Changelog
A changelog topic is a Kafka topic that records state-store updates so processing state can be recovered or restored.
Kafka Streams in Action, Second Edition
A changelog is an append-oriented record sequence that retains the latest record for each key.
- How it is used
- Supports durable state and update-stream modeling for Kafka Streams stateful processing.
- How deep it goes
- Explains latest-per-key semantics, compaction, restoration, caching, naming, and per-topic configuration.
- Examples
- Uses keyed customer purchases and a grouped count with a named materialized state store.
- What you can do after
- Operate/configure changelog-backed state stores by naming stores, tuning cleanup, and retaining logging.
Read how Kafka Streams in Action, Second Edition explains changelog →
Apache Kafka in Action
A changelog topic is an internal Kafka topic that durably records updates to processing state so the state can be restored after a failure.
- How it is used
- Preserves local table and aggregation state so Kafka Streams can restore it after an instance fails.
- How deep it goes
- Explains update writes and restoration by reading the topic, but does not specify changelog record formats or restoration commands.
- Examples
- Illustrates a per-key count state store and its compacted changelog, then describes takeover by another instance.
- What you can do after
- Diagnose/debug with it by identifying why a replacement task rebuilds state, or configure standby replicas to avoid that rebuild.
Related concepts
- compacted topickind of · A compacted topic is a Kafka topic whose log compaction retains the latest record for each key while allowing obsolete records to be removed.
- state storeused by · A state store is a storage component that maintains application or processing state and provides mechanisms to access or update it.
- standby taskused by · A standby task is an inactive Kafka Streams task that maintains a replicated state-store copy for faster failover when an active task is reassigned.
- logcontrasts with · A log is a record of events, activity, or diagnostic information produced during the operation of a system or process, often ordered by time.
- KTableused by · KTable is a Kafka Streams abstraction representing the latest value associated with each key as a continuously updated table.
- in-memory databaseused by · An in-memory database is a database whose primary working data resides in main memory rather than primarily in persistent storage.
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