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本文主要研究一下artemis的SharedNothingBackupQuorum
SharedNothingBackupQuorum
activemq-artemis-2.11.0/artemis-server/src/main/java/org/apache/activemq/artemis/core/server/cluster/qourum/SharedNothingBackupQuorum.java
public class SharedNothingBackupQuorum implements Quorum, SessionFailureListener {
private TransportConfiguration liveTransportConfiguration;
public enum BACKUP_ACTIVATION {
FAIL_OVER, FAILURE_REPLICATING, ALREADY_REPLICATING, STOP;
}
private QuorumManager quorumManager;
private String targetServerID = "";
private final NodeManager nodeManager;
private final StorageManager storageManager;
private final ScheduledExecutorService scheduledPool;
private final int quorumSize;
private final int voteRetries;
private final long voteRetryWait;
private final Object voteGuard = new Object();
private CountDownLatch latch;
private ClientSessionFactoryInternal sessionFactory;
private CoreRemotingConnection connection;
private final NetworkHealthCheck networkHealthCheck;
private volatile boolean stopped = false;
private final int quorumVoteWait;
//......
@Override
public void nodeDown(Topology topology, long eventUID, String nodeID) {
if (targetServerID.equals(nodeID)) {
decideOnAction(topology);
}
}
@Override
public void nodeUp(Topology topology) {
//noop
}
/**
* if the connection to our replicated live goes down then decide on an action
*/
@Override
public void connectionFailed(ActiveMQException exception, boolean failedOver) {
decideOnAction(sessionFactory.getServerLocator().getTopology());
}
@Override
public void connectionFailed(final ActiveMQException me, boolean failedOver, String scaleDownTargetNodeID) {
connectionFailed(me, failedOver);
}
@Override
public void beforeReconnect(ActiveMQException exception) {
//noop
}
public void decideOnAction(Topology topology) {
//we may get called via multiple paths so need to guard
synchronized (decisionGuard) {
if (signal == BACKUP_ACTIVATION.FAIL_OVER) {
if (networkHealthCheck != null && !networkHealthCheck.check()) {
signal = BACKUP_ACTIVATION.FAILURE_REPLICATING;
}
return;
}
if (!isLiveDown()) {
//lost connection but don't know if live is down so restart as backup as we can't replicate any more
ActiveMQServerLogger.LOGGER.restartingAsBackupBasedOnQuorumVoteResults();
signal = BACKUP_ACTIVATION.FAILURE_REPLICATING;
} else {
// live is assumed to be down, backup fails-over
ActiveMQServerLogger.LOGGER.failingOverBasedOnQuorumVoteResults();
signal = BACKUP_ACTIVATION.FAIL_OVER;
}
/* use NetworkHealthCheck to determine if node is isolated
* if there are no addresses/urls configured then ignore and rely on quorum vote only
*/
if (networkHealthCheck != null && !networkHealthCheck.isEmpty()) {
if (networkHealthCheck.check()) {
// live is assumed to be down, backup fails-over
signal = BACKUP_ACTIVATION.FAIL_OVER;
} else {
ActiveMQServerLogger.LOGGER.serverIsolatedOnNetwork();
signal = BACKUP_ACTIVATION.FAILURE_REPLICATING;
}
}
}
latch.countDown();
}
private boolean isLiveDown() {
//lets assume live is not down
Boolean decision = false;
int voteAttempts = 0;
int size = quorumSize == -1 ? quorumManager.getMaxClusterSize() : quorumSize;
synchronized (voteGuard) {
while (!stopped && voteAttempts++ < voteRetries) {
//the live is dead so lets vote for quorum
QuorumVoteServerConnect quorumVote = new QuorumVoteServerConnect(size, targetServerID);
quorumManager.vote(quorumVote);
try {
quorumVote.await(quorumVoteWait, TimeUnit.SECONDS);
} catch (InterruptedException interruption) {
// No-op. The best the quorum can do now is to return the latest number it has
ActiveMQServerLogger.LOGGER.quorumVoteAwaitInterrupted();
}
quorumManager.voteComplete(quorumVote);
decision = quorumVote.getDecision();
if (decision) {
return decision;
}
try {
voteGuard.wait(voteRetryWait);
} catch (InterruptedException e) {
//nothing to do here
}
}
}
return decision;
}
public synchronized void reset() {
latch = new CountDownLatch(1);
}
//......
