Scalable Transactions in Partially Replicated Data Systems with Causal Snapshot Isolation

Abstract

We present here a transaction management protocol, which enhances the Partitioned Causal Snapshot Isolation (PCSI) pro- tocol, to support scalable transactions with non-local partition writes in a partially replicated multi-version database. The PCSI protocol is scalable for update transactions that involve local read and writes. However, it faces scalability limitations with non-local partition writes, when partitions are updated from any of the sites. In PCSI, to support non-local partition writes, a ghost replica of that partition is created at the transaction execution site. It is used primarily for assigning update sequence numbers to the local transactions and does not store any data. We present here an alternate approach for supporting non-local partition writes. The update sequence number for a non-local partition update is obtained from one of the remote sites that stores a replica of that partition. This approach raises several problems in regard to stalling of transactions at the remote replica’s site. We develop here a protocol based on the notion of sequence number escrow to address these problems. Through experimental evaluations, we show that this approach for supporting non-local partition updates scales almost linearly.