Package org.apache.kafka.streams.processor

Interface StateRestoreListener

public interface StateRestoreListener

Class for listening to various states of the restoration process of a StateStore. When calling KafkaStreams.setGlobalStateRestoreListener(StateRestoreListener) the passed instance is expected to be stateless since the StateRestoreListener is shared across all StreamThread instances. Users desiring stateful operations will need to provide synchronization internally in the StateRestorerListener implementation. Note that this listener is only registered at the per-client level and users can base on the storeName parameter to define specific monitoring for different StateStores. There is another StateRestoreCallback interface which is registered via the ProcessorContext.register(StateStore, StateRestoreCallback) function per-store, and it is used to apply the fetched changelog records into the local state store during restoration. These two interfaces serve different restoration purposes and users should not try to implement both of them in a single class during state store registration. Incremental updates are exposed so users can estimate how much progress has been made.

Method Summary

Modifier and Type	Method	Description
void	onBatchRestored(TopicPartition topicPartition, String storeName, long batchEndOffset, long numRestored)	Method called after restoring a batch of records.
void	onRestoreEnd(TopicPartition topicPartition, String storeName, long totalRestored)	Method called when restoring the StateStore is complete.
void	onRestoreStart(TopicPartition topicPartition, String storeName, long startingOffset, long endingOffset)	Method called at the very beginning of StateStore restoration.

Method Details

onRestoreStart

void onRestoreStart(TopicPartition topicPartition,
 String storeName,
 long startingOffset,
 long endingOffset)

Method called at the very beginning of StateStore restoration.

Parameters:

topicPartition - the TopicPartition containing the values to restore

storeName - the name of the store undergoing restoration

startingOffset - the starting offset of the entire restoration process for this TopicPartition

endingOffset - the exclusive ending offset of the entire restoration process for this TopicPartition

onBatchRestored

void onBatchRestored(TopicPartition topicPartition,
 String storeName,
 long batchEndOffset,
 long numRestored)

Method called after restoring a batch of records. In this case the maximum size of the batch is whatever the value of the MAX_POLL_RECORDS is set to. This method is called after restoring each batch and it is advised to keep processing to a minimum. Any heavy processing will hold up recovering the next batch, hence slowing down the restore process as a whole. If you need to do any extended processing or connecting to an external service consider doing so asynchronously.

Parameters:

topicPartition - the TopicPartition containing the values to restore

storeName - the name of the store undergoing restoration

batchEndOffset - the inclusive ending offset for the current restored batch for this TopicPartition

numRestored - the total number of records restored in this batch for this TopicPartition

onRestoreEnd

void onRestoreEnd(TopicPartition topicPartition,
 String storeName,
 long totalRestored)

Method called when restoring the StateStore is complete.

Parameters:

topicPartition - the TopicPartition containing the values to restore

storeName - the name of the store just restored

totalRestored - the total number of records restored for this TopicPartition