HBASE-6260 balancer state should be stored in ZK

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1384593 13f79535-47bb-0310-9956-ffa450edef68

hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java

@@ -177,6 +177,7 @@ import org.apache.hadoop.hbase.util.Threads;
 import org.apache.hadoop.hbase.util.VersionInfo;
 import org.apache.hadoop.hbase.zookeeper.ClusterStatusTracker;
 import org.apache.hadoop.hbase.zookeeper.DrainingServerTracker;
+import org.apache.hadoop.hbase.zookeeper.LoadBalancerTracker;
 import org.apache.hadoop.hbase.zookeeper.RegionServerTracker;
 import org.apache.hadoop.hbase.zookeeper.ZKClusterId;
 import org.apache.hadoop.hbase.zookeeper.ZKUtil;
@@ -232,6 +233,8 @@ Server {
   private RegionServerTracker regionServerTracker;
   // Draining region server tracker
   private DrainingServerTracker drainingServerTracker;
+  // Tracker for load balancer state
+  private LoadBalancerTracker loadBalancerTracker;
 
   // RPC server for the HMaster
   private final RpcServer rpcServer;
@@ -281,8 +284,6 @@ Server {
 
   private LoadBalancer balancer;
   private Thread balancerChore;
-  // If 'true', the balancer is 'on'.  If 'false', the balancer will not run.
-  private volatile boolean balanceSwitch = true;
 
   private CatalogJanitor catalogJanitorChore;
   private LogCleaner logCleaner;
@@ -516,6 +517,8 @@ Server {
     this.catalogTracker.start();
 
     this.balancer = LoadBalancerFactory.getLoadBalancer(conf);
+    this.loadBalancerTracker = new LoadBalancerTracker(zooKeeper, this);
+    this.loadBalancerTracker.start();
     this.assignmentManager = new AssignmentManager(this, serverManager,
       this.catalogTracker, this.balancer, this.executorService, this.metrics);
     zooKeeper.registerListenerFirst(assignmentManager);
@@ -1250,7 +1253,7 @@ Server {
       return false;
     }
     // If balance not true, don't run balancer.
-    if (!this.balanceSwitch) return false;
+    if (!this.loadBalancerTracker.isBalancerOn()) return false;
     // Do this call outside of synchronized block.
     int maximumBalanceTime = getBalancerCutoffTime();
     long cutoffTime = System.currentTimeMillis() + maximumBalanceTime;
@@ -1339,19 +1342,23 @@ Server {
    * @param mode BalanceSwitchMode
    * @return old balancer switch
    */
-  public boolean switchBalancer(final boolean b, BalanceSwitchMode mode) {
+  public boolean switchBalancer(final boolean b, BalanceSwitchMode mode) throws IOException {
-    boolean oldValue = this.balanceSwitch;
+    boolean oldValue = this.loadBalancerTracker.isBalancerOn();
     boolean newValue = b;
     try {
       if (this.cpHost != null) {
         newValue = this.cpHost.preBalanceSwitch(newValue);
       }
-      if (mode == BalanceSwitchMode.SYNC) {
+      try {
-        synchronized (this.balancer) {
+        if (mode == BalanceSwitchMode.SYNC) {
-          this.balanceSwitch = newValue;
+          synchronized (this.balancer) {
+            this.loadBalancerTracker.setBalancerOn(newValue);
+          }
+        } else {
+          this.loadBalancerTracker.setBalancerOn(newValue);
         }
-      } else {
+      } catch (KeeperException ke) {
-        this.balanceSwitch = newValue;
+        throw new IOException(ke);
       }
       LOG.info("BalanceSwitch=" + newValue);
       if (this.cpHost != null) {
@@ -1363,20 +1370,24 @@ Server {
     return oldValue;
   }
 
-  public boolean synchronousBalanceSwitch(final boolean b) {
+  public boolean synchronousBalanceSwitch(final boolean b) throws IOException {
     return switchBalancer(b, BalanceSwitchMode.SYNC);
   }
 
