.yogotech.com> <20010314130025.A3031@dragon.nuxi.com> <xzpelw0yqun.fsf@flood.ping.uio.no>

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In the last episode (Mar 14), Dag-Erling Smorgrav said:
> "David O'Brien" <TrimYourCc@NUXI.com> writes:
> > The checker can *easily* keep a list of files sizes and date stamps
> > and compare that.
> 
> Date stamps are useless. They'd be different on different master
> sites anyway. File size is almost as bad, as two files can very
> easily be totally different and still have the same size.

But how often do port distfiles change, but keep their size?  Pretty
low, I'd say, at least compared to the number of times the size changes
and the filename stays the same.

Another thing to consider before adding SITE MD5 as a command is that
it's an extremely slow operation.  md5'ing a 10MB file takes about
1/3rd of a second on my pIII/600.   It would take 5 minutes of CPU time
to md5 1-gig worth of sources, and that's assuming that the FTP server
is idle.  ftpd would have to cache the md5 checksum somewhere for it
to be acceptable, and then you've got the same caching problem (how
does ftpd know when the file has changed to is can update its cached
md5?).

-- 
	Dan Nelson
	dnelson@emsphone.com

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