What Is a Write‑Ahead Log (WAL), and How Does It Ensure Durability?

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What Is a Write‑Ahead Log (WAL), and How Does It Ensure Durability?

A Write-Ahead Log (WAL) is a technique where all changes are written to a separate, durable log file on disk before being applied to the main database or storage system, so that if a system crash occurs, the log can be used to recover the data and thus ensure no information is lost.

Durability is the “D” in the ACID properties of transactions. Iit means that once a transaction is committed, its changes are permanent and will survive any system failure.

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