-  public boolean balanceSwitch(final boolean b) {
+  public boolean balanceSwitch(final boolean b) throws IOException {
     return switchBalancer(b, BalanceSwitchMode.ASYNC);
   }
 
   @Override
   public SetBalancerRunningResponse setBalancerRunning(
       RpcController controller, SetBalancerRunningRequest req) throws ServiceException {
-    boolean prevValue = (req.getSynchronous())?
+    try {
-      synchronousBalanceSwitch(req.getOn()):balanceSwitch(req.getOn());
+      boolean prevValue = (req.getSynchronous())?
-    return SetBalancerRunningResponse.newBuilder().setPrevBalanceValue(prevValue).build();
+        synchronousBalanceSwitch(req.getOn()):balanceSwitch(req.getOn());
+      return SetBalancerRunningResponse.newBuilder().setPrevBalanceValue(prevValue).build();
+    } catch (IOException ioe) {
+      throw new ServiceException(ioe);
+    }
   }
 
   /**
@@ -1815,7 +1826,7 @@ Server {
       this.serverName,
       backupMasters,
       this.assignmentManager.getRegionStates().getRegionsInTransition(),
-      this.getCoprocessors(), this.balanceSwitch);
+      this.getCoprocessors(), this.loadBalancerTracker.isBalancerOn());
   }
 
   public String getClusterId() {

hbase-server/src/main/java/org/apache/hadoop/hbase/protobuf/generated/LoadBalancerProtos.java

