Lock-free consistency control for web 2.0 applications

Online collaboration and sharing is the central theme of many web-based services that create the so-called Web 2.0 phenomena. Using the Internet as a computing platform, many Web 2.0 applications set up mirror sites to provide large-scale availability and to achieve load balance. However, in the age of Web 2.0, where every user is also a writer and publisher, the deployment of mirror sites makes consistency maintenance a Web scale problem. Traditional concurrency control methods (e.g. two phase lock, serialization, etc.) are not up to the task for several reasons. First, large network latency between mirror sites will make two phase locking a throughput bottleneck. Second, locking will block a large portion of concurrent operations, which makes it impossible to provide large-scale availability. On the other hand, most Web 2.0 operations do not need strict serializability - it is not the intention of a user who is correcting a typo in a shared document to block another who is adding a comment, as long as consistency can still be achieved. Thus, in order to enable maximal online collaboration and sharing, we need a lock-free mechanism that can maintain consistency among mirror sites on the Web. In this paper, we propose a flexible and efficient method to achieve consistency maintenance in the Web 2.0 world. Our experiments show its good performance improvement compared with existing methods based on distributed lock.