Package org.apache.flink.runtime.state

Interface StateObject

All Superinterfaces:
Serializable
All Known Subinterfaces:
ChangelogStateBackendHandle, ChangelogStateHandle, CheckpointBoundKeyedStateHandle, CompositeStateHandle, IncrementalKeyedStateHandle, KeyedStateHandle, OperatorStateHandle, RetrievableStateHandle<T>, SavepointKeyedStateHandle, StreamStateHandle
All Known Implementing Classes:
AbstractChannelStateHandle, AbstractIncrementalStateHandle, ByteStreamStateHandle, ChainedStateHandle, ChangelogStateBackendHandle.ChangelogStateBackendHandleImpl, ChangelogStateBackendLocalHandle, ChangelogStateHandleStreamImpl, DirectoryStateHandle, DirectoryStreamStateHandle, EmptyFileMergingOperatorStreamStateHandle, EmptySegmentFileStateHandle, FileMergingOperatorStreamStateHandle, FileStateHandle, FinishedOperatorSubtaskState, FullyFinishedOperatorState, IncrementalLocalKeyedStateHandle, IncrementalRemoteKeyedStateHandle, InMemoryChangelogStateHandle, InputChannelStateHandle, KeyGroupsSavepointStateHandle, KeyGroupsStateHandle, OperatorState, OperatorStreamStateHandle, OperatorSubtaskState, PlaceholderStreamStateHandle, RelativeFileStateHandle, ResultSubpartitionStateHandle, RetrievableStreamStateHandle, SegmentFileStateHandle, SharedStateRegistryImpl.EmptyDiscardStateObjectForRegister, SnapshotResult, StateObjectCollection, SubtaskState, TaskState, TaskStateSnapshot
public interface StateObject extends Serializable
Base of all handles that represent checkpointed state in some form. The object may hold the (small) state directly, or contain a file path (state is in the file), or contain the metadata to access the state stored in some external database.

State objects define how to discard state and how to access the size of the state.

State Objects are transported via RPC between JobManager and TaskManager and must be serializable to support that.

Some State Objects are stored in the checkpoint/savepoint metadata. For long-term compatibility, they are not stored via Java Serialization, but through custom serializers.

  • Method Details

    • discardState

      void discardState() throws Exception
      Discards the state referred to and solemnly owned by this handle, to free up resources in the persistent storage. This method is called when the state represented by this object will not be used anymore.
      Throws:
      Exception

    • getStateSize

      long getStateSize()
      Returns the size of the state in bytes. If the size is not known, this method should return 0.

      The values produced by this method are only used for informational purposes and for metrics/monitoring. If this method returns wrong values, the checkpoints and recovery will still behave correctly. However, efficiency may be impacted (wrong space pre-allocation) and functionality that depends on metrics (like monitoring) will be impacted.

      Note for implementors: This method should not perform any I/O operations while obtaining the state size (hence it does not declare throwing an IOException). Instead, the state size should be stored in the state object, or should be computable from the state stored in this object. The reason is that this method is called frequently by several parts of the checkpointing and issuing I/O requests from this method accumulates a heavy I/O load on the storage system at higher scale.

      Returns:
      Size of the state in bytes.

    • collectSizeStats

      default void collectSizeStats(StateObject.StateObjectSizeStatsCollector collector)
      Collects statistics about state size and location from the state object.
      Parameters:
      collector - the statistics collector.