Software Engineering Radio - The Podcast for Professional Software Developers

Episode 496: Bruce Momjian on Multi-Version Concurrency Control in Postgres (MVCC)

This week, Postgres server developer Bruce Momjian joins host Robert Blumen for a discussion of multi-version concurrency control (MVCC) in the Postgres database. They begin with a discussion of the isolation requirement in database transactions (I in ACID); how isolation can be achieved with locking; limitations of locking; how locking limits concurrency and creates variability in query runtimes; multi-version concurrency control as a means to achieve isolation; how Postgres manages multiple versions of a row; snapshots; copy-on-write and snapshots; visibility; database transaction IDs; how tx ids, snapshots and versions interact; the need for locking when there are multiple writers; how MVCC was added to Postgres; and how to clean up unused space left over from aged-out versions.

Software Engineering Radio is a podcast targeted at the professional software developer. The goal is to be a lasting educational resource, not a newscast. Every 10 days, a new episode is published that covers all topics software engineering. Episodes are either tutorials on a specific topic, or an interview with a well-known character from the software engineering world. All SE Radio episodes are original content — we do not record conferences or talks given in other venues. Each episode comprises two speakers to ensure a lively listening experience. SE Radio is an independent and non-commercial organization. All content is licensed under the Creative Commons 2.5 license.