@@ -0,0 +1,424 @@
+// Generated by the protocol buffer compiler.  DO NOT EDIT!
+// source: LoadBalancer.proto
+
+package org.apache.hadoop.hbase.protobuf.generated;
+
+public final class LoadBalancerProtos {
+  private LoadBalancerProtos() {}
+  public static void registerAllExtensions(
+      com.google.protobuf.ExtensionRegistry registry) {
+  }
+  public interface LoadBalancerStateOrBuilder
+      extends com.google.protobuf.MessageOrBuilder {
+    
+    // optional bool balancerOn = 1;
+    boolean hasBalancerOn();
+    boolean getBalancerOn();
+  }
+  public static final class LoadBalancerState extends
+      com.google.protobuf.GeneratedMessage
+      implements LoadBalancerStateOrBuilder {
+    // Use LoadBalancerState.newBuilder() to construct.
+    private LoadBalancerState(Builder builder) {
+      super(builder);
+    }
+    private LoadBalancerState(boolean noInit) {}
+    
+    private static final LoadBalancerState defaultInstance;
+    public static LoadBalancerState getDefaultInstance() {
+      return defaultInstance;
+    }
+    
+    public LoadBalancerState getDefaultInstanceForType() {
+      return defaultInstance;
+    }
+    
+    public static final com.google.protobuf.Descriptors.Descriptor
+        getDescriptor() {
+      return org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.internal_static_LoadBalancerState_descriptor;
+    }
+    
+    protected com.google.protobuf.GeneratedMessage.FieldAccessorTable
+        internalGetFieldAccessorTable() {
+      return org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.internal_static_LoadBalancerState_fieldAccessorTable;
+    }
+    
+    private int bitField0_;
+    // optional bool balancerOn = 1;
+    public static final int BALANCERON_FIELD_NUMBER = 1;
+    private boolean balancerOn_;
+    public boolean hasBalancerOn() {
+      return ((bitField0_ & 0x00000001) == 0x00000001);
+    }
+    public boolean getBalancerOn() {
+      return balancerOn_;
+    }
+    
+    private void initFields() {
+      balancerOn_ = false;
+    }
+    private byte memoizedIsInitialized = -1;
+    public final boolean isInitialized() {
+      byte isInitialized = memoizedIsInitialized;
+      if (isInitialized != -1) return isInitialized == 1;
+      
+      memoizedIsInitialized = 1;
+      return true;
+    }
+    
+    public void writeTo(com.google.protobuf.CodedOutputStream output)
+                        throws java.io.IOException {
+      getSerializedSize();
+      if (((bitField0_ & 0x00000001) == 0x00000001)) {
+        output.writeBool(1, balancerOn_);
+      }
+      getUnknownFields().writeTo(output);
+    }
+    
+    private int memoizedSerializedSize = -1;
+    public int getSerializedSize() {
+      int size = memoizedSerializedSize;
+      if (size != -1) return size;
+    
+      size = 0;
+      if (((bitField0_ & 0x00000001) == 0x00000001)) {
+        size += com.google.protobuf.CodedOutputStream
+          .computeBoolSize(1, balancerOn_);
+      }
+      size += getUnknownFields().getSerializedSize();
+      memoizedSerializedSize = size;
+      return size;
+    }
+    
+    private static final long serialVersionUID = 0L;
+    @java.lang.Override
+    protected java.lang.Object writeReplace()
+        throws java.io.ObjectStreamException {
+      return super.writeReplace();
+    }
+    
+    @java.lang.Override
+    public boolean equals(final java.lang.Object obj) {
+      if (obj == this) {
+       return true;
+      }
+      if (!(obj instanceof org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState)) {
+        return super.equals(obj);
+      }
+      org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState other = (org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState) obj;
+      
+      boolean result = true;
+      result = result && (hasBalancerOn() == other.hasBalancerOn());
+      if (hasBalancerOn()) {
+        result = result && (getBalancerOn()
+            == other.getBalancerOn());
+      }
+      result = result &&
+          getUnknownFields().equals(other.getUnknownFields());
+      return result;
+    }
+    
+    @java.lang.Override
+    public int hashCode() {
+      int hash = 41;
+      hash = (19 * hash) + getDescriptorForType().hashCode();
+      if (hasBalancerOn()) {
+        hash = (37 * hash) + BALANCERON_FIELD_NUMBER;
+        hash = (53 * hash) + hashBoolean(getBalancerOn());
+      }
+      hash = (29 * hash) + getUnknownFields().hashCode();
+      return hash;
+    }
+    
+    public static org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState parseFrom(
+        com.google.protobuf.ByteString data)
+        throws com.google.protobuf.InvalidProtocolBufferException {
+      return newBuilder().mergeFrom(data).buildParsed();
+    }
+    public static org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState parseFrom(
+        com.google.protobuf.ByteString data,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws com.google.protobuf.InvalidProtocolBufferException {
+      return newBuilder().mergeFrom(data, extensionRegistry)
+               .buildParsed();
+    }
+    public static org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState parseFrom(byte[] data)
+        throws com.google.protobuf.InvalidProtocolBufferException {
+      return newBuilder().mergeFrom(data).buildParsed();
+    }
+    public static org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState parseFrom(
