dalesa - p2p web cache
DESCRIPTION
Dalesa P2P Web Cache (DCache). [http://www.dalesa.lk]TRANSCRIPT
- 1. Dcache: A Peer to Peer Web Cache By Wathsala Vithanage Nuwan Gunarathna Nishshanka Sirisena Lanka Software Foundation Funded by ICTA
2. Outline
- Why web caching?
3. Advantages of P2P web caching 4. Implementation 5. Problems caused by multicasting
- Solutions
Issues relevant to web caching
- Solutions
6. Outline
- Future work
7. Summary 8. Why Web Caching?
- Web requests are made to same web object multiple times by multiple users or same user
9. Caching can,
- Reduce bandwidth consumption
10. Reduce server load 11. Reduce perceived lag Web cache stores a copy of a web object with it 12. Advantages of P2P Web Caching
- Centralized server is not needed
- Can be used with existing infrastructure
- Computers already connected to the network
No need of a cache administrator
- Large network with a centralized cache needs a person to worry about it
Does not create a single point of failure
- If centralized solution fails no one access internet
13. Implementation
- Each browser becomes a node in P2P network
- Modifying an opensource browser means lot of work, therefore a proxy is used to perform caching running on each participating node.
Dalesa lightweight discovery framework search web objects on the P2P network using IP multicasting 14. Implementation 15. Problems Caused by Multicasting
- Every web request is associated with a multicast
16. If N number of nodes have already cached the file then N number of multicasts will be on the network 17. Problems Caused by Multicasting
- Problem gets bigger as N grows
- Bandwidth wasted for N 1 unwanted availability replies
18. Impaired network performance caused by network flooding 19. Solutions
- Pseudo random wait
- Wait for a random amount of time less than a threshold T before sending availability message
Piggybacking responses
- In availability message say I have not only what you have requested but also what you may need in the future
20. Solutions
- Passive Listener (PL) mode
- Learn by communication between other nodes (Difficult to deal with DHCP)
21. Issues with Web Caching
- Web object aliasing makes caching less useful
22. Web object aliasing makes redundant copies on storage devices 23. You get the same web object through different URLs
- Web objects can be mirrored in more sites
24. Web objects can be associated with a session 25. Solutions
- Cannot be solved with proxy/caches alone
26. Needs support at HTTP level 27. Servers has to be modified to implement various techniques to achieve this
- Associating URLs with hash of the web object
28. Solutions
- We will work on a possible solution
- Modifications to Dcache
29. An Apache module 30. No changes to browsers 31. Future Work
- Related to Network flooding
- Piggyback messages(In progress)
32. Pseudo random wait(In progress) In memory cache index(Not started)
- With an algorithm to load and maintain most visited cache objects (Squid already has this)
33. Future Work
- In memory object store(Not started)
- With an algorithm to load and maintain most visited cache objects (Squid has this feature)
34. Summary
- Caching improves web performance
35. P2P caches can be a viable alternative for centralized caches 36. Multicasting based P2P caches are fast compared to other types 37. Summary
- Network conditions may get impaired due to flooding but there are solutions
38. Caching is troubled by web object aliasing but solutions are not easy to implement 39. Appendix 40. Appendix