Class FastLeaderElection
- java.lang.Object
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- org.apache.zookeeper.server.quorum.FastLeaderElection
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- All Implemented Interfaces:
Election
public class FastLeaderElection extends Object implements Election
Implementation of leader election using TCP. It uses an object of the class QuorumCnxManager to manage connections. Otherwise, the algorithm is push-based as with the other UDP implementations. There are a few parameters that can be tuned to change its behavior. First, finalizeWait determines the amount of time to wait until deciding upon a leader. This is part of the leader election algorithm.
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Nested Class Summary
Nested Classes Modifier and Type Class Description protected classFastLeaderElection.MessengerMulti-threaded implementation of message handler.static classFastLeaderElection.NotificationNotifications are messages that let other peers know that a given peer has changed its vote, either because it has joined leader election or because it learned of another peer with higher zxid or same zxid and higher server idstatic classFastLeaderElection.ToSendMessages that a peer wants to send to other peers.
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Field Summary
Fields Modifier and Type Field Description static StringMAX_NOTIFICATION_INTERVALMaximum notification interval, default is 60sstatic StringMIN_NOTIFICATION_INTERVALMinimum notification interval, default is equal to finalizeWait
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Constructor Summary
Constructors Constructor Description FastLeaderElection(QuorumPeer self, QuorumCnxManager manager)Constructor of FastLeaderElection.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description protected booleancheckLeader(Map<Long,Vote> votes, long leader, long electionEpoch)In the case there is a leader elected, and a quorum supporting this leader, we have to check if the leader has voted and acked that it is leading.QuorumCnxManagergetCnxManager()longgetLogicalClock()Returns the current value of the logical clock counterVotegetVote()protected SyncedLearnerTrackergetVoteTracker(Map<Long,Vote> votes, Vote vote)Given a set of votes, return the SyncedLearnerTracker which is used to determines if have sufficient to declare the end of the election round.VotelookForLeader()Starts a new round of leader election.voidshutdown()voidstart()This method starts the sender and receiver threads.protected booleantotalOrderPredicate(long newId, long newZxid, long newEpoch, long curId, long curZxid, long curEpoch)Check if a pair (server id, zxid) succeeds our current vote.
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Field Detail
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MIN_NOTIFICATION_INTERVAL
public static final String MIN_NOTIFICATION_INTERVAL
Minimum notification interval, default is equal to finalizeWait- See Also:
- Constant Field Values
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MAX_NOTIFICATION_INTERVAL
public static final String MAX_NOTIFICATION_INTERVAL
Maximum notification interval, default is 60s- See Also:
- Constant Field Values
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Constructor Detail
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FastLeaderElection
public FastLeaderElection(QuorumPeer self, QuorumCnxManager manager)
Constructor of FastLeaderElection. It takes two parameters, one is the QuorumPeer object that instantiated this object, and the other is the connection manager. Such an object should be created only once by each peer during an instance of the ZooKeeper service.- Parameters:
self- QuorumPeer that created this objectmanager- Connection manager
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Method Detail
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getLogicalClock
public long getLogicalClock()
Returns the current value of the logical clock counter
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start
public void start()
This method starts the sender and receiver threads.
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getCnxManager
public QuorumCnxManager getCnxManager()
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totalOrderPredicate
protected boolean totalOrderPredicate(long newId, long newZxid, long newEpoch, long curId, long curZxid, long curEpoch)Check if a pair (server id, zxid) succeeds our current vote.
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getVoteTracker
protected SyncedLearnerTracker getVoteTracker(Map<Long,Vote> votes, Vote vote)
Given a set of votes, return the SyncedLearnerTracker which is used to determines if have sufficient to declare the end of the election round.- Parameters:
votes- Set of votesvote- Identifier of the vote received last- Returns:
- the SyncedLearnerTracker with vote details
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checkLeader
protected boolean checkLeader(Map<Long,Vote> votes, long leader, long electionEpoch)
In the case there is a leader elected, and a quorum supporting this leader, we have to check if the leader has voted and acked that it is leading. We need this check to avoid that peers keep electing over and over a peer that has crashed and it is no longer leading.- Parameters:
votes- set of votesleader- leader idelectionEpoch- epoch id
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getVote
public Vote getVote()
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lookForLeader
public Vote lookForLeader() throws InterruptedException
Starts a new round of leader election. Whenever our QuorumPeer changes its state to LOOKING, this method is invoked, and it sends notifications to all other peers.- Specified by:
lookForLeaderin interfaceElection- Throws:
InterruptedException
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