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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.zookeeper.server.quorum;
import java.io.IOException;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.function.BiConsumer;
import org.apache.zookeeper.server.FinalRequestProcessor;
import org.apache.zookeeper.server.Request;
import org.apache.zookeeper.server.RequestProcessor;
import org.apache.zookeeper.server.SyncRequestProcessor;
import org.apache.zookeeper.server.ZKDatabase;
import org.apache.zookeeper.server.persistence.FileTxnSnapLog;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A ZooKeeperServer for the Observer node type. Not much is different, but
* we anticipate specializing the request processors in the future.
*
*/
public class ObserverZooKeeperServer extends LearnerZooKeeperServer {
private static final Logger LOG = LoggerFactory.getLogger(ObserverZooKeeperServer.class);
/**
* Enable since request processor for writing txnlog to disk and
* take periodic snapshot. Default is ON.
*/
private boolean syncRequestProcessorEnabled = this.self.getSyncEnabled();
/*
* Pending sync requests
*/ ConcurrentLinkedQueue<Request> pendingSyncs = new ConcurrentLinkedQueue<>();
ObserverZooKeeperServer(FileTxnSnapLog logFactory, QuorumPeer self, ZKDatabase zkDb) throws IOException {
super(logFactory, self.tickTime, self.minSessionTimeout, self.maxSessionTimeout, self.clientPortListenBacklog, zkDb, self);
LOG.info("syncEnabled ={}", syncRequestProcessorEnabled);
}
public Observer getObserver() {
return self.observer;
}
@Override
public Learner getLearner() {
return self.observer;
}
/**
* Unlike a Follower, which sees a full request only during the PROPOSAL
* phase, Observers get all the data required with the INFORM packet.
* This method commits a request that has been unpacked by from an INFORM
* received from the Leader.
*
* @param request
*/
public void commitRequest(Request request) {
if (syncProcessor != null) {
// Write to txnlog and take periodic snapshot
syncProcessor.processRequest(request);
}
commitProcessor.commit(request);
}
/**
* Set up the request processors for an Observer:
* firstProcesor->commitProcessor->finalProcessor
*/
@Override
protected void setupRequestProcessors() {
// We might consider changing the processor behaviour of
// Observers to, for example, remove the disk sync requirements.
// Currently, they behave almost exactly the same as followers.
RequestProcessor finalProcessor = new FinalRequestProcessor(this);
commitProcessor = new CommitProcessor(finalProcessor, Long.toString(getServerId()), true, getZooKeeperServerListener());
commitProcessor.start();
firstProcessor = new ObserverRequestProcessor(this, commitProcessor);
((ObserverRequestProcessor) firstProcessor).start();
/*
* Observer should write to disk, so that the it won't request
* too old txn from the leader which may lead to getting an entire
* snapshot.
*
* However, this may degrade performance as it has to write to disk
* and do periodic snapshot which may double the memory requirements
*/
if (syncRequestProcessorEnabled) {
syncProcessor = new SyncRequestProcessor(this, null);
syncProcessor.start();
}
}
/*
* Process a sync request
*/
public synchronized void sync() {
if (pendingSyncs.size() == 0) {
LOG.warn("Not expecting a sync.");
return;
}
Request r = pendingSyncs.remove();
commitProcessor.commit(r);
}
@Override
public String getState() {
return "observer";
}
@Override
public void dumpMonitorValues(BiConsumer<String, Object> response) {
super.dumpMonitorValues(response);
response.accept("observer_master_id", getObserver().getLearnerMasterId());
}
}
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