}- SharedNothingBackupQuorum的nodeDown及connectionFailed方法都会执行decideOnAction；该方法对于signal为BACKUP_ACTIVATION.FAIL_OVER的在networkHealthCheck不为null时执行networkHealthCheck.check()，若为false则更新signal为BACKUP_ACTIVATION.FAILURE_REPLICATING然后返回
- 对于signal为其他值的执行isLiveDown方法，若为false则更新signal为BACKUP_ACTIVATION.FAILURE_REPLICATING，否则更新signal为BACKUP_ACTIVATION.FAIL_OVER；最后在networkHealthCheck不为null不为空时会执行networkHealthCheck.check()，返回true则更新signal为BACKUP_ACTIVATION.FAIL_OVER，否则更新signal为BACKUP_ACTIVATION.FAILURE_REPLICATING
- isLiveDown方法创建QuorumVoteServerConnect，然后执行quorumManager.vote(quorumVote)之后进行quorumVote.await(quorumVoteWait, TimeUnit.SECONDS)，最后执行quorumManager.voteComplete(quorumVote)，然后取quorumVote.getDecision()值，若为true则立刻返回，否则执行voteGuard.wait(voteRetryWait)，进行重试，重试voteRetries次
SharedNothingBackupActivation
activemq-artemis-2.11.0/artemis-server/src/main/java/org/apache/activemq/artemis/core/server/impl/SharedNothingBackupActivation.java
public final class SharedNothingBackupActivation extends Activation {
//......
public void run() {
try {
logger.trace("SharedNothingBackupActivation..start");
synchronized (activeMQServer) {
activeMQServer.setState(ActiveMQServerImpl.SERVER_STATE.STARTED);
}
//......
synchronized (this) {
logger.trace("Entered a synchronized");
if (closed)
return;
backupQuorum = new SharedNothingBackupQuorum(activeMQServer.getStorageManager(), activeMQServer.getNodeManager(), activeMQServer.getScheduledPool(), networkHealthCheck, replicaPolicy.getQuorumSize(), replicaPolicy.getVoteRetries(), replicaPolicy.getVoteRetryWait(), replicaPolicy.getQuorumVoteWait());
activeMQServer.getClusterManager().getQuorumManager().registerQuorum(backupQuorum);
activeMQServer.getClusterManager().getQuorumManager().registerQuorumHandler(new ServerConnectVoteHandler(activeMQServer));
}
//......
SharedNothingBackupQuorum.BACKUP_ACTIVATION signal;
do {
if (closed) {
if (logger.isTraceEnabled()) {
logger.trace("Activation is closed, so giving up");
}
return;
}
if (logger.isTraceEnabled()) {
logger.trace("looking up the node through nodeLocator.locateNode()");
}
//locate the first live server to try to replicate
nodeLocator.locateNode();
Pair<TransportConfiguration, TransportConfiguration> possibleLive = nodeLocator.getLiveConfiguration();
nodeID = nodeLocator.getNodeID();
if (logger.isTraceEnabled()) {
logger.trace("nodeID = " + nodeID);
}
//in a normal (non failback) scenario if we couldn't find our live server we should fail
if (!attemptFailBack) {
if (logger.isTraceEnabled()) {
logger.trace("attemptFailback=false, nodeID=" + nodeID);
}
//this shouldn't happen
if (nodeID == null) {
logger.debug("Throwing a RuntimeException as nodeID==null ant attemptFailback=false");
throw new RuntimeException("Could not establish the connection");
}
activeMQServer.getNodeManager().setNodeID(nodeID);
}
if (possibleLive != null) {
clusterControl = tryConnectToNodeInReplicatedCluster(clusterController, possibleLive.getA());
if (clusterControl == null) {
clusterControl = tryConnectToNodeInReplicatedCluster(clusterController, possibleLive.getB());
}
} else {
clusterControl = null;
}
if (clusterControl == null) {
if (logger.isTraceEnabled()) {
logger.trace("sleeping " + clusterController.getRetryIntervalForReplicatedCluster() + " it should retry");
}
//its ok to retry here since we haven't started replication yet
//it may just be the server has gone since discovery
Thread.sleep(clusterController.getRetryIntervalForReplicatedCluster());
signal = SharedNothingBackupQuorum.BACKUP_ACTIVATION.ALREADY_REPLICATING;
continue;
}
activeMQServer.getThreadPool().execute(endpointConnector);
/**
* Wait for a signal from the the quorum manager, at this point if replication has been successful we can
* fail over or if there is an error trying to replicate (such as already replicating) we try the
* process again on the next live server. All the action happens inside {@link BackupQuorum}
*/
signal = backupQuorum.waitForStatusChange();
if (logger.isTraceEnabled()) {
logger.trace("Got a signal " + signal + " through backupQuorum.waitForStatusChange()");
}
/**
* replicationEndpoint will be holding lots of open files. Make sure they get
* closed/sync'ed.
