Re: Caching

Vincent.Cate@furmint.nectar.cs.cmu.edu Mon, 06 December 1993 08:53 UTC

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Date: Mon, 6 Dec 1993 02:17-EST
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From: Vincent.Cate@furmint.nectar.cs.cmu.edu
To: iafa@bunyip.com
Subject: Re: Caching
Message-Id: <755162278/vac@FURMINT.NECTAR.CS.CMU.EDU>

Kevin:
>Vince:
>> Alex is a filesystem that gives you access to anonymous FTP files.  It
>> does do caching of files.  If the size of the file and the date last
>> modified have not changed, Alex assumes that the cached copy is still
>> good.  I don't know of any cases where this has been a problem.  The
>> real question is how often do you want to check that your cached data
>> is current.
>
>On demand verification might do the trick.

My point was just that the CRC is not really the issue.  We can tell
when a file has changed if we look.

If you check every time a file is used it still slows you way down
as you need to open up an FTP connection each time a file is used.

What I do in Alex is check if we have not checked within 1/20th the age
of the file.  So for files that have changed recently we check back
often, but for files that have not changed in 2 years we may go for a
month without checking.  User can force a check.

  -- Vince