[48/54] [partial] ACCUMULO-658, ACCUMULO-656 Split server into separate modules

[ct...@apache.org]

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/LiveTServerSet.java
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diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/LiveTServerSet.java b/server/base/src/main/java/org/apache/accumulo/server/master/LiveTServerSet.java
new file mode 100644
index 0000000..3eef065
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/LiveTServerSet.java
@@ -0,0 +1,399 @@
+/*
+ * 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.accumulo.server.master;
+
+import static org.apache.accumulo.fate.zookeeper.ZooUtil.NodeMissingPolicy.SKIP;
+
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+import org.apache.accumulo.core.Constants;
+import org.apache.accumulo.core.client.Instance;
+import org.apache.accumulo.core.client.impl.thrift.ThriftSecurityException;
+import org.apache.accumulo.core.conf.AccumuloConfiguration;
+import org.apache.accumulo.core.data.KeyExtent;
+import org.apache.accumulo.core.master.thrift.TabletServerStatus;
+import org.apache.accumulo.core.tabletserver.thrift.NotServingTabletException;
+import org.apache.accumulo.core.tabletserver.thrift.TabletClientService;
+import org.apache.accumulo.core.util.AddressUtil;
+import org.apache.accumulo.core.util.ServerServices;
+import org.apache.accumulo.core.util.ThriftUtil;
+import org.apache.accumulo.core.zookeeper.ZooUtil;
+import org.apache.accumulo.server.master.state.TServerInstance;
+import org.apache.accumulo.server.security.SystemCredentials;
+import org.apache.accumulo.server.util.Halt;
+import org.apache.accumulo.server.util.time.SimpleTimer;
+import org.apache.accumulo.server.zookeeper.ZooCache;
+import org.apache.accumulo.server.zookeeper.ZooLock;
+import org.apache.accumulo.server.zookeeper.ZooReaderWriter;
+import org.apache.accumulo.trace.instrument.Tracer;
+import org.apache.hadoop.io.Text;
+import org.apache.log4j.Logger;
+import org.apache.thrift.TException;
+import org.apache.thrift.transport.TTransport;
+import org.apache.zookeeper.KeeperException;
+import org.apache.zookeeper.KeeperException.NoNodeException;
+import org.apache.zookeeper.KeeperException.NotEmptyException;
+import org.apache.zookeeper.WatchedEvent;
+import org.apache.zookeeper.Watcher;
+import org.apache.zookeeper.data.Stat;
+
+import com.google.common.net.HostAndPort;
+
+public class LiveTServerSet implements Watcher {
+  
+  public interface Listener {
+    void update(LiveTServerSet current, Set<TServerInstance> deleted, Set<TServerInstance> added);
+  }
+  
+  private static final Logger log = Logger.getLogger(LiveTServerSet.class);
+  
+  private final Listener cback;
+  private final Instance instance;
+  private final AccumuloConfiguration conf;
+  private ZooCache zooCache;
+  
+  public class TServerConnection {
+    private final HostAndPort address;
+    
+    public TServerConnection(HostAndPort addr) throws TException {
+      address = addr;
+    }
+    
+    private String lockString(ZooLock mlock) {
+      return mlock.getLockID().serialize(ZooUtil.getRoot(instance) + Constants.ZMASTER_LOCK);
+    }
+    
+    public void assignTablet(ZooLock lock, KeyExtent extent) throws TException {
+      TabletClientService.Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), address, conf);
+      try {
+        client.loadTablet(Tracer.traceInfo(), SystemCredentials.get().toThrift(instance), lockString(lock), extent.toThrift());
+      } finally {
+        ThriftUtil.returnClient(client);
+      }
+    }
+    
+    public void unloadTablet(ZooLock lock, KeyExtent extent, boolean save) throws TException {
+      TabletClientService.Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), address, conf);
+      try {
+        client.unloadTablet(Tracer.traceInfo(), SystemCredentials.get().toThrift(instance), lockString(lock), extent.toThrift(), save);
+      } finally {
+        ThriftUtil.returnClient(client);
+      }
+    }
+    
+    public TabletServerStatus getTableMap(boolean usePooledConnection) throws TException, ThriftSecurityException {
+      
+      if (usePooledConnection == true)
+        throw new UnsupportedOperationException();
+      
+      TTransport transport = ThriftUtil.createTransport(address, conf);
+      
+      try {
+        TabletClientService.Client client = ThriftUtil.createClient(new TabletClientService.Client.Factory(), transport);
+        return client.getTabletServerStatus(Tracer.traceInfo(), SystemCredentials.get().toThrift(instance));
+      } finally {
+        if (transport != null)
+          transport.close();
+      }
+    }
+    
+    public void halt(ZooLock lock) throws TException, ThriftSecurityException {
+      TabletClientService.Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), address, conf);
+      try {
+        client.halt(Tracer.traceInfo(), SystemCredentials.get().toThrift(instance), lockString(lock));
+      } finally {
+        ThriftUtil.returnClient(client);
+      }
+    }
+    
+    public void fastHalt(ZooLock lock) throws TException {
+      TabletClientService.Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), address, conf);
+      try {
+        client.fastHalt(Tracer.traceInfo(), SystemCredentials.get().toThrift(instance), lockString(lock));
+      } finally {
+        ThriftUtil.returnClient(client);
+      }
+    }
+    
+    public void flush(ZooLock lock, String tableId, byte[] startRow, byte[] endRow) throws TException {
+      TabletClientService.Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), address, conf);
+      try {
+        client.flush(Tracer.traceInfo(), SystemCredentials.get().toThrift(instance), lockString(lock), tableId,
+            startRow == null ? null : ByteBuffer.wrap(startRow), endRow == null ? null : ByteBuffer.wrap(endRow));
+      } finally {
+        ThriftUtil.returnClient(client);
+      }
+    }
+    
+    public void chop(ZooLock lock, KeyExtent extent) throws TException {
+      TabletClientService.Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), address, conf);
+      try {
+        client.chop(Tracer.traceInfo(), SystemCredentials.get().toThrift(instance), lockString(lock), extent.toThrift());
+      } finally {
+        ThriftUtil.returnClient(client);
+      }
+    }
+    
+    public void splitTablet(ZooLock lock, KeyExtent extent, Text splitPoint) throws TException, ThriftSecurityException, NotServingTabletException {
+      TabletClientService.Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), address, conf);
+      try {
+        client.splitTablet(Tracer.traceInfo(), SystemCredentials.get().toThrift(instance), extent.toThrift(),
+            ByteBuffer.wrap(splitPoint.getBytes(), 0, splitPoint.getLength()));
+      } finally {
+        ThriftUtil.returnClient(client);
+      }
+    }
+    
