1. 1 P2P Logging and Timestamping for Reconciliation M. Tlili, W. Dedzoe, E. Pacitti, R. Akbarinia, P. Valduriez, P. Molli, G. Canals, S. Laurière VLDB Auckland, New Zealand 2008

2. 2 Outline  Motivations  XWiki P2P Architecture  P2P-LTR service  Demonstration  Conclusion

3. 3 XWiki Application Enterprise Wiki system in OSS (LGPL) from Xpertnet, Paris Collaborative text editing among multiple users Client-server Wiki-page updating (last save wins) XWIKI Hibernate DB Client Server XWiki Client server architecture

4. 4 Motivations Problem: client-server architecture Single point of failure Hardly scalable Low mobility Etc. Solution: pure P2P architecture No central server –Scalable to millions of users Multi-Master replication Challenge: ensuring data consistency –Ensure convergence of copies –Support asynchronous updates, possibly disconnected

5. 5 XWiki P2P Application Optimistic replication Asynchronous reconciliation Yields eventual consistency Use of a DHT Efficient data location through put and get primitives Scalability Fault Tolerance through the DHT stabilization layer Handles Dynamicity (mobility) Simplify the construction of large-scale distributed applications Minimal change to XWiki code base All data remain in XWiki peers Only action logs (called patchs) are published and applied by XWiki

6. 6 XWiki P2P Replication  We propose a new mechanism of optimistic replication An algorithm for data reconciliation (So6 1,2 ) Based on operational transformation approach (OT) P2P-LTR, an extension of KTS 3,4 service Distributed continues timestamp generation Publishing operations (patchs) in DHT network 1 Ecoo Team-Project, LORIA, http://dev.libresource.orghttp://dev.libresource.org 2 P. Molli, G. Oster, H. Skaf-Molli, A. Imine. Using the transformational approach to build a safe and generic data synchronizer. ACM SIGGROUP Conference on Supporting Group Work, (GROUP),2003. 3 R. Akbarinia, E. Pacitti, P. Valduriez. Data Currency in replicated DHTs, SIGMOD 2007. 4 M. Tlili, W. K. Dedzoe, E. Pacitti, R. Akbarinia P. Valduriez, et al. P2P Logging and Timestamping for Reconciliation, Accepted demo paper in Int. Conf. on Very Large Databases (VLDB), 2008.

7. 7 So6 A configuration manager Based on OT model Uses a central timestamper To totally order the operations Disadvantages –Limited scalability –Bottleneck –Etc. Solution : P2P-LTR Generate timestamps In a fully distributed fashion

8. 8 Xwiki P2P Architecture XWiki Application XWiki Doc P2P Network XWiki Doc getLastTS retrieve Publish getPage applyPatch getPatch push Reconcile Engine (So6) Patch Service LTR DHT (OpenChord) XWiki Application

9. 9 XWiki P2P services Patch Manager Interfaces the XWiki application with replication Service Generates operations (Patch) Replication Service Performs reconciliation using OT –By retrieving consistent patches from the DHT Publishes consistent patches using P2P-LTR P2P-LTR Generates timestamps in integer serial order Stores and replicates timestamped patches in the DHT DHT Implements basic DHT primitives, based on Chord Network must be reliable with known bounds to assure consistency of routing tables 1,2 1 P.Linga et. al. Guaranteeing Correctness and Availability in P2P Range Indices. SIGMOD 2005 2 M. Bawa, A. Gionis, H. Garcia-Molina, R. Motwani: The Price of Validity in Dynamic Networks, SIGMOD 2004

10. 10 P2P-LTR for P2P editing DHT Each XWiki document is identified by a key Xwiki peer: application Master-key: generates timestamps and publishes patches in log peers Master-key succ: replaces Master-key after crash Log peer: stores timestamped patches for a key DHT = OpenChord gen_Ts getLastTS Publish

11. 11 Reconciliation with P2P-LTR Log Reconc. Engine Xwiki-Client: Post (key, patch, ts) ( 1): put(h ts (key), (patch+ts)) n Log-Peers and its successors (5): Put(h 1 (key,Last-ts),patch) Master of Key Master-Succ (5): Put(succ,last-ts) (6)ack ( 3): get missing patches and apply locally (2): ack / Last-ts ( 4): put(h ts (key), (patch,Last-ts)) (5): Put(h 3 (key,Last-ts),patch) (5): Put(h 2 (key,Last-ts),patch)

12. 12 Prototype DHT management XWiki document management Patch management Patch & Timestamp informations Network Monitoring LTR & DHT configurations

13. 13 Conclusion XWiki P2P Architecture Multi-Master replication Eventual consistency P2P-LTR Continuous timestamp generation Patch replication in DHT network Demonstration Concurrent document modification and patch publishing

14. 14 Thank you Questions?