+        byte[] data,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws com.google.protobuf.InvalidProtocolBufferException {
+      return newBuilder().mergeFrom(data, extensionRegistry)
+               .buildParsed();
+    }
+    public static org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState parseFrom(java.io.InputStream input)
+        throws java.io.IOException {
+      return newBuilder().mergeFrom(input).buildParsed();
+    }
+    public static org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState parseFrom(
+        java.io.InputStream input,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws java.io.IOException {
+      return newBuilder().mergeFrom(input, extensionRegistry)
+               .buildParsed();
+    }
+    public static org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState parseDelimitedFrom(java.io.InputStream input)
+        throws java.io.IOException {
+      Builder builder = newBuilder();
+      if (builder.mergeDelimitedFrom(input)) {
+        return builder.buildParsed();
+      } else {
+        return null;
+      }
+    }
+    public static org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState parseDelimitedFrom(
+        java.io.InputStream input,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws java.io.IOException {
+      Builder builder = newBuilder();
+      if (builder.mergeDelimitedFrom(input, extensionRegistry)) {
+        return builder.buildParsed();
+      } else {
+        return null;
+      }
+    }
+    public static org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState parseFrom(
+        com.google.protobuf.CodedInputStream input)
+        throws java.io.IOException {
+      return newBuilder().mergeFrom(input).buildParsed();
+    }
+    public static org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState parseFrom(
+        com.google.protobuf.CodedInputStream input,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws java.io.IOException {
+      return newBuilder().mergeFrom(input, extensionRegistry)
+               .buildParsed();
+    }
+    
+    public static Builder newBuilder() { return Builder.create(); }
+    public Builder newBuilderForType() { return newBuilder(); }
+    public static Builder newBuilder(org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState prototype) {
+      return newBuilder().mergeFrom(prototype);
+    }
+    public Builder toBuilder() { return newBuilder(this); }
+    
+    @java.lang.Override
+    protected Builder newBuilderForType(
+        com.google.protobuf.GeneratedMessage.BuilderParent parent) {
+      Builder builder = new Builder(parent);
+      return builder;
+    }
+    public static final class Builder extends
+        com.google.protobuf.GeneratedMessage.Builder<Builder>
+       implements org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerStateOrBuilder {
+      public static final com.google.protobuf.Descriptors.Descriptor
+          getDescriptor() {
+        return org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.internal_static_LoadBalancerState_descriptor;
+      }
+      
+      protected com.google.protobuf.GeneratedMessage.FieldAccessorTable
+          internalGetFieldAccessorTable() {
+        return org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.internal_static_LoadBalancerState_fieldAccessorTable;
+      }
+      
+      // Construct using org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState.newBuilder()
+      private Builder() {
+        maybeForceBuilderInitialization();
+      }
+      
+      private Builder(BuilderParent parent) {
+        super(parent);
+        maybeForceBuilderInitialization();
+      }
+      private void maybeForceBuilderInitialization() {
+        if (com.google.protobuf.GeneratedMessage.alwaysUseFieldBuilders) {
+        }
+      }
+      private static Builder create() {
+        return new Builder();
+      }
+      
+      public Builder clear() {
+        super.clear();
+        balancerOn_ = false;
+        bitField0_ = (bitField0_ & ~0x00000001);
+        return this;
+      }
+      
+      public Builder clone() {
+        return create().mergeFrom(buildPartial());
+      }
+      
+      public com.google.protobuf.Descriptors.Descriptor
+          getDescriptorForType() {
+        return org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState.getDescriptor();
+      }
+      
+      public org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState getDefaultInstanceForType() {
+        return org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState.getDefaultInstance();
+      }
+      
+      public org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState build() {
+        org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState result = buildPartial();
+        if (!result.isInitialized()) {
+          throw newUninitializedMessageException(result);
+        }
+        return result;
+      }
+      
+      private org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState buildParsed()
+          throws com.google.protobuf.InvalidProtocolBufferException {
+        org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState result = buildPartial();
+        if (!result.isInitialized()) {
+          throw newUninitializedMessageException(
+            result).asInvalidProtocolBufferException();
+        }
+        return result;
+      }
+      
+      public org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState buildPartial() {