+    public void flushTablet(ZooLock lock, KeyExtent extent) throws TException {
+      TabletClientService.Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), address, conf);
+      try {
+        client.flushTablet(Tracer.traceInfo(), SystemCredentials.get().toThrift(instance), lockString(lock), extent.toThrift());
+      } finally {
+        ThriftUtil.returnClient(client);
+      }
+    }
+    
+    public void compact(ZooLock lock, String tableId, byte[] startRow, byte[] endRow) throws TException {
+      TabletClientService.Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), address, conf);
+      try {
+        client.compact(Tracer.traceInfo(), SystemCredentials.get().toThrift(instance), lockString(lock), tableId,
+            startRow == null ? null : ByteBuffer.wrap(startRow), endRow == null ? null : ByteBuffer.wrap(endRow));
+      } finally {
+        ThriftUtil.returnClient(client);
+      }
+    }
+    
+    public boolean isActive(long tid) throws TException {
+      TabletClientService.Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), address, conf);
+      try {
+        return client.isActive(Tracer.traceInfo(), tid);
+      } finally {
+        ThriftUtil.returnClient(client);
+      }
+    }
+    
+  }
+  
+  static class TServerInfo {
+    TServerConnection connection;
+    TServerInstance instance;
+    
+    TServerInfo(TServerInstance instance, TServerConnection connection) {
+      this.connection = connection;
+      this.instance = instance;
+    }
+  };
+  
+  // The set of active tservers with locks, indexed by their name in zookeeper
+  private Map<String,TServerInfo> current = new HashMap<String,TServerInfo>();
+  // as above, indexed by TServerInstance
+  private Map<TServerInstance,TServerInfo> currentInstances = new HashMap<TServerInstance,TServerInfo>();
+  
+  // The set of entries in zookeeper without locks, and the first time each was noticed
+  private Map<String,Long> locklessServers = new HashMap<String,Long>();
+  
+  public LiveTServerSet(Instance instance, AccumuloConfiguration conf, Listener cback) {
+    this.cback = cback;
+    this.instance = instance;
+    this.conf = conf;
+    
+  }
+  
+  public synchronized ZooCache getZooCache() {
+    if (zooCache == null)
+      zooCache = new ZooCache(this);
+    return zooCache;
+  }
+  
+  public synchronized void startListeningForTabletServerChanges() {
+    scanServers();
+    SimpleTimer.getInstance().schedule(new Runnable() {
+      @Override
+      public void run() {
+        scanServers();
+      }
+    }, 0, 5000);
+  }
+  
+  public synchronized void scanServers() {
+    try {
+      final Set<TServerInstance> updates = new HashSet<TServerInstance>();
+      final Set<TServerInstance> doomed = new HashSet<TServerInstance>();
+      
+      final String path = ZooUtil.getRoot(instance) + Constants.ZTSERVERS;
+      
+      HashSet<String> all = new HashSet<String>(current.keySet());
+      all.addAll(getZooCache().getChildren(path));
+      
+      locklessServers.keySet().retainAll(all);
+      
+      for (String zPath : all) {
+        checkServer(updates, doomed, path, zPath);
+      }
+      
+      // log.debug("Current: " + current.keySet());
+      if (!doomed.isEmpty() || !updates.isEmpty())
+        this.cback.update(this, doomed, updates);
+    } catch (Exception ex) {
+      log.error(ex, ex);
+    }
+  }
+  
+  private void deleteServerNode(String serverNode) throws InterruptedException, KeeperException {
+    try {
+      ZooReaderWriter.getInstance().delete(serverNode, -1);
+    } catch (NotEmptyException ex) {
+      // race condition: tserver created the lock after our last check; we'll see it at the next check
+    } catch (NoNodeException nne) {
+      // someone else deleted it
+    }
+  }
+  
+  private synchronized void checkServer(final Set<TServerInstance> updates, final Set<TServerInstance> doomed, final String path, final String zPath)
+      throws TException, InterruptedException, KeeperException {
+    
+    TServerInfo info = current.get(zPath);
+    
+    final String lockPath = path + "/" + zPath;
+    Stat stat = new Stat();
+    byte[] lockData = ZooLock.getLockData(getZooCache(), lockPath, stat);
+    
+    if (lockData == null) {
+      if (info != null) {
+        doomed.add(info.instance);
+        current.remove(zPath);
+        currentInstances.remove(info.instance);
+      }
+      
+      Long firstSeen = locklessServers.get(zPath);
+      if (firstSeen == null) {
+        locklessServers.put(zPath, System.currentTimeMillis());
+      } else if (System.currentTimeMillis() - firstSeen > 10 * 60 * 1000) {
+        deleteServerNode(path + "/" + zPath);
+        locklessServers.remove(zPath);
+      }
+    } else {
+      locklessServers.remove(zPath);
+      ServerServices services = new ServerServices(new String(lockData));
+      HostAndPort client = services.getAddress(ServerServices.Service.TSERV_CLIENT);
+      TServerInstance instance = new TServerInstance(client, stat.getEphemeralOwner());
+      
+      if (info == null) {
+        updates.add(instance);
+        TServerInfo tServerInfo = new TServerInfo(instance, new TServerConnection(client));
+        current.put(zPath, tServerInfo);
+        currentInstances.put(instance, tServerInfo);
+      } else if (!info.instance.equals(instance)) {
+        doomed.add(info.instance);
+        updates.add(instance);
+        TServerInfo tServerInfo = new TServerInfo(instance, new TServerConnection(client));
+        current.put(zPath, tServerInfo);
+        currentInstances.put(info.instance, tServerInfo);
+      }
+    }
+  }
+  
+  @Override
+  public void process(WatchedEvent event) {
+    
+    // its important that these event are propagated by ZooCache, because this ensures when reading zoocache that is has already processed the event and cleared
+    // relevant nodes before code below reads from zoocache
+    
+    if (event.getPath() != null) {
+      if (event.getPath().endsWith(Constants.ZTSERVERS)) {
+        scanServers();
+      } else if (event.getPath().contains(Constants.ZTSERVERS)) {
+        int pos = event.getPath().lastIndexOf('/');
+        
+        // do only if ZTSERVER is parent
+        if (pos >= 0 && event.getPath().substring(0, pos).endsWith(Constants.ZTSERVERS)) {
+          
+          String server = event.getPath().substring(pos + 1);
+          
+          final Set<TServerInstance> updates = new HashSet<TServerInstance>();
+          final Set<TServerInstance> doomed = new HashSet<TServerInstance>();
+          
+          final String path = ZooUtil.getRoot(instance) + Constants.ZTSERVERS;
+          
+          try {
+            checkServer(updates, doomed, path, server);
+            if (!doomed.isEmpty() || !updates.isEmpty())
+              this.cback.update(this, doomed, updates);
+          } catch (Exception ex) {
