io.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 follow. On lifecycle start: druidLeaderSelector.registerListener(myListener); On lifecycle stop: druidLeaderSelector.unregisterListener();

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	DruidLeaderSelector.Listener

Method Summary

Modifier and Type	Method and Description
String	getCurrentLeader() Get ID of current Leader.
boolean	isLeader() Returns true if this node is elected leader from underlying system's point of view.
int	localTerm() Implementation would increment it everytime it becomes leader.
void	registerListener(DruidLeaderSelector.Listener listener) Register the listener for watching leadership notifications.
void	unregisterListener() Unregisters the listener.

Method Detail

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.

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.