+        org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState result = new org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState(this);
+        int from_bitField0_ = bitField0_;
+        int to_bitField0_ = 0;
+        if (((from_bitField0_ & 0x00000001) == 0x00000001)) {
+          to_bitField0_ |= 0x00000001;
+        }
+        result.balancerOn_ = balancerOn_;
+        result.bitField0_ = to_bitField0_;
+        onBuilt();
+        return result;
+      }
+      
+      public Builder mergeFrom(com.google.protobuf.Message other) {
+        if (other instanceof org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState) {
+          return mergeFrom((org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState)other);
+        } else {
+          super.mergeFrom(other);
+          return this;
+        }
+      }
+      
+      public Builder mergeFrom(org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState other) {
+        if (other == org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState.getDefaultInstance()) return this;
+        if (other.hasBalancerOn()) {
+          setBalancerOn(other.getBalancerOn());
+        }
+        this.mergeUnknownFields(other.getUnknownFields());
+        return this;
+      }
+      
+      public final boolean isInitialized() {
+        return true;
+      }
+      
+      public Builder mergeFrom(
+          com.google.protobuf.CodedInputStream input,
+          com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+          throws java.io.IOException {
+        com.google.protobuf.UnknownFieldSet.Builder unknownFields =
+          com.google.protobuf.UnknownFieldSet.newBuilder(
+            this.getUnknownFields());
+        while (true) {
+          int tag = input.readTag();
+          switch (tag) {
+            case 0:
+              this.setUnknownFields(unknownFields.build());
+              onChanged();
+              return this;
+            default: {
+              if (!parseUnknownField(input, unknownFields,
+                                     extensionRegistry, tag)) {
+                this.setUnknownFields(unknownFields.build());
+                onChanged();
+                return this;
+              }
+              break;
+            }
+            case 8: {
+              bitField0_ |= 0x00000001;
+              balancerOn_ = input.readBool();
+              break;
+            }
+          }
+        }
+      }
+      
+      private int bitField0_;
+      
+      // optional bool balancerOn = 1;
+      private boolean balancerOn_ ;
+      public boolean hasBalancerOn() {
+        return ((bitField0_ & 0x00000001) == 0x00000001);
+      }
+      public boolean getBalancerOn() {
+        return balancerOn_;
+      }
+      public Builder setBalancerOn(boolean value) {
+        bitField0_ |= 0x00000001;
+        balancerOn_ = value;
+        onChanged();
+        return this;
+      }
+      public Builder clearBalancerOn() {
+        bitField0_ = (bitField0_ & ~0x00000001);
+        balancerOn_ = false;
+        onChanged();
+        return this;
+      }
+      
+      // @@protoc_insertion_point(builder_scope:LoadBalancerState)
+    }
+    
+    static {
+      defaultInstance = new LoadBalancerState(true);
+      defaultInstance.initFields();
+    }
+    
+    // @@protoc_insertion_point(class_scope:LoadBalancerState)
+  }
+  
+  private static com.google.protobuf.Descriptors.Descriptor
+    internal_static_LoadBalancerState_descriptor;
+  private static
+    com.google.protobuf.GeneratedMessage.FieldAccessorTable
+      internal_static_LoadBalancerState_fieldAccessorTable;
+  
+  public static com.google.protobuf.Descriptors.FileDescriptor
+      getDescriptor() {
+    return descriptor;
+  }
+  private static com.google.protobuf.Descriptors.FileDescriptor
+      descriptor;
+  static {
+    java.lang.String[] descriptorData = {
+      "\n\022LoadBalancer.proto\"\'\n\021LoadBalancerStat" +
+      "e\022\022\n\nbalancerOn\030\001 \001(\010BE\n*org.apache.hado" +
+      "op.hbase.protobuf.generatedB\022LoadBalance" +
+      "rProtosH\001\240\001\001"
+    };
+    com.google.protobuf.Descriptors.FileDescriptor.InternalDescriptorAssigner assigner =
+      new com.google.protobuf.Descriptors.FileDescriptor.InternalDescriptorAssigner() {
+        public com.google.protobuf.ExtensionRegistry assignDescriptors(
+            com.google.protobuf.Descriptors.FileDescriptor root) {
+          descriptor = root;
+          internal_static_LoadBalancerState_descriptor =
+            getDescriptor().getMessageTypes().get(0);
+          internal_static_LoadBalancerState_fieldAccessorTable = new
+            com.google.protobuf.GeneratedMessage.FieldAccessorTable(
+              internal_static_LoadBalancerState_descriptor,
+              new java.lang.String[] { "BalancerOn", },
+              org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState.class,
+              org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos.LoadBalancerState.Builder.class);
+          return null;
+        }
+      };
+    com.google.protobuf.Descriptors.FileDescriptor
+      .internalBuildGeneratedFileFrom(descriptorData,
+        new com.google.protobuf.Descriptors.FileDescriptor[] {
+        }, assigner);
+  }
+  
+  // @@protoc_insertion_point(outer_class_scope)
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/zookeeper/LoadBalancerTracker.java