+            log.error(ex, ex);
+          }
+        }
+      }
+    }
+  }
+  
+  public synchronized TServerConnection getConnection(TServerInstance server) throws TException {
+    if (server == null)
+      return null;
+    TServerInfo tServerInfo = currentInstances.get(server);
+    if (tServerInfo == null)
+      return null;
+    return tServerInfo.connection;
+  }
+  
+  public synchronized Set<TServerInstance> getCurrentServers() {
+    return new HashSet<TServerInstance>(currentInstances.keySet());
+  }
+  
+  public synchronized int size() {
+    return current.size();
+  }
+  
+  public synchronized TServerInstance find(String tabletServer) {
+    HostAndPort addr = AddressUtil.parseAddress(tabletServer);
+    for (Entry<String,TServerInfo> entry : current.entrySet()) {
+      if (entry.getValue().instance.getLocation().equals(addr))
+        return entry.getValue().instance;
+    }
+    return null;
+  }
+  
+  public synchronized void remove(TServerInstance server) {
+    String zPath = null;
+    for (Entry<String,TServerInfo> entry : current.entrySet()) {
+      if (entry.getValue().instance.equals(server)) {
+        zPath = entry.getKey();
+        break;
+      }
+    }
+    if (zPath == null)
+      return;
+    current.remove(zPath);
+    currentInstances.remove(server);
+    
+    log.info("Removing zookeeper lock for " + server);
+    String fullpath = ZooUtil.getRoot(instance) + Constants.ZTSERVERS + "/" + zPath;
+    try {
+      ZooReaderWriter.getRetryingInstance().recursiveDelete(fullpath, SKIP);
+    } catch (Exception e) {
+      String msg = "error removing tablet server lock";
+      log.fatal(msg, e);
+      Halt.halt(msg, -1);
+    }
+    getZooCache().clear(fullpath);
+  }
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/balancer/ChaoticLoadBalancer.java
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diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/balancer/ChaoticLoadBalancer.java b/server/base/src/main/java/org/apache/accumulo/server/master/balancer/ChaoticLoadBalancer.java
new file mode 100644
index 0000000..ec3371c
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/balancer/ChaoticLoadBalancer.java
@@ -0,0 +1,143 @@
+/*
+ * 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.accumulo.server.master.balancer;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Random;
+import java.util.Set;
+import java.util.SortedMap;
+
+import org.apache.accumulo.core.client.impl.thrift.ThriftSecurityException;
+import org.apache.accumulo.core.data.KeyExtent;
+import org.apache.accumulo.core.master.thrift.TableInfo;
+import org.apache.accumulo.core.master.thrift.TabletServerStatus;
+import org.apache.accumulo.core.metadata.MetadataTable;
+import org.apache.accumulo.core.tabletserver.thrift.TabletStats;
+import org.apache.accumulo.server.conf.ServerConfiguration;
+import org.apache.accumulo.server.master.state.TServerInstance;
+import org.apache.accumulo.server.master.state.TabletMigration;
+import org.apache.thrift.TException;
+
+/**
+ * A chaotic load balancer used for testing. It constantly shuffles tablets, preventing them from resting in a single location for very long. This is not
+ * designed for performance, do not use on production systems. I'm calling it the LokiLoadBalancer.
+ */
+public class ChaoticLoadBalancer extends TabletBalancer {
+  Random r = new Random();
+  
+  @Override
+  public void getAssignments(SortedMap<TServerInstance,TabletServerStatus> current, Map<KeyExtent,TServerInstance> unassigned,
+      Map<KeyExtent,TServerInstance> assignments) {
+    long total = assignments.size() + unassigned.size();
+    long avg = (long) Math.ceil(((double) total) / current.size());
+    Map<TServerInstance,Long> toAssign = new HashMap<TServerInstance,Long>();
+    List<TServerInstance> tServerArray = new ArrayList<TServerInstance>();
+    for (Entry<TServerInstance,TabletServerStatus> e : current.entrySet()) {
+      long numTablets = 0;
+      for (TableInfo ti : e.getValue().getTableMap().values()) {
+        numTablets += ti.tablets;
+      }
+      if (numTablets < avg) {
+        tServerArray.add(e.getKey());
+        toAssign.put(e.getKey(), avg - numTablets);
+      }
+    }
+    
+    for (KeyExtent ke : unassigned.keySet()) {
+      int index = r.nextInt(tServerArray.size());
+      TServerInstance dest = tServerArray.get(index);
+      assignments.put(ke, dest);
+      long remaining = toAssign.get(dest).longValue() - 1;
+      if (remaining == 0) {
+        tServerArray.remove(index);
+        toAssign.remove(dest);
+      } else {
+        toAssign.put(dest, remaining);
+      }
+    }
+  }
+  
+  /**
+   * Will balance randomly, maintaining distribution
+   */
+  @Override
+  public long balance(SortedMap<TServerInstance,TabletServerStatus> current, Set<KeyExtent> migrations, List<TabletMigration> migrationsOut) {
+    Map<TServerInstance,Long> numTablets = new HashMap<TServerInstance,Long>();
+    List<TServerInstance> underCapacityTServer = new ArrayList<TServerInstance>();
+    
+    if (!migrations.isEmpty())
+      return 100;
+    
+    boolean moveMetadata = r.nextInt(4) == 0;
+    long totalTablets = 0;
+    for (Entry<TServerInstance,TabletServerStatus> e : current.entrySet()) {
+      long tabletCount = 0;
+      for (TableInfo ti : e.getValue().getTableMap().values()) {
+        tabletCount += ti.tablets;
+      }
+      numTablets.put(e.getKey(), tabletCount);
+      underCapacityTServer.add(e.getKey());
+      totalTablets += tabletCount;
+    }
+    // totalTablets is fuzzy due to asynchronicity of the stats
+    // *1.2 to handle fuzziness, and prevent locking for 'perfect' balancing scenarios
+    long avg = (long) Math.ceil(((double) totalTablets) / current.size() * 1.2);
+    
+    for (Entry<TServerInstance,TabletServerStatus> e : current.entrySet()) {
+      for (String table : e.getValue().getTableMap().keySet()) {
+        if (!moveMetadata && MetadataTable.NAME.equals(table))
+          continue;
+        try {
+          for (TabletStats ts : getOnlineTabletsForTable(e.getKey(), table)) {
+            KeyExtent ke = new KeyExtent(ts.extent);
+            int index = r.nextInt(underCapacityTServer.size());
+            TServerInstance dest = underCapacityTServer.get(index);
+            if (dest.equals(e.getKey()))
+              continue;
+            migrationsOut.add(new TabletMigration(ke, e.getKey(), dest));
+            if (numTablets.put(dest, numTablets.get(dest) + 1) > avg)
+              underCapacityTServer.remove(index);
+            if (numTablets.put(e.getKey(), numTablets.get(e.getKey()) - 1) <= avg && !underCapacityTServer.contains(e.getKey()))
+              underCapacityTServer.add(e.getKey());
+            
+            // We can get some craziness with only 1 tserver, so lets make sure there's always an option!
