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 StateStoreContext.register(StateStore, StateRestoreCallback, CommitCallback) 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.

Also note that the update process of standby tasks is not monitored via this interface, since a standby task does note actually restore state, but keeps updating its state from the changelogs written by the active task which does not ever finish.

Incremental updates are exposed so users can estimate how much progress has been made.

  • 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

    • onRestoreSuspended

      default void onRestoreSuspended(TopicPartition topicPartition, String storeName, long totalRestored)
      Method called when restoring the StateStore is suspended due to the task being migrated out of the host. If the migrated task is recycled or re-assigned back to the current host, another onRestoreStart(TopicPartition, String, long, long) would be called.
      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 before being paused