Interface StateStore

  • All Known Subinterfaces:
    KeyValueStore<K,​V>, SessionStore<K,​AGG>, TimestampedKeyValueStore<K,​V>, TimestampedWindowStore<K,​V>, WindowStore<K,​V>

    public interface StateStore
    A storage engine for managing state maintained by a stream processor.

    If the store is implemented as a persistent store, it must use the store name as directory name and write all data into this store directory. The store directory must be created with the state directory. The state directory can be obtained via #stateDir() using the ProcessorContext provided via init(...).

    Using nested store directories within the state directory isolates different state stores. If a state store would write into the state directory directly, it might conflict with others state stores and thus, data might get corrupted and/or Streams might fail with an error. Furthermore, Kafka Streams relies on using the store name as store directory name to perform internal cleanup tasks.

    This interface does not specify any query capabilities, which, of course, would be query engine specific. Instead it just specifies the minimum functionality required to reload a storage engine from its changelog as well as basic lifecycle management.

    • Method Detail

      • name

        String name()
        The name of this store.
        the storage name
      • flush

        void flush()
        Flush any cached data
      • close

        void close()
        Close the storage engine. Note that this function needs to be idempotent since it may be called several times on the same state store.

        Users only need to implement this function but should NEVER need to call this api explicitly as it will be called by the library automatically when necessary

      • persistent

        boolean persistent()
        Return if the storage is persistent or not.
        true if the storage is persistent—false otherwise
      • isOpen

        boolean isOpen()
        Is this store open for reading and writing
        true if the store is open