+            if (underCapacityTServer.isEmpty())
+              underCapacityTServer.addAll(numTablets.keySet());
+          }
+        } catch (ThriftSecurityException e1) {
+          // Shouldn't happen, but carry on if it does
+          e1.printStackTrace();
+        } catch (TException e1) {
+          // Shouldn't happen, but carry on if it does
+          e1.printStackTrace();
+        }
+      }
+    }
+    
+    return 100;
+  }
+  
+  @Override
+  public void init(ServerConfiguration conf) {
+    super.init(conf);
+  }
+  
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/balancer/DefaultLoadBalancer.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/balancer/DefaultLoadBalancer.java b/server/base/src/main/java/org/apache/accumulo/server/master/balancer/DefaultLoadBalancer.java
new file mode 100644
index 0000000..9b88d74
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/balancer/DefaultLoadBalancer.java
@@ -0,0 +1,318 @@
+/*
+ * 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.accumulo.server.master.balancer;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+import java.util.SortedMap;
+
+import org.apache.accumulo.core.data.KeyExtent;
+import org.apache.accumulo.core.master.thrift.TableInfo;
+import org.apache.accumulo.core.master.thrift.TabletServerStatus;
+import org.apache.accumulo.core.tabletserver.thrift.TabletStats;
+import org.apache.accumulo.server.master.state.TServerInstance;
+import org.apache.accumulo.server.master.state.TabletMigration;
+import org.apache.log4j.Logger;
+
+public class DefaultLoadBalancer extends TabletBalancer {
+  
+  private static final Logger log = Logger.getLogger(DefaultLoadBalancer.class);
+  
+  Iterator<TServerInstance> assignments;
+  // if tableToBalance is set, then only balance the given table
+  String tableToBalance = null;
+  
+  public DefaultLoadBalancer() {
+    
+  }
+  
+  public DefaultLoadBalancer(String table) {
+    tableToBalance = table;
+  }
+  
+  List<TServerInstance> randomize(Set<TServerInstance> locations) {
+    List<TServerInstance> result = new ArrayList<TServerInstance>(locations);
+    Collections.shuffle(result);
+    return result;
+  }
+  
+  public TServerInstance getAssignment(SortedMap<TServerInstance,TabletServerStatus> locations, KeyExtent extent, TServerInstance last) {
+    if (locations.size() == 0)
+      return null;
+    
+    if (last != null) {
+      // Maintain locality
+      TServerInstance simple = new TServerInstance(last.getLocation(), "");
+      Iterator<TServerInstance> find = locations.tailMap(simple).keySet().iterator();
+      if (find.hasNext()) {
+        TServerInstance current = find.next();
+        if (current.host().equals(last.host()))
+          return current;
+      }
+    }
+    
+    // The strategy here is to walk through the locations and hand them back, one at a time
+    // Grab an iterator off of the set of options; use a new iterator if it hands back something not in the current list.
+    if (assignments == null || !assignments.hasNext())
+      assignments = randomize(locations.keySet()).iterator();
+    TServerInstance result = assignments.next();
+    if (!locations.containsKey(result)) {
+      assignments = null;
+      return randomize(locations.keySet()).iterator().next();
+    }
+    return result;
+  }
+  
+  static class ServerCounts implements Comparable<ServerCounts> {
+    public final TServerInstance server;
+    public final int count;
+    public final TabletServerStatus status;
+    
+    ServerCounts(int count, TServerInstance server, TabletServerStatus status) {
+      this.count = count;
+      this.server = server;
+      this.status = status;
+    }
+    
+    public int compareTo(ServerCounts obj) {
+      int result = count - obj.count;
+      if (result == 0)
+        return server.compareTo(obj.server);
+      return result;
+    }
+  }
+  
+  public boolean getMigrations(Map<TServerInstance,TabletServerStatus> current, List<TabletMigration> result) {
+    boolean moreBalancingNeeded = false;
+    try {
+      // no moves possible
+      if (current.size() < 2) {
+        return false;
+      }
+      
+      // Sort by total number of online tablets, per server
+      int total = 0;
+      ArrayList<ServerCounts> totals = new ArrayList<ServerCounts>();
+      for (Entry<TServerInstance,TabletServerStatus> entry : current.entrySet()) {
+        int serverTotal = 0;
+        if (entry.getValue() != null && entry.getValue().tableMap != null) {
+          for (Entry<String,TableInfo> e : entry.getValue().tableMap.entrySet()) {
+            /**
+             * The check below was on entry.getKey(), but that resolves to a tabletserver not a tablename. Believe it should be e.getKey() which is a tablename
+             */
+            if (tableToBalance == null || tableToBalance.equals(e.getKey()))
+              serverTotal += e.getValue().onlineTablets;
+          }
+        }
+        totals.add(new ServerCounts(serverTotal, entry.getKey(), entry.getValue()));
+        total += serverTotal;
+      }
+      
+      // order from low to high
+      Collections.sort(totals);
+      Collections.reverse(totals);
+      int even = total / totals.size();
+      int numServersOverEven = total % totals.size();
+      
+      // Move tablets from the servers with too many to the servers with
+      // the fewest but only nominate tablets to move once. This allows us
+      // to fill new servers with tablets from a mostly balanced server
+      // very quickly. However, it may take several balancing passes to move
+      // tablets from one hugely overloaded server to many slightly
+      // under-loaded servers.