*/
ActiveMQServerImpl.stopComponent(replicationEndpoint);
// time to give up
if (!activeMQServer.isStarted() || signal == STOP) {
if (logger.isTraceEnabled()) {
logger.trace("giving up on the activation:: activemqServer.isStarted=" + activeMQServer.isStarted() + " while signal = " + signal);
}
return;
} else if (signal == FAIL_OVER) {
// time to fail over
if (logger.isTraceEnabled()) {
logger.trace("signal == FAIL_OVER, breaking the loop");
}
break;
} else if (signal == SharedNothingBackupQuorum.BACKUP_ACTIVATION.FAILURE_REPLICATING) {
// something has gone badly run restart from scratch
if (logger.isTraceEnabled()) {
logger.trace("Starting a new thread to stop the server!");
}
Thread startThread = new Thread(new Runnable() {
@Override
public void run() {
try {
if (logger.isTraceEnabled()) {
logger.trace("Calling activeMQServer.stop() and start() to restart the server");
}
activeMQServer.stop();
activeMQServer.start();
} catch (Exception e) {
ActiveMQServerLogger.LOGGER.errorRestartingBackupServer(e, activeMQServer);
}
}
});
startThread.start();
return;
}
//ok, this live is no good, let's reset and try again
//close this session factory, we're done with it
clusterControl.close();
backupQuorum.reset();
if (replicationEndpoint.getChannel() != null) {
replicationEndpoint.getChannel().close();
replicationEndpoint.setChannel(null);
}
}
while (signal == SharedNothingBackupQuorum.BACKUP_ACTIVATION.ALREADY_REPLICATING);
//......
} catch (Exception e) {
if (logger.isTraceEnabled()) {
logger.trace(e.getMessage() + ", serverStarted=" + activeMQServer.isStarted(), e);
}
if ((e instanceof InterruptedException || e instanceof IllegalStateException) && !activeMQServer.isStarted())
// do not log these errors if the server is being stopped.
return;
ActiveMQServerLogger.LOGGER.initializationError(e);
}
}
//......
}- SharedNothingBackupActivation的run方法会创建SharedNothingBackupQuorum，然后while循环执行backupQuorum.waitForStatusChange()更新signal，直到signal不为SharedNothingBackupQuorum.BACKUP_ACTIVATION.ALREADY_REPLICATING；在signal为SharedNothingBackupQuorum.BACKUP_ACTIVATION.FAILURE_REPLICATING时执行activeMQServer.stop()及activeMQServer.start()；最后执行backupQuorum.reset()
小结
SharedNothingBackupQuorum的nodeDown及connectionFailed方法都会执行decideOnAction；该方法对于signal为BACKUP_ACTIVATION.FAIL_OVER的在networkHealthCheck不为null时执行networkHealthCheck.check()，若为false则更新signal为BACKUP_ACTIVATION.FAILURE_REPLICATING然后返回；对于signal为其他值的执行isLiveDown方法，若为false则更新signal为BACKUP_ACTIVATION.FAILURE_REPLICATING，否则更新signal为BACKUP_ACTIVATION.FAIL_OVER；最后在networkHealthCheck不为null不为空时会执行networkHealthCheck.check()，返回true则更新signal为BACKUP_ACTIVATION.FAIL_OVER，否则更新signal为BACKUP_ACTIVATION.FAILURE_REPLICATING
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