Don’t be a Pessimist: Use Snapshot based Concurrency Control for XML

As native XML database systems (e.g., [3, 7, 8]) get increasingly popular, fine-granularity concurrency control becomes imperative in order to allow different clients to concurrently access the same documents. Existing concurrency control approaches for XML are mainly based on locking [2, 3, 4, 6, 5]. However, the experiments of [5] have shown that the locking overhead, especially for read operations, can be tremendous. In this paper, we present two snapshot based concurrency control mechanisms that avoid locking. Instead, transactions access a committed snapshot of the data.