+      int end = totals.size() - 1;
+      int movedAlready = 0;
+      for (int tooManyIndex = 0; tooManyIndex < totals.size(); tooManyIndex++) {
+        ServerCounts tooMany = totals.get(tooManyIndex);
+        int goal = even;
+        if (tooManyIndex < numServersOverEven) {
+          goal++;
+        }
+        int needToUnload = tooMany.count - goal;
+        ServerCounts tooLittle = totals.get(end);
+        int needToLoad = goal - tooLittle.count - movedAlready;
+        if (needToUnload < 1 && needToLoad < 1) {
+          break;
+        }
+        if (needToUnload >= needToLoad) {
+          result.addAll(move(tooMany, tooLittle, needToLoad));
+          end--;
+          movedAlready = 0;
+        } else {
+          result.addAll(move(tooMany, tooLittle, needToUnload));
+          movedAlready += needToUnload;
+        }
+        if (needToUnload > needToLoad)
+          moreBalancingNeeded = true;
+      }
+      
+    } finally {
+      log.debug("balance ended with " + result.size() + " migrations");
+    }
+    return moreBalancingNeeded;
+  }
+  
+  static class TableDiff {
+    int diff;
+    String table;
+    
+    public TableDiff(int diff, String table) {
+      this.diff = diff;
+      this.table = table;
+    }
+  };
+  
+  /**
+   * Select a tablet based on differences between table loads; if the loads are even, use the busiest table
+   */
+  List<TabletMigration> move(ServerCounts tooMuch, ServerCounts tooLittle, int count) {
+    
+    List<TabletMigration> result = new ArrayList<TabletMigration>();
+    if (count == 0)
+      return result;
+    
+    Map<String,Map<KeyExtent,TabletStats>> onlineTablets = new HashMap<String,Map<KeyExtent,TabletStats>>();
+    // Copy counts so we can update them as we propose migrations
+    Map<String,Integer> tooMuchMap = tabletCountsPerTable(tooMuch.status);
+    Map<String,Integer> tooLittleMap = tabletCountsPerTable(tooLittle.status);
+    
+    for (int i = 0; i < count; i++) {
+      String table;
+      Integer tooLittleCount;
+      if (tableToBalance == null) {
+        // find a table to migrate
+        // look for an uneven table count
+        int biggestDifference = 0;
+        String biggestDifferenceTable = null;
+        for (Entry<String,Integer> tableEntry : tooMuchMap.entrySet()) {
+          String tableID = tableEntry.getKey();
+          if (tooLittleMap.get(tableID) == null)
+            tooLittleMap.put(tableID, 0);
+          int diff = tableEntry.getValue() - tooLittleMap.get(tableID);
+          if (diff > biggestDifference) {
+            biggestDifference = diff;
+            biggestDifferenceTable = tableID;
+          }
+        }
+        if (biggestDifference < 2) {
+          table = busiest(tooMuch.status.tableMap);
+        } else {
+          table = biggestDifferenceTable;
+        }
+      } else {
+        // just balance the given table
+        table = tableToBalance;
+      }
+      Map<KeyExtent,TabletStats> onlineTabletsForTable = onlineTablets.get(table);
+      try {
+        if (onlineTabletsForTable == null) {
+          onlineTabletsForTable = new HashMap<KeyExtent,TabletStats>();
+          for (TabletStats stat : getOnlineTabletsForTable(tooMuch.server, table))
+            onlineTabletsForTable.put(new KeyExtent(stat.extent), stat);
+          onlineTablets.put(table, onlineTabletsForTable);
+        }
+      } catch (Exception ex) {
+        log.error("Unable to select a tablet to move", ex);
+        return result;
+      }
+      KeyExtent extent = selectTablet(tooMuch.server, onlineTabletsForTable);
+      onlineTabletsForTable.remove(extent);
+      if (extent == null)
+        return result;
+      tooMuchMap.put(table, tooMuchMap.get(table) - 1);
+      /**
+       * If a table grows from 1 tablet then tooLittleMap.get(table) can return a null, since there is only one tabletserver that holds all of the tablets. Here
+       * we check to see if in fact that is the case and if so set the value to 0.
+       */
+      tooLittleCount = tooLittleMap.get(table);
+      if (tooLittleCount == null) {
+        tooLittleCount = 0;
+      }
+      tooLittleMap.put(table, tooLittleCount + 1);
+      
+      result.add(new TabletMigration(extent, tooMuch.server, tooLittle.server));
+    }
+    return result;
+  }
+  
+  static Map<String,Integer> tabletCountsPerTable(TabletServerStatus status) {
+    Map<String,Integer> result = new HashMap<String,Integer>();
+    if (status != null && status.tableMap != null) {
+      Map<String,TableInfo> tableMap = status.tableMap;
+      for (Entry<String,TableInfo> entry : tableMap.entrySet()) {
+        result.put(entry.getKey(), entry.getValue().onlineTablets);
+      }
+    }
+    return result;
+  }
+  
+  static KeyExtent selectTablet(TServerInstance tserver, Map<KeyExtent,TabletStats> extents) {
+    if (extents.size() == 0)
+      return null;
+    KeyExtent mostRecentlySplit = null;
+    long splitTime = 0;
+    for (Entry<KeyExtent,TabletStats> entry : extents.entrySet())
+      if (entry.getValue().splitCreationTime >= splitTime) {
+        splitTime = entry.getValue().splitCreationTime;
+        mostRecentlySplit = entry.getKey();
+      }
+    return mostRecentlySplit;
+  }
+  
+  // define what it means for a tablet to be busy
+  private static String busiest(Map<String,TableInfo> tables) {
+    String result = null;
+    double busiest = Double.NEGATIVE_INFINITY;
+    for (Entry<String,TableInfo> entry : tables.entrySet()) {
+      TableInfo info = entry.getValue();
+      double busy = info.ingestRate + info.queryRate;
+      if (busy > busiest) {
+        busiest = busy;
+        result = entry.getKey();
+      }
+    }
+    return result;
+  }
+  
+  @Override
+  public void getAssignments(SortedMap<TServerInstance,TabletServerStatus> current, Map<KeyExtent,TServerInstance> unassigned,
+      Map<KeyExtent,TServerInstance> assignments) {
+    for (Entry<KeyExtent,TServerInstance> entry : unassigned.entrySet()) {
+      assignments.put(entry.getKey(), getAssignment(current, entry.getKey(), entry.getValue()));
+    }
+  }
+  
+  @Override
+  public long balance(SortedMap<TServerInstance,TabletServerStatus> current, Set<KeyExtent> migrations, List<TabletMigration> migrationsOut) {
+    // do we have any servers?
