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.

IntermediateAdvanced PostgreSQL

Theory: What is WAL?

The query

SQL
-- Q: What is WAL (Write-Ahead Logging)?
-- A: A standard method for ensuring data integrity. 
-- Changes to data files must be written to the WAL log *before* 
-- they are applied to the actual data files. If the database crashes, 
-- it recovers by replaying the WAL logs to restore the state.
Tested against PostgreSQL 16

Note

“WAL is crucial for Crash Recovery and Point-In-Time Recovery (PITR).