Slides for the "Server Management" workshop session on “Web Caching (6)” (session A3) facilitated by Helen Sargan and Andrew Cormack at the IWMW 1998 event held at Newcastle University on 15-17 September 1998. See http://www.ukoln.ac.uk/web-focus/events/workshops/webmaster-sep1998/materials/

1. Institutional Web Management Workshop September 1998
Information Services
Web Caching
Andrew Cormack & Helen Varley Sargan

2. Institutional Web Management Workshop September 1998
Information Services
Why cache ?
• for web users
– cache hits arrive 3-5 times faster
– 50%+ of documents are hits
– can provide licensed pages to outstations
• for network accountants
– reduction in web traffic (c.40%)
– so reduced cost
– and less congestion for others

3. Institutional Web Management Workshop September 1998
Information Services
What does it take ?
• lots of memory + fast disks
• otherwise simple systems, e.g.
– Intel CPU + Linux/FreeBSD
» 266MHz P2, 512MB memory, 40GB disk
» handles 2.5M accesses/day at Australian ISP
» 64MB, 1GB fine for 100K/day (department/small site)
– unix workstation(s)
» 2xDECAlpha, 320Mb memory, 8Gb disk (Cardiff)
– dedicated hardware
» probably only needed for large ISPs
• squid cache software is free!

4. Institutional Web Management Workshop September 1998
Information Services
What others are there ?
• national JANET Web Caching Service
– act as parent to many site caches
– prepared to act as stand-in for future site cache
– favoured access to trans-Atlantic network
– lots of information on wwwcache.ja.net
• site caches
– usually prepared to help or act as siblings
– partial list: wwwcache.ja.net/janet/contacts.html
– or join cybercache mailing list
» cybercache-request@net.loughborough.ac.uk

5. Institutional Web Management Workshop September 1998
Information Services
Cache design goals
• preparation of a user base
– to “encourage” use
– and increase hit rate
• transparency & reliability
– to prevent complaints or desertion
– ensure cache is self-explanatory
• performance
– match disk and memory provision
– more disks better than bigger ones
– cache must not swap

6. Institutional Web Management Workshop September 1998
Information Services
Cache hierarchy
• shallow to avoid excess latency
– each layer can add seconds
• group siblings with care
– “clouds” of mutual siblings are risky
– inter-sibling traffic can swamp cache
• monitor performance
– often no point in bi-directional peering
• change hierarchy to prevent staleness
– siblings tend to become similar over time
– rotate a group of siblings ?

7. Institutional Web Management Workshop September 1998
Information Services
Browser configuration
• Giving an autoconfiguration file (autoconfig.pac) is
the easiest option for users and administrators
• autoconfig.pac can be tweaked without users being
aware
• May be used by Netscape 2 and above and some
MSIE v4. Manual configuration info to be supplied
for other users
• Web proxy server should not be used for secure or
socks connections, local, *.ac.uk or .ja.net
connections

8. Institutional Web Management Workshop September 1998
Information Services
Cache politics
• network charging
– encourages caching
– but may discourage co-operation
– balance between speed and cost
• enforcing viewing policy
– must have high availability
– policy must be agreed
• access to logfiles
– privacy issues for individuals
– and institutions