+    if (current.size() > 0) {
+      // Don't migrate if we have migrations in progress
+      if (migrations.size() == 0) {
+        if (getMigrations(current, migrationsOut))
+          return 1 * 1000;
+      }
+    }
+    return 5 * 1000;
+  }
+  
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/balancer/TableLoadBalancer.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/balancer/TableLoadBalancer.java b/server/base/src/main/java/org/apache/accumulo/server/master/balancer/TableLoadBalancer.java
new file mode 100644
index 0000000..3e0a2bf
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/balancer/TableLoadBalancer.java
@@ -0,0 +1,147 @@
+/*
+ * 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.accumulo.server.master.balancer;
+
+import java.lang.reflect.Constructor;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+import java.util.SortedMap;
+
+import org.apache.accumulo.core.client.AccumuloException;
+import org.apache.accumulo.core.client.AccumuloSecurityException;
+import org.apache.accumulo.core.client.admin.TableOperations;
+import org.apache.accumulo.core.conf.Property;
+import org.apache.accumulo.core.data.KeyExtent;
+import org.apache.accumulo.core.master.thrift.TabletServerStatus;
+import org.apache.accumulo.server.master.state.TServerInstance;
+import org.apache.accumulo.server.master.state.TabletMigration;
+import org.apache.accumulo.server.security.SystemCredentials;
+import org.apache.accumulo.start.classloader.vfs.AccumuloVFSClassLoader;
+import org.apache.log4j.Logger;
+
+public class TableLoadBalancer extends TabletBalancer {
+  
+  private static final Logger log = Logger.getLogger(TableLoadBalancer.class);
+  
+  Map<String,TabletBalancer> perTableBalancers = new HashMap<String,TabletBalancer>();
+  
+  private TabletBalancer constructNewBalancerForTable(String clazzName, String table) throws Exception {
+    Class<? extends TabletBalancer> clazz = AccumuloVFSClassLoader.loadClass(clazzName, TabletBalancer.class);
+    Constructor<? extends TabletBalancer> constructor = clazz.getConstructor(String.class);
+    return constructor.newInstance(table);
+  }
+  
+  protected String getLoadBalancerClassNameForTable(String table) {
+    return configuration.getTableConfiguration(table).get(Property.TABLE_LOAD_BALANCER);
+  }
+  
+  protected TabletBalancer getBalancerForTable(String table) {
+    TabletBalancer balancer = perTableBalancers.get(table);
+    
+    String clazzName = getLoadBalancerClassNameForTable(table);
+    
+    if (clazzName == null)
+      clazzName = DefaultLoadBalancer.class.getName();
+    if (balancer != null) {
+      if (clazzName.equals(balancer.getClass().getName()) == false) {
+        // the balancer class for this table does not match the class specified in the configuration
+        try {
+          // attempt to construct a balancer with the specified class
+          TabletBalancer newBalancer = constructNewBalancerForTable(clazzName, table);
+          if (newBalancer != null) {
+            balancer = newBalancer;
+            perTableBalancers.put(table, balancer);
+            balancer.init(configuration);
+          }
+        } catch (Exception e) {
+          log.warn("Failed to load table balancer class " + clazzName + " for table " + table, e);
+        }
+      }
+    }
+    if (balancer == null) {
+      try {
+        balancer = constructNewBalancerForTable(clazzName, table);
+        log.info("Loaded class " + clazzName + " for table " + table);
+      } catch (Exception e) {
+        log.warn("Failed to load table balancer class " + clazzName + " for table " + table, e);
+      }
+      
+      if (balancer == null) {
+        log.info("Using balancer " + DefaultLoadBalancer.class.getName() + " for table " + table);
+        balancer = new DefaultLoadBalancer(table);
+      }
+      perTableBalancers.put(table, balancer);
+      balancer.init(configuration);
+    }
+    return balancer;
+  }
+  
+  @Override
+  public void getAssignments(SortedMap<TServerInstance,TabletServerStatus> current, Map<KeyExtent,TServerInstance> unassigned,
+      Map<KeyExtent,TServerInstance> assignments) {
+    // separate the unassigned into tables
+    Map<String,Map<KeyExtent,TServerInstance>> groupedUnassigned = new HashMap<String,Map<KeyExtent,TServerInstance>>();
+    for (Entry<KeyExtent,TServerInstance> e : unassigned.entrySet()) {
+      Map<KeyExtent,TServerInstance> tableUnassigned = groupedUnassigned.get(e.getKey().getTableId().toString());
+      if (tableUnassigned == null) {
+        tableUnassigned = new HashMap<KeyExtent,TServerInstance>();
+        groupedUnassigned.put(e.getKey().getTableId().toString(), tableUnassigned);
+      }
+      tableUnassigned.put(e.getKey(), e.getValue());
+    }
+    for (Entry<String,Map<KeyExtent,TServerInstance>> e : groupedUnassigned.entrySet()) {
+      Map<KeyExtent,TServerInstance> newAssignments = new HashMap<KeyExtent,TServerInstance>();
+      getBalancerForTable(e.getKey()).getAssignments(current, e.getValue(), newAssignments);
+      assignments.putAll(newAssignments);
+    }
+  }
+  
+  private TableOperations tops = null;
+  
+  protected TableOperations getTableOperations() {
+    if (tops == null)
+      try {
+        tops = configuration.getInstance().getConnector(SystemCredentials.get().getPrincipal(), SystemCredentials.get().getToken()).tableOperations();
+      } catch (AccumuloException e) {
+        log.error("Unable to access table operations from within table balancer", e);
+      } catch (AccumuloSecurityException e) {
+        log.error("Unable to access table operations from within table balancer", e);
+      }
+    return tops;
+  }
+  
+  @Override
+  public long balance(SortedMap<TServerInstance,TabletServerStatus> current, Set<KeyExtent> migrations, List<TabletMigration> migrationsOut) {
+    long minBalanceTime = 5 * 1000;
+    // Iterate over the tables and balance each of them
+    TableOperations t = getTableOperations();
+    if (t == null)
+      return minBalanceTime;
+    for (String s : t.tableIdMap().values()) {
+      ArrayList<TabletMigration> newMigrations = new ArrayList<TabletMigration>();
+      long tableBalanceTime = getBalancerForTable(s).balance(current, migrations, newMigrations);
+      if (tableBalanceTime < minBalanceTime)
+        minBalanceTime = tableBalanceTime;
+      migrationsOut.addAll(newMigrations);
+    }
+    return minBalanceTime;
+  }
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/balancer/TabletBalancer.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/balancer/TabletBalancer.java b/server/base/src/main/java/org/apache/accumulo/server/master/balancer/TabletBalancer.java
new file mode 100644
index 0000000..fd76ce2
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/balancer/TabletBalancer.java
@@ -0,0 +1,151 @@
+/*
+ * 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.accumulo.server.master.balancer;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.SortedMap;
+
+import org.apache.accumulo.core.client.impl.thrift.ThriftSecurityException;
+import org.apache.accumulo.core.data.KeyExtent;
+import org.apache.accumulo.core.master.thrift.TabletServerStatus;
+import org.apache.accumulo.core.tabletserver.thrift.TabletClientService;
+import org.apache.accumulo.core.tabletserver.thrift.TabletClientService.Client;
+import org.apache.accumulo.core.tabletserver.thrift.TabletStats;
+import org.apache.accumulo.core.util.ThriftUtil;
+import org.apache.accumulo.server.conf.ServerConfiguration;
+import org.apache.accumulo.server.master.state.TServerInstance;
+import org.apache.accumulo.server.master.state.TabletMigration;
+import org.apache.accumulo.server.security.SystemCredentials;
+import org.apache.accumulo.trace.instrument.Tracer;
+import org.apache.log4j.Logger;
+import org.apache.thrift.TException;
+import org.apache.thrift.transport.TTransportException;
+
+public abstract class TabletBalancer {
+  
+  private static final Logger log = Logger.getLogger(TabletBalancer.class);
+  
+  protected ServerConfiguration configuration;
+  
+  /**
+   * Initialize the TabletBalancer. This gives the balancer the opportunity to read the configuration.
