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Data & Analytics · Advanced

Write-Ahead Logging (WAL)

A technique in which changes are recorded in a durable log before being applied to data files.

Definition

WAL guarantees atomicity and durability: after a crash, the database redoes committed changes and undoes uncommitted ones from the log. PostgreSQL calls it WAL, and SQL Server uses the transaction log. Shipping the log also feeds replication and point-in-time recovery.

Exam tip

WAL is what makes point-in-time recovery and streaming replication possible in PostgreSQL.

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