@@ -0,0 +1,93 @@
+/**
+ * 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.hadoop.hbase.zookeeper;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.hbase.Abortable;
+import org.apache.hadoop.hbase.DeserializationException;
+import org.apache.hadoop.hbase.protobuf.ProtobufUtil;
+import org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.zookeeper.KeeperException;
+
+import com.google.protobuf.InvalidProtocolBufferException;
+
+/**
+ * Tracks the load balancer switch up in ZK
+ */
+@InterfaceAudience.Private
+public class LoadBalancerTracker extends ZooKeeperNodeTracker {
+  private static final Log LOG = LogFactory.getLog(LoadBalancerTracker.class);
+
+  public LoadBalancerTracker(ZooKeeperWatcher watcher,
+      Abortable abortable) {
+    super(watcher, watcher.balancerZNode, abortable);
+  }
+
+  /**
+   * Return true if the balance switch is on, false otherwise
+   */
+  public boolean isBalancerOn() {
+    byte [] upData = super.getData(false);
+    try {
+      // is data in ZK is null, use default of on.
+      return upData == null || parseFrom(upData).getBalancerOn();
+    } catch (DeserializationException dex) {
+      LOG.error("ZK state for LoadBalancer could not be parsed " + Bytes.toStringBinary(upData));
+      // return false to be safe.
+      return false;
+    }
+  }
+
+  /**
+   * Set the balancer on/off
+   * @param balancerOn
+   * @throws KeeperException
+   */
+  public void setBalancerOn(boolean balancerOn) throws KeeperException {
+  byte [] upData = toByteArray(balancerOn);
+    try {
+      ZKUtil.createAndWatch(watcher, watcher.balancerZNode, upData);
+    } catch(KeeperException.NodeExistsException nee) {
+      ZKUtil.setData(watcher, watcher.balancerZNode, upData);
+    }
+  }
+
+  private byte [] toByteArray(boolean isBalancerOn) {
+    LoadBalancerProtos.LoadBalancerState.Builder builder =
+      LoadBalancerProtos.LoadBalancerState.newBuilder();
+    builder.setBalancerOn(isBalancerOn);
+    return ProtobufUtil.prependPBMagic(builder.build().toByteArray());
+  }
+
+  private LoadBalancerProtos.LoadBalancerState parseFrom(byte [] pbBytes)
+  throws DeserializationException {
+    ProtobufUtil.expectPBMagicPrefix(pbBytes);
+    LoadBalancerProtos.LoadBalancerState.Builder builder =
+      LoadBalancerProtos.LoadBalancerState.newBuilder();
+    try {
+      int magicLen = ProtobufUtil.lengthOfPBMagic();
+      builder.mergeFrom(pbBytes, magicLen, pbBytes.length - magicLen);
+    } catch (InvalidProtocolBufferException e) {
+      throw new DeserializationException(e);
+    }
+    return builder.build();
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/zookeeper/ZooKeeperWatcher.java