+   */
+  public void init(ServerConfiguration conf) {
+    configuration = conf;
+  }
+  
+  /**
+   * Assign tablets to tablet servers. This method is called whenever the master finds tablets that are unassigned.
+   * 
+   * @param current
+   *          The current table-summary state of all the online tablet servers. Read-only. The TabletServerStatus for each server may be null if the tablet
+   *          server has not yet responded to a recent request for status.
+   * @param unassigned
+   *          A map from unassigned tablet to the last known tablet server. Read-only.
+   * @param assignments
+   *          A map from tablet to assigned server. Write-only.
+   */
+  abstract public void getAssignments(SortedMap<TServerInstance,TabletServerStatus> current, Map<KeyExtent,TServerInstance> unassigned,
+      Map<KeyExtent,TServerInstance> assignments);
+  
+  /**
+   * Ask the balancer if any migrations are necessary.
+   * 
+   * @param current
+   *          The current table-summary state of all the online tablet servers. Read-only.
+   * @param migrations
+   *          the current set of migrations. Read-only.
+   * @param migrationsOut
+   *          new migrations to perform; should not contain tablets in the current set of migrations. Write-only.
+   * @return the time, in milliseconds, to wait before re-balancing.
+   * 
+   *         This method will not be called when there are unassigned tablets.
+   */
+  public abstract long balance(SortedMap<TServerInstance,TabletServerStatus> current, Set<KeyExtent> migrations, List<TabletMigration> migrationsOut);
+  
+  /**
+   * Fetch the tablets for the given table by asking the tablet server. Useful if your balance strategy needs details at the tablet level to decide what tablets
+   * to move.
+   * 
+   * @param tserver
+   *          The tablet server to ask.
+   * @param tableId
+   *          The table id
+   * @return a list of tablet statistics
+   * @throws ThriftSecurityException
+   *           tablet server disapproves of your internal System password.
+   * @throws TException
+   *           any other problem
+   */
+  public List<TabletStats> getOnlineTabletsForTable(TServerInstance tserver, String tableId) throws ThriftSecurityException, TException {
+    log.debug("Scanning tablet server " + tserver + " for table " + tableId);
+    Client client = ThriftUtil.getClient(new TabletClientService.Client.Factory(), tserver.getLocation(), configuration.getConfiguration());
+    try {
+      List<TabletStats> onlineTabletsForTable = client.getTabletStats(Tracer.traceInfo(), SystemCredentials.get().toThrift(configuration.getInstance()),
+          tableId);
+      return onlineTabletsForTable;
+    } catch (TTransportException e) {
+      log.error("Unable to connect to " + tserver + ": " + e);
+    } finally {
+      ThriftUtil.returnClient(client);
+    }
+    return null;
+  }
+  
+  /**
+   * Utility to ensure that the migrations from balance() are consistent:
+   * <ul>
+   * <li>Tablet objects are not null
+   * <li>Source and destination tablet servers are not null and current
+   * </ul>
+   * 
+   * @param current
+   * @param migrations
+   * @return A list of TabletMigration object that passed sanity checks.
+   */
+  public static List<TabletMigration> checkMigrationSanity(Set<TServerInstance> current, List<TabletMigration> migrations) {
+    List<TabletMigration> result = new ArrayList<TabletMigration>(migrations.size());
+    for (TabletMigration m : migrations) {
+      if (m.tablet == null) {
+        log.warn("Balancer gave back a null tablet " + m);
+        continue;
+      }
+      if (m.newServer == null) {
+        log.warn("Balancer did not set the destination " + m);
+        continue;
+      }
+      if (m.oldServer == null) {
+        log.warn("Balancer did not set the source " + m);
+        continue;
+      }
+      if (!current.contains(m.oldServer)) {
+        log.warn("Balancer wants to move a tablet from a server that is not current: " + m);
+        continue;
+      }
+      if (!current.contains(m.newServer)) {
+        log.warn("Balancer wants to move a tablet to a server that is not current: " + m);
+        continue;
+      }
+      result.add(m);
+    }
+    return result;
+  }
+  
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/recovery/HadoopLogCloser.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/recovery/HadoopLogCloser.java b/server/base/src/main/java/org/apache/accumulo/server/master/recovery/HadoopLogCloser.java
new file mode 100644
index 0000000..b3c0934
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/recovery/HadoopLogCloser.java
@@ -0,0 +1,61 @@
+/*
+ * 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.accumulo.server.master.recovery;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+
+import org.apache.accumulo.core.conf.AccumuloConfiguration;
+import org.apache.accumulo.core.conf.Property;
+import org.apache.accumulo.server.fs.VolumeManager;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.LocalFileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hdfs.DistributedFileSystem;
+import org.apache.log4j.Logger;
+
+public class HadoopLogCloser implements LogCloser {
+
+  private static Logger log = Logger.getLogger(HadoopLogCloser.class);
+
+  @Override
+  public long close(AccumuloConfiguration conf, VolumeManager fs, Path source) throws IOException {
+    FileSystem ns = fs.getFileSystemByPath(source);
+    if (ns instanceof DistributedFileSystem) {
+      DistributedFileSystem dfs = (DistributedFileSystem) ns;
+      try {
+        if (!dfs.recoverLease(source)) {
+          log.info("Waiting for file to be closed " + source.toString());
+          return conf.getTimeInMillis(Property.MASTER_LEASE_RECOVERY_WAITING_PERIOD);
+        }
+        log.info("Recovered lease on " + source.toString());
+      } catch (FileNotFoundException ex) {
+        throw ex;
+      } catch (Exception ex) {
+        log.warn("Error recovering lease on " + source.toString(), ex);
+        ns.append(source).close();
+        log.info("Recovered lease on " + source.toString() + " using append");
+      }
+    } else if (ns instanceof LocalFileSystem) {
+      // ignore
+    } else {
+      throw new IllegalStateException("Don't know how to recover a lease for " + fs.getClass().getName());
+    }
+    return 0;
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/recovery/LogCloser.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/recovery/LogCloser.java b/server/base/src/main/java/org/apache/accumulo/server/master/recovery/LogCloser.java
new file mode 100644
index 0000000..deeea61
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/recovery/LogCloser.java
@@ -0,0 +1,27 @@
+/*
+ * 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.accumulo.server.master.recovery;
+
+import java.io.IOException;
+
+import org.apache.accumulo.core.conf.AccumuloConfiguration;
+import org.apache.accumulo.server.fs.VolumeManager;
+import org.apache.hadoop.fs.Path;
+
+public interface LogCloser {
+  public long close(AccumuloConfiguration conf, VolumeManager fs, Path path) throws IOException;
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/recovery/MapRLogCloser.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/recovery/MapRLogCloser.java b/server/base/src/main/java/org/apache/accumulo/server/master/recovery/MapRLogCloser.java
