Performance evaluation of serializable snapshot isolation in PostgreSQL

Abstract

Snapshot Isolation (SI) is a multiversion concurrency control protocol, allowing the concurrent transactions to consult older versions of the database while generating new versions using write operation. Its main advantage is to avoid the read-write conflicts, i.e. a read operation will never be blocked by a write operation and vice versa. Among existing concurrency control protocols, SI offers the highest degree of concurrency. But SI is known to be non-serializable, that is, in some situations data consistency can be violated through concurrency, even between correct applications. Recently, some extensions of SI protocol have been proposed to make it serializable. However, each of these extensions of SI admits an additional overhead to strengthen serializability. In this work, we explore the impact of the approach based on changing the SI concurrency control mechanism to ensure serializability of executions on performance. To do this, we conduct an experimental study to examine the only serializable variant of SI that is actually in use. This is the implementation of the extension Serializable Snapshot Isolation (SSI) provided in the database management system (DBMS) PostgreSQL.