@@ -101,6 +101,8 @@ public class ZooKeeperWatcher implements Watcher, Abortable, Closeable {
   public String clusterIdZNode;
   // znode used for log splitting work assignment
   public String splitLogZNode;
+  // znode containing the state of the load balancer
+  public String balancerZNode;
 
   // Certain ZooKeeper nodes need to be world-readable
   public static final ArrayList<ACL> CREATOR_ALL_AND_WORLD_READABLE =
@@ -211,6 +213,8 @@ public class ZooKeeperWatcher implements Watcher, Abortable, Closeable {
         conf.get("zookeeper.znode.clusterId", "hbaseid"));
     splitLogZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.splitlog", HConstants.SPLIT_LOGDIR_NAME));
+    balancerZNode = ZKUtil.joinZNode(baseZNode,
+        conf.get("zookeeper.znode.balancer", "balancer"));
   }
 
   /**

hbase-server/src/main/protobuf/LoadBalancer.proto

@@ -0,0 +1,28 @@
+/**
+ * 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.
+ */
+
+// This file contains protocol buffers to represent the state of the load balancer.
+
+option java_package = "org.apache.hadoop.hbase.protobuf.generated";
+option java_outer_classname = "LoadBalancerProtos";
+option java_generate_equals_and_hash = true;
+option optimize_for = SPEED;
+
+message LoadBalancerState {
+  optional bool balancerOn = 1;
+}

hbase-server/src/test/java/org/apache/hadoop/hbase/master/TestMasterFailover.java

@@ -1021,6 +1021,83 @@ public class TestMasterFailover {
     TEST_UTIL.shutdownMiniCluster();
   }
 
+  /**
+   * return the index of the active master in the cluster
+   * @throws MasterNotRunningException if no active master found
+   */
+  private int getActiveMasterIndex(MiniHBaseCluster cluster) throws MasterNotRunningException {
+    // get all the master threads
+    List<MasterThread> masterThreads = cluster.getMasterThreads();
+
+    for (int i = 0; i < masterThreads.size(); i++) {
+      if (masterThreads.get(i).getMaster().isActiveMaster()) {
+        return i;
+      }
+    }
+    throw new MasterNotRunningException();
+  }
+
+  /**
+   * Kill the master and wait for a new active master to show up
+   * @param cluster
+   * @return the new active master
+   * @throws InterruptedException
+   * @throws MasterNotRunningException
+   */
+  private HMaster killActiveAndWaitForNewActive(MiniHBaseCluster cluster)
+  throws InterruptedException, MasterNotRunningException {
+    int activeIndex = getActiveMasterIndex(cluster);
+    HMaster active = cluster.getMaster();
+    cluster.stopMaster(activeIndex);
+    cluster.waitOnMaster(activeIndex);
+    assertTrue(cluster.waitForActiveAndReadyMaster());
+    // double check this is actually a new master
+    HMaster newActive = cluster.getMaster();
+    assertFalse(active == newActive);
+    return newActive;
+  }
+
+  /**
+   * Test that if the master fails, the load balancer maintains its
+   * state (running or not) when the next master takes over
+   * @throws Exception
+   */
+  @Test (timeout=240000)
+  public void testMasterFailoverBalancerPersistence() throws Exception {
+    final int NUM_MASTERS = 3;
+    final int NUM_RS = 1;
+
+    // Start the cluster
+    HBaseTestingUtility TEST_UTIL = new HBaseTestingUtility();
+
+    TEST_UTIL.startMiniCluster(NUM_MASTERS, NUM_RS);
+    MiniHBaseCluster cluster = TEST_UTIL.getHBaseCluster();
+
+    assertTrue(cluster.waitForActiveAndReadyMaster());
+    HMaster active = cluster.getMaster();
+    // check that the balancer is on by default for the active master
+    ClusterStatus clusterStatus = active.getClusterStatus();
+    assertTrue(clusterStatus.isBalancerOn());
+
+    active = killActiveAndWaitForNewActive(cluster);
+
+    // ensure the load balancer is still running on new master
+    clusterStatus = active.getClusterStatus();
+    assertTrue(clusterStatus.isBalancerOn());
+
+    // turn off the load balancer
+    active.balanceSwitch(false);
+
+    // once more, kill active master and wait for new active master to show up
+    active = killActiveAndWaitForNewActive(cluster);
+
+    // ensure the load balancer is not running on the new master
+    clusterStatus = active.getClusterStatus();
+    assertFalse(clusterStatus.isBalancerOn());
+
+    // Stop the cluster
+    TEST_UTIL.shutdownMiniCluster();
+  }
 
   @org.junit.Rule
   public org.apache.hadoop.hbase.ResourceCheckerJUnitRule cu =