Append-only Log
Summary: A simple, sequential data structure where new data is only appended to the end, often used for durability and replication in databases.
Sources: chapter3, chapter11
Last updated: 2026-04-18
The append-only log is one of the most fundamental data structures in data systems. Instead of updating data in place, all changes are appended to the end of a file.
Applications
- Storage Engines: Used in lsm-trees and write-ahead-log for high write throughput (source: chapter3).
- Replication: Many replication protocols use a log to ship operations from a leader to followers (source: chapter5).
- Message Brokers: log-based-message-brokers (like Apache Kafka) use a log as the primary storage and distribution mechanism (source: chapter11).
- Event Sourcing: Storing the entire history of an application as a sequence of immutable events (source: chapter11).