Package org.apache.druid.discovery

Interface DruidLeaderSelector

All Known Implementing Classes:
CuratorDruidLeaderSelector
public interface DruidLeaderSelector
Interface for supporting Overlord and Coordinator Leader Elections in TaskMaster and DruidCoordinator which expect appropriate implementation available in guice annotated with @IndexingService and @Coordinator respectively. Usage is as follows: On lifecycle start: druidLeaderSelector.registerListener(myListener); On lifecycle stop: druidLeaderSelector.unregisterListener();

  • Method Details

    • getCurrentLeader

      @Nullable String getCurrentLeader()
      Get ID of current Leader. Returns NULL if it can't find the leader. Note that it is possible for leadership to change right after this call returns, so caller would get wrong leader. This is expected to work even if a listener is not registered.

    • isLeader

      boolean isLeader()
      Returns true if this node is elected leader from underlying system's point of view. For example if curator is used to implement this then true would be returned when curator believes this node to be the leader. Note that it is possible for leadership to change right after this call returns, so caller would get wrong status.

    • localTerm

      int localTerm()
      Implementation would increment it everytime it becomes leader. This allows users to start a long running task when they become leader and be able to intermittently check that they are still leader from same term when they started. DruidCoordinator class uses it to do intermittent checks and stop the activity as needed.

    • registerListener

      void registerListener(DruidLeaderSelector.Listener listener)
      Register the listener for watching leadership notifications. It should only be called once.

    • unregisterListener

      void unregisterListener()
      Unregisters the listener.