org.apache.solr.cloud
Class LeaderElector

java.lang.Object
  org.apache.solr.cloud.LeaderElector

public class LeaderElector
extends Object

Leader Election process. This class contains the logic by which a leader is chosen. First call * setup(ElectionContext) to ensure the election process is init'd. Next call joinElection(ElectionContext, boolean) to start the leader election. The implementation follows the classic ZooKeeper recipe of creating an ephemeral, sequential node for each candidate and then looking at the set of such nodes - if the created node is the lowest sequential node, the candidate that created the node is the leader. If not, the candidate puts a watch on the next lowest node it finds, and if that node goes down, starts the whole process over by checking if it's the lowest sequential node, etc.

Field Summary

protected SolrZkClient

zkClient

Constructor Summary

LeaderElector(SolrZkClient zkClient)

Method Summary

ElectionContext	getContext()
static String	getNodeName(String nStringSequence)
static int	getSeq(String nStringSequence) Returns int given String of form n_0000000001 or n_0000000003, etc.
int	joinElection(ElectionContext context, boolean replacement) Begin participating in the election process.
protected void	runIamLeaderProcess(ElectionContext context, boolean weAreReplacement)
void	setup(ElectionContext context) Set up any ZooKeeper nodes needed for leader election.
static void	sortSeqs(List<String> seqs) Sort n string sequence list.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

zkClient

protected SolrZkClient zkClient

Constructor Detail

LeaderElector

public LeaderElector(SolrZkClient zkClient)

Method Detail

getContext

public ElectionContext getContext()

runIamLeaderProcess

protected void runIamLeaderProcess(ElectionContext context,
                                   boolean weAreReplacement)
                            throws org.apache.zookeeper.KeeperException,
                                   InterruptedException,
                                   IOException

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

IOException

getSeq

public static int getSeq(String nStringSequence)

Returns int given String of form n_0000000001 or n_0000000003, etc.

Returns:

sequence number

getNodeName

public static String getNodeName(String nStringSequence)

joinElection

public int joinElection(ElectionContext context,
                        boolean replacement)
                 throws org.apache.zookeeper.KeeperException,
                        InterruptedException,
                        IOException

Begin participating in the election process. Gets a new sequential number and begins watching the node with the sequence number before it, unless it is the lowest number, in which case, initiates the leader process. If the node that is watched goes down, check if we are the new lowest node, else watch the next lowest numbered node.

Returns:

sequential node number

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

IOException

setup

public void setup(ElectionContext context)
           throws InterruptedException,
                  org.apache.zookeeper.KeeperException

Set up any ZooKeeper nodes needed for leader election.

Throws:

InterruptedException

org.apache.zookeeper.KeeperException

sortSeqs

public static void sortSeqs(List<String> seqs)

Sort n string sequence list.