Developer Guide
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State Manager

From the ProcessContext, ReportingContext, and ControllerServiceInitializationContext, components are able to call the getStateManager() method. This State Manager is responsible for providing a simple API for storing and retrieving state. This mechanism is intended to provide developers with the ability to very easily store a set of key/value pairs, retrieve those values, and update them atomically. The state can be stored local to the node or across all nodes in a cluster. It is important to note, however, that this mechanism is intended only to provide a mechanism for storing very 'simple' state. As such, the API simply allows a Map<String, String> to be stored and retrieved and for the entire Map to be atomically replaced. Moreover, the only implementation that is currently supported for storing cluster-wide state is backed by ZooKeeper. As such, the entire State Map must be less than 1 MB in size, after being serialized. Attempting to store more than this will result in an Exception being thrown. If the interactions required by the Processor for managing state are more complex than this (e.g., large amounts of data must be stored and retrieved, or individual keys must be stored and fetched individually) than a different mechanism should be used (e.g., communicating with an external database).