Re: Caching

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

Received: from ietf.nri.reston.va.us by IETF.CNRI.Reston.VA.US id aa01375; 6 Dec 93 3:53 EST
Received: from CNRI.RESTON.VA.US by IETF.CNRI.Reston.VA.US id aa01371; 6 Dec 93 3:53 EST
Received: from mocha.bunyip.com by CNRI.Reston.VA.US id aa24274; 6 Dec 93 3:53 EST
Received: by mocha.bunyip.com (5.65a/IDA-1.4.2b/CC-Guru-2b) id AA01844 on Mon, 6 Dec 93 02:23:42 -0500
Received: from FURMINT.NECTAR.CS.CMU.EDU by mocha.bunyip.com with SMTP (5.65a/IDA-1.4.2b/CC-Guru-2b) id AA01840 (mail destined for /usr/lib/sendmail -odq -oi -fiafa-request iafa-out) on Mon, 6 Dec 93 02:23:36 -0500
Date: Mon, 06 Dec 1993 02:17:00 -0000
Sender: ietf-archive-request@IETF.CNRI.Reston.VA.US
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