1. Lock-Free Consistency Control for Web 2.0 Applications Jiang-Ming Yang, Hai-Xun Wang, Ning Gu, Yi-Ming Liu, Chun- Song Wang, Qi-Wei Zhang 25 April 2008

2. Outline Motivation & Challenges Problem Setting Our Solutions Experiments Conclusions

3. Outline Motivation & Challenges Problem Setting Our Solutions Experiments Conclusions

4. Motivation Single Site

5. Motivation Multiple Mirror Site

6. Challenges ? ? How to merge the conflicts in Multiple Mirror Site for Web 2.0 Application?

7. Outline Motivation & Challenges Problem Setting Our Solutions Experiments Conclusions

8. Problem Setting Data shared in mirrored sites can be in varied forms. Here, we assume the shared data on mirrored sites are XML documents. Consequently, operations on the data are expressed by XML queries and updates.

9. Problem Setting CS Hot UnKnow Math

10. Problem Setting C AUSAL R ELATIONSHIPS T RANSACTIONS C ONCURRENT O PERATIONS (Lock Free)

11. Problem Setting C AUSAL R ELATIONSHIPS C AUSAL R ELATIONSHIPS U 1 Change the title Advanced Statistical Learning to Statistical Learning. U 2 Set the category of theStatistical Learning book toMath.

12. Problem Setting T RANSACTIONS T RANSACTIONS – Using transaction model to execute some critical operations – Should be executed serialized with others

13. Problem Setting C ONCURRENT O PERATIONS C ONCURRENT O PERATIONS U 3 Add a Discount tag to books inMath category. U 4 Set the category of the Linear Algebra book to CS.

14. Outline Motivation & Challenges Problem Setting Our Solutions – Causality Preservation – Transaction – Consistency Control Experiments Conclusions

15. Causality Preservation Definition. (Causal Ordering Relation ). Given two operations O a and O b from local replica sites i and j respectively, we have O a O b, if and only if (1) i = j, and O a is generated before O b is generated; (2) i j, and O a is executed on site j before O b is generated; (3) there exists an operation O x, such that O a O x and O x O b. Definition.(Concurrent Relation ). Given two operations O a and O b, we say O a and O b are concurrent or O a O b iff neither O a O b, nor O b O a.

16. Causality Preservation Vector based Timestamp – SV = – Both for Site & operation Definition. (Execution Condition). Operation O (from site i) is causally ready for execution at site j (i j) if the following conditions are satisfied: (in reference [6, 14]) – SV O [i] = SV j [i] + 1 – SV O [k] SV j [k], for all 1 k N and k i.

17. Transaction The transaction model is introduced to achieve concurrent transparency Definition. (Serialized Transaction). Let T be a transaction, and O be an operation (O may or may not be a transaction). Transaction T is a serialized transaction only if either O is executed before T in all sites, or O is executed after T in all sites.

18. Transaction O 1 NOOP 1 O 3 and O 2 NOOP 2 O 4

19. Transaction Definition. (TOrder: total order for transactions). Its a logical order among transactions : T 1 T 2 T 3 … T n.

20. Consistency Control Consistency Control – Basic Idea

21. Consistency Control - Operation XPath : /root/book XQuery & XUpdate FOR $title in /root//title $category = $book/category WHERE $title = "Advanced Statistical Learning"..

22. Consistency Control – Storage Model

25. Consistency Control - Query Process It is clear that there is no overlap in their timestamps, and at any time only one of them is valid. In general, only nodes whose timestamp (t create, t delete ) satisfies t (t create, t delete ) are valid at t.

26. Consistency Control - Query Process

27. Consistency Control – Size of OHL In our approach, we store operations in an Operation History List (OHL). Each time a replica receives a new remote operation, it will update OHL. When an operation is executed on all replicas, it will be removed from OHL and its related state information will be removed from the inverted list.

28. Outline Motivation & Challenges Problem Setting Our Solutions Experiments Conclusions

29. Experiments

32. Outline Motivation & Challenges Problem Setting Our Solutions Experiments Conclusions

33. We proposed a lock-free approach for consistency maintance in Web 2.0 environment. – We do not use the locking mechanism, so concurrent operations are executed as soon as possible upon their arrival with ensuring the convergence. – We also support the transaction semantics for critical operations without using the locking mechanism relying on the causality preservation approach. Better load balance, high-speed access and shorter respond time

34. Thank You !