Write-Ahead Log
A technique where changes are written to a log before being applied to the database. Ensures durability and crash recovery.
What is Write-Ahead Log?
A technique where changes are written to a log before being applied to the database. Ensures durability and crash recovery.
Write-Ahead Log is a intermediate-level concept that sits in the Data Replication & Distribution area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "Write-Ahead Log" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
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Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
Open the Write-Ahead Log lessonRelated lessons
Lessons that touch on Write-Ahead Log as part of a larger topic.
Write-Ahead Logging
Write changes to a sequential log before applying them, the foundation of database crash recovery
advanced · consistency models
Write-Ahead Log Replication
Postgres WAL, the foundation of crash recovery, replication, and point-in-time restore
intermediate · data replication distribution
See also
Related glossary terms you might want to look up next.
ACID
Four guarantees for database transactions: Atomicity (all or nothing), Consistency (valid states only), Isolation (no interference), Durability (changes persist).
Replication
Keeping copies of the same data on multiple servers. Improves read performance and provides fault tolerance if one server goes down.
Event Sourcing
Storing every state change as an immutable event instead of just the current state. You can rebuild any past state by replaying events.