Tree-Based Consistency Approach for Cloud Databases

1. Tree-Based Consistency Approach for Cloud Databases Md. Ashfakul Islam1 and V. Vrbsky2 Department of Computer Science, The University of Alabama 1mislam@crimson.ua.edu 2vrbsky@cs.us.edu CloudCom 2010 Paper Review 2010. 09. 10 Reviewed by JaeseokMyung and Inbeom Hwang, IDS Lab., Seoul National University

2. Distributed Database • Consistency maintenance in distributed database • To maintain consistency, a replicated databasemust always communicate with other replicas,when one is ready to commit • In an unreliable network, communication neededto maintain consistency can become a bottleneck • When a node fails to respond to a message of database update • Objective • This research proposes a tree-bases system to address maintenance of consistency without performance degradation

3. Consistency Tree 0.9 0.8 0.9 0.7 0.8 0.6 0.9 0.9 Reliability of each node and each path between nodes are known Root node is the most reliable replica Uses a modified version of Dijkstra algorithm to find the most reliable path to other replicas

4. Update Operation Update Updated Updated Updated Updated Updated Updated Partially Consistent Fully Consistent • Update operation always requested to the root node first • Cf. read operation could be requested to any replicas in the graph • Partially consistent and fully consistent state • Subsequent update operation can proceed from the root node if it is in the partially consistent state • Transaction is committed when its last update operation becomes fully consistent state

5. Failure Recovery External controller rebuildsthe consistency tree when oneof its link or node goes down

6. Review • Weak reject • Simple algorithm has been presented well • But various cases are not fully covered • What if a node which is not in the global up-to-date state recovers? • How does it perform a roll-back? • No assertions • A simulation will be able to show reliability of the method