@Private @Evolving

Package org.apache.hadoop.hdfs.server.federation.store

The federation state store tracks persistent values that are shared between multiple routers.

Data is stored in data records that inherit from a common class. Data records are serialized when written to the data store using a modular serialization implementation. The default is profobuf serialization. Data is stored as rows of records of the same type with each data member in a record representing a column.

The state store uses a modular data storage StateStoreDriver to handle querying, updating and deleting data records. The data storage driver is initialized and maintained by the StateStoreService. The state store supports fetching all records of a type, filtering by column values or fetching a single record by its primary key.

The state store contains several API interfaces, one for each data records type.

• MembershipStore: state of all Namenodes in the federation. Uses the MembershipState record.
• MountTableStore: Mount table mapping paths in the global namespace to individual subcluster paths. Uses the MountTable record.
• RouterStore: State of all routers in the federation. Uses the RouterState record.
• DisabledNameserviceStore: state of all disabled nameservice in the federation. Uses the DisabledNameservice record.

Each API is defined in a separate interface. The implementations of these interfaces are responsible for accessing the StateStoreDriver to query, update and delete data records.

Interface Summary

Interface	Description
StateStoreCache	Interface for a cached copy of the State Store.

Class Summary

Class	Description
CachedRecordStore<R extends BaseRecord>	Record store that takes care of caching the records in memory.
DisabledNameserviceStore	State store record to track disabled name services.
MembershipStore	Management API for NameNode registrations stored in MembershipState records.
MountTableStore	Management API for the HDFS mount table information stored in MountTable records.
RecordStore<R extends BaseRecord>	Store records in the State Store.
RouterStore	Management API for RouterState records in the state store.
StateStoreCacheUpdateService	Service to periodically update the StateStoreService cached information in the Router.
StateStoreConnectionMonitorService	Service to periodically monitor the connection of the StateStore StateStoreService data store and to re-open the connection to the data store if required.
StateStoreService	A service to initialize a StateStoreDriver and maintain the connection to the data store.
StateStoreUtils	Set of utility functions used to work with the State Store.

Exception Summary

Exception	Description
StateStoreUnavailableException	Thrown when the state store is not reachable or available.