Github user hanm commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/628#discussion_r230965386
--- Diff:
zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/ObserverMaster.java
---
@@ -0,0 +1,514 @@
+/**
+ * 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 org.apache.zookeeper.jmx.MBeanRegistry;
+import org.apache.zookeeper.server.Request;
+import org.apache.zookeeper.server.ZKDatabase;
+
+import java.io.BufferedInputStream;
+import java.io.ByteArrayInputStream;
+import java.io.DataInputStream;
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.net.SocketAddress;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+
+import org.apache.zookeeper.server.quorum.auth.QuorumAuthServer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Used by Followers to host Observers. This reduces the network load on
the Leader process by pushing
+ * the responsibility for keeping Observers in sync off the leading peer.
+ *
+ * It is expected that Observers will continue to perform the initial
vetting of clients and requests.
+ * Observers send the request to the follower where it is received by an
ObserverMaster.
+ *
+ * The ObserverMaster forwards a copy of the request to the ensemble
Leader and inserts it into its own
+ * request processor pipeline where it can be matched with the response
comes back. All commits received
+ * from the Leader will be forwarded along to every Learner connected to
the ObserverMaster.
+ *
+ * New Learners connecting to a Follower will receive a LearnerHandler
object and be party to its syncing logic
+ * to be brought up to date.
+ *
+ * The logic is quite a bit simpler than the corresponding logic in Leader
because it only hosts observers.
+ */
+public class ObserverMaster implements LearnerMaster, Runnable {
+ private static final Logger LOG =
LoggerFactory.getLogger(ObserverMaster.class);
+
+ //Follower counter
+ private final AtomicLong followerCounter = new AtomicLong(-1);
--- End diff --
I have a question about what variable this for. I see this value will never
get incremented, as the only function references it is
`getAndDecrementFollowerCounter`. Might worth to put more comments here.
---
