Serializable Snapshot Isolation in PostgreSQL

TL;DR

This paper details the implementation and evaluation of PostgreSQL's new serializable isolation level based on Serializable Snapshot Isolation (SSI), highlighting its performance benefits and integration challenges in a production environment.

Contribution

First implementation of SSI in a production database without prior lock-based serializable support, including new lock management and performance improvements for read-only transactions.

Findings

Achieves near snapshot isolation performance

Outperforms two-phase locking on read-heavy workloads

Successfully integrates SSI with existing PostgreSQL features

Abstract

This paper describes our experience implementing PostgreSQL's new serializable isolation level. It is based on the recently-developed Serializable Snapshot Isolation (SSI) technique. This is the first implementation of SSI in a production database release as well as the first in a database that did not previously have a lock-based serializable isolation level. We reflect on our experience and describe how we overcame some of the resulting challenges, including the implementation of a new lock manager, a technique for ensuring memory usage is bounded, and integration with other PostgreSQL features. We also introduce an extension to SSI that improves performance for read-only transactions. We evaluate PostgreSQL's serializable isolation level using several benchmarks and show that it achieves performance only slightly below that of snapshot isolation, and significantly outperforms the traditional two-phase locking approach on read-intensive workloads.