Vol. I · A Postgres Handbook

The Query & the Schema

A reading-room reference for writing PostgreSQL by hand — selects to window functions, with the schema in plain view.

AdvancedAdvanced PostgreSQL

Theory: What is MVCC?

The query

SQL
-- Q: What is MVCC in PostgreSQL?
-- A: Multi-Version Concurrency Control. 
-- It ensures that readers do not block writers and writers do not block readers.
-- Instead of locking rows for reading, PostgreSQL keeps multiple versions 
-- of a row. A transaction sees a "snapshot" of data from when it started.
Tested against PostgreSQL 16

Note

“MVCC is the secret behind PostgreSQL's excellent performance under heavy concurrent loads.