State store
A state store is a storage component that maintains application or processing state and provides mechanisms to access or update it.
Kafka Streams in Action, Second Edition
A state store is a Kafka Streams component that persistently maintains intermediate processing state for an application.
- How it is used
- Supports stateful Kafka Streams operations and custom processors that retain per-key results over time.
- How deep it goes
- Explains store types, changelog restoration, task ownership, filesystem placement, naming, querying, custom access, and tests without detailing storage-engine internals.
- Examples
- Uses a key count, a filtered topology, stock-performance analysis, loan rollups, and poker-score reduction tests.
- What you can do after
- Operate/configure stateful Kafka Streams applications with stable store names, appropriate store types, query access, and store-level tests.
Read how Kafka Streams in Action, Second Edition explains state store →
Kafka for Architects
A local state store is a stateful storage mechanism located on the same node as processing logic for low-latency access to application state.
- How it is used
- Maintains locally accessible state for low-latency event enrichment, joins, and aggregations.
- How deep it goes
- Explains keyed storage, task ownership, changelog recovery, and query routing, while leaving remote-query implementation to the application.
- Examples
- Uses customer-data lookups for order enrichment and per-region counters for order aggregation.
- What you can do after
- Operate/configure it by planning storage and restoration capacity and distinguishing local queries from application-implemented remote queries.
Apache Kafka in Action
A Kafka Streams state store is a local storage component that maintains processing state for a stream-processing application.
- How it is used
- Supports task-local processing state while Kafka Streams scales work across threads and application instances.
- How deep it goes
- Explains task ownership, changelog rebuilding, standby replicas, and RocksDB metrics, but not store construction or query APIs.
- Examples
- Uses a nine-task deployment, instance failure, changelog restoration, standby copies, and RocksDB memory-table metrics.
- What you can do after
- Diagnose state-related scaling and recovery behavior using task assignments, changelog rebuilding, standby replicas, and store metrics.
Related concepts
- interactive queryused by · An interactive query is a query that returns results immediately from currently accessible data or application state.
- changeloguses · A changelog topic is a Kafka topic that records state-store updates so processing state can be recovered or restored.
- taskpart of · A Kafka Streams task is an independently executable processing unit that processes assigned input partitions through a topology and its associated state stores.
- key-value storekind of · A key-value store is a data-storage system that associates keys with values and supports storing, retrieving, or updating values by key.
- statefulnessused by · Statefulness is the property of a system or operation whose behavior or results depend on information retained or changed across interactions or executions.
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