A Robust Technique to Ensure Serializable Executions with Snapshot Isolation DBMS

Snapshot Isolation (SI) is a popular concurrency control mechanism that has been implemented by many commercial and open-source platforms (e.g. Oracle, Postgre SQL, and MS SQL Server 2005). Unfortunately, SI can result in nonserializable execution, in which database integrity constraints can be violated. The literature reports some techniques to ensure that all executions are serializable when run in an engine that uses SI for concurrency control. These modify the application by introducing conflicting SQL statements. However, with each of these techniques the DBA has to make a choice among possible transactions to modify — and as we previously showed, making a bad choice of which transactions to modify can come with a hefty performance reduction. In this paper we propose a novel technique called ELM to introduce conflicts in a separate lock-manager object. Experiments with two platforms show that ELM has peak performance which is similar to SI, no matter which transactions are chosen for modification. That is, ELM is much less vulnerable from poor DBA choices than the previous techniques.