Package org.apache.flink.api.connector.source

Interface SplitEnumerator<SplitT extends SourceSplit,CheckpointT>

All Superinterfaces:

AutoCloseable, CheckpointListener

All Known Implementing Classes:

IteratorSourceEnumerator

@Public
public interface SplitEnumerator<SplitT extends SourceSplit,CheckpointT>
extends AutoCloseable, CheckpointListener

The interface for a split enumerator responsible for discovering the source splits, and assigning them to the SourceReader.

Method Summary

Modifier and Type	Method	Description
void	addReader(int subtaskId)	Add a new source reader with the given subtask ID.
void	addSplitsBack(List<SplitT> splits, int subtaskId)	Add splits back to the split enumerator.
void	close()	Called to close the enumerator, in case it holds on to any resources, like threads or network connections.
default void	handleSourceEvent(int subtaskId, SourceEvent sourceEvent)	Handles a custom source event from the source reader.
void	handleSplitRequest(int subtaskId, String requesterHostname)	Handles the request for a split.
default void	notifyCheckpointComplete(long checkpointId)	We have an empty default implementation here because most source readers do not have to implement the method.
CheckpointT	snapshotState(long checkpointId)	Creates a snapshot of the state of this split enumerator, to be stored in a checkpoint.
void	start()	Start the split enumerator.

Methods inherited from interface org.apache.flink.api.common.state.CheckpointListener

notifyCheckpointAborted

Method Detail

start

void start()

Start the split enumerator.

The default behavior does nothing.

handleSplitRequest

void handleSplitRequest(int subtaskId,
                        @Nullable
                        String requesterHostname)

Handles the request for a split. This method is called when the reader with the given subtask id calls the SourceReaderContext.sendSplitRequest() method.

Parameters:

subtaskId - the subtask id of the source reader who sent the source event.

requesterHostname - Optional, the hostname where the requesting task is running. This can be used to make split assignments locality-aware.

addSplitsBack

void addSplitsBack(List<SplitT> splits,
                   int subtaskId)

Add splits back to the split enumerator. This will only happen when a SourceReader fails and there are splits assigned to it after the last successful checkpoint.

Parameters:

splits - The splits to add back to the enumerator for reassignment.

subtaskId - The id of the subtask to which the returned splits belong.

addReader

void addReader(int subtaskId)

Add a new source reader with the given subtask ID.

Parameters:

subtaskId - the subtask ID of the new source reader.

snapshotState

CheckpointT snapshotState(long checkpointId)
                   throws Exception

Creates a snapshot of the state of this split enumerator, to be stored in a checkpoint.

The snapshot should contain the latest state of the enumerator: It should assume that all operations that happened before the snapshot have successfully completed. For example all splits assigned to readers via SplitEnumeratorContext.assignSplit(SourceSplit, int) and SplitEnumeratorContext.assignSplits(SplitsAssignment)) don't need to be included in the snapshot anymore.

This method takes the ID of the checkpoint for which the state is snapshotted. Most implementations should be able to ignore this parameter, because for the contents of the snapshot, it doesn't matter for which checkpoint it gets created. This parameter can be interesting for source connectors with external systems where those systems are themselves aware of checkpoints; for example in cases where the enumerator notifies that system about a specific checkpoint being triggered.

Parameters:

checkpointId - The ID of the checkpoint for which the snapshot is created.

Returns:

an object containing the state of the split enumerator.

Throws:

Exception - when the snapshot cannot be taken.

close

void close()
    throws IOException

Called to close the enumerator, in case it holds on to any resources, like threads or network connections.

Specified by:

close in interface AutoCloseable

Throws:

IOException

notifyCheckpointComplete

default void notifyCheckpointComplete(long checkpointId)
                               throws Exception

We have an empty default implementation here because most source readers do not have to implement the method.

Specified by:

notifyCheckpointComplete in interface CheckpointListener

Parameters:

checkpointId - The ID of the checkpoint that has been completed.

Throws:

Exception - This method can propagate exceptions, which leads to a failure/recovery for the task. Note that this will NOT lead to the checkpoint being revoked.

See Also:

CheckpointListener.notifyCheckpointComplete(long)

handleSourceEvent

default void handleSourceEvent(int subtaskId,
                               SourceEvent sourceEvent)

Handles a custom source event from the source reader.

This method has a default implementation that does nothing, because it is only required to be implemented by some sources, which have a custom event protocol between reader and enumerator. The common events for reader registration and split requests are not dispatched to this method, but rather invoke the addReader(int) and handleSplitRequest(int, String) methods.

Parameters:

subtaskId - the subtask id of the source reader who sent the source event.

sourceEvent - the source event from the source reader.