Ensuring e-Transaction with Asynchronous and Uncoordinated Application Server Replicas

A recently proposed abstraction, called e-transaction (exactly-once transaction), specifies a set of properties capturing end-to-end reliability aspects for three-tier Web-based systems. In this paper we propose a distributed protocol ensuring the e-transaction properties for the general case of multiple, autonomous back-end databases. The key idea underlying our proposal consists in distributing, across the back-end tier, some recovery information reflecting the transaction processing state. This information is manipulated at low cost via local operations at the database side, with no need for any form of coordination among asynchronous replicas of the application server within the middle-tier. Compared to existing solutions, our protocol has therefore the distinguishing features of being both very light and highly scalable. The latter aspect makes our proposal particularly attractive for the case of very high degree of replication of the application access point, with distribution of the replicas within infrastructures geographically spread on public networks over the Internet (e.g., application delivery networks), namely, a configuration that also provides the advantages of reduced user perceived latency and increased system availability