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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

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