kafka-streams-StateStore.adoc

StateStore Contract — State Storage Engines

StateStore is the contract of state storage engines (state stores) that store a state.

StateStore can be persistent or not (i.e. in-memory).

Table 1. StateStore Contract

Method	Description
close	void close() Closes the state store Used when: AbstractStateManager is requested to reinitializeStateStoresForPartitions GlobalStateManagerImpl and ProcessorStateManager are requested to close RocksDBStore is requested to toggleDbForBulkLoading Segments is requested to close and cleanup
flush	void flush() Flushes cached data Used when: GlobalStateManagerImpl and ProcessorStateManager are requested to flush their state stores CachingKeyValueStore, CachingSessionStore and CachingWindowStore are requested to close state stores RocksDBSegmentedBytesStore is requested to initialize the state store Segments is requested to flush
init	void init( ProcessorContext context, StateStore root) Initializes the state store Used when: AbstractStateManager is requested to reinitializeStateStoresForPartitions AbstractTask is requested to registerStateStores GlobalStateManagerImpl is requested to initialize
isOpen	boolean isOpen() Indicates whether the state store is open or not Used when: GlobalStateStoreProvider and StreamThreadStateStoreProvider are requested to stores SegmentIterator is requested to hasNext Segments is requested to segments and allSegments
name	String name() Name of the state store (for identification purposes)
persistent	boolean persistent() Indicates whether the state store is persistent (true) or not (false) Used when: GlobalStateManagerImpl is created ProcessorStateManager is requested to register a state store and checkpoint

Table 2. StateStores (Direct Extensions)

StateStore	Description
KeyValueStore
SegmentedBytesStore
SessionStore
TimeOrderedKeyValueBuffer
WindowStore
WrappedStateStore