new file mode 100644
index 0000000..bba7ac5
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/recovery/MapRLogCloser.java
@@ -0,0 +1,47 @@
+/*
+ * 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.accumulo.server.master.recovery;
+
+import java.io.IOException;
+
+import org.apache.accumulo.core.conf.AccumuloConfiguration;
+import org.apache.accumulo.server.fs.VolumeManager;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.permission.FsPermission;
+import org.apache.log4j.Logger;
+
+public class MapRLogCloser implements LogCloser {
+
+  private static Logger log = Logger.getLogger(MapRLogCloser.class);
+
+  @Override
+  public long close(AccumuloConfiguration conf, VolumeManager fs, Path path) throws IOException {
+    log.info("Recovering file " + path.toString() + " by changing permission to readonly");
+    FileSystem ns = fs.getFileSystemByPath(path);
+    FsPermission roPerm = new FsPermission((short) 0444);
+    try {
+      ns.setPermission(path, roPerm);
+      return 0;
+    } catch (IOException ex) {
+      log.error("error recovering lease ", ex);
+      // lets do this again
+      return 1000;
+    }
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/state/Assignment.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/state/Assignment.java b/server/base/src/main/java/org/apache/accumulo/server/master/state/Assignment.java
new file mode 100644
index 0000000..b2510fc
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/state/Assignment.java
@@ -0,0 +1,30 @@
+/*
+ * 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.accumulo.server.master.state;
+
+import org.apache.accumulo.core.data.KeyExtent;
+import org.apache.accumulo.server.master.state.TServerInstance;
+
+public class Assignment {
+  public KeyExtent tablet;
+  public TServerInstance server;
+  
+  public Assignment(KeyExtent tablet, TServerInstance server) {
+    this.tablet = tablet;
+    this.server = server;
+  }
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/state/CurrentState.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/state/CurrentState.java b/server/base/src/main/java/org/apache/accumulo/server/master/state/CurrentState.java
new file mode 100644
index 0000000..f4d98bf
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/state/CurrentState.java
@@ -0,0 +1,30 @@
+/*
+ * 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.accumulo.server.master.state;
+
+import java.util.Collection;
+import java.util.Set;
+
+public interface CurrentState {
+  
+  Set<String> onlineTables();
+  
+  Set<TServerInstance> onlineTabletServers();
+  
+  Collection<MergeInfo> merges();
+  
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/state/DeadServerList.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/state/DeadServerList.java b/server/base/src/main/java/org/apache/accumulo/server/master/state/DeadServerList.java
new file mode 100644
index 0000000..b2ea7d6
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/state/DeadServerList.java
@@ -0,0 +1,80 @@
+/*
+ * 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.accumulo.server.master.state;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.accumulo.core.master.thrift.DeadServer;
+import org.apache.accumulo.fate.zookeeper.IZooReaderWriter;
+import org.apache.accumulo.fate.zookeeper.ZooUtil.NodeExistsPolicy;
+import org.apache.accumulo.fate.zookeeper.ZooUtil.NodeMissingPolicy;
+import org.apache.accumulo.server.zookeeper.ZooReaderWriter;
+import org.apache.log4j.Logger;
+import org.apache.zookeeper.data.Stat;
+
+public class DeadServerList {
+  private static final Logger log = Logger.getLogger(DeadServerList.class);
+  private final String path;
+  
+  public DeadServerList(String path) {
+    this.path = path;
+    IZooReaderWriter zoo = ZooReaderWriter.getInstance();
+    try {
+      zoo.mkdirs(path);
+    } catch (Exception ex) {
+      log.error("Unable to make parent directories of " + path, ex);
+    }
+  }
+  
+  public List<DeadServer> getList() {
+    List<DeadServer> result = new ArrayList<DeadServer>();
+    IZooReaderWriter zoo = ZooReaderWriter.getInstance();
+    try {
+      List<String> children = zoo.getChildren(path);
+      if (children != null) {
+        for (String child : children) {
+          Stat stat = new Stat();
+          byte[] data = zoo.getData(path + "/" + child, stat);
+          DeadServer server = new DeadServer(child, stat.getMtime(), new String(data));
+          result.add(server);
+        }
+      }
+    } catch (Exception ex) {
+      log.error(ex, ex);
+    }
+    return result;
+  }
+  
+  public void delete(String server) {
+    IZooReaderWriter zoo = ZooReaderWriter.getInstance();
+    try {
+      zoo.recursiveDelete(path + "/" + server, NodeMissingPolicy.SKIP);
+    } catch (Exception ex) {
+      log.error(ex, ex);
+    }
+  }
+  
+  public void post(String server, String cause) {
+    IZooReaderWriter zoo = ZooReaderWriter.getInstance();
+    try {
+      zoo.putPersistentData(path + "/" + server, cause.getBytes(), NodeExistsPolicy.SKIP);
+    } catch (Exception ex) {
+      log.error(ex, ex);
+    }
+  }
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/state/DistributedStore.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/state/DistributedStore.java b/server/base/src/main/java/org/apache/accumulo/server/master/state/DistributedStore.java
new file mode 100644
index 0000000..ad658df
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/state/DistributedStore.java
@@ -0,0 +1,34 @@
+/*
+ * 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.accumulo.server.master.state;
+
+import java.util.List;
+
+/*
+ * An abstract version of ZooKeeper that we can write tests against.
+ */
+public interface DistributedStore {
+  
+  public List<String> getChildren(String path) throws DistributedStoreException;
+  
+  public byte[] get(String path) throws DistributedStoreException;
+  
+  public void put(String path, byte[] bs) throws DistributedStoreException;
+  
+  public void remove(String path) throws DistributedStoreException;
+  
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/state/DistributedStoreException.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/state/DistributedStoreException.java b/server/base/src/main/java/org/apache/accumulo/server/master/state/DistributedStoreException.java
new file mode 100644
index 0000000..3d3a725
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/state/DistributedStoreException.java
@@ -0,0 +1,34 @@
+/*
+ * 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.accumulo.server.master.state;
+
+public class DistributedStoreException extends Exception {
+  
+  private static final long serialVersionUID = 1L;
+  
+  public DistributedStoreException(String why) {
+    super(why);
+  }
+  
+  public DistributedStoreException(Exception cause) {
+    super(cause);
+  }
+  
+  public DistributedStoreException(String why, Exception cause) {
+    super(why, cause);
+  }
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/state/MergeInfo.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/state/MergeInfo.java b/server/base/src/main/java/org/apache/accumulo/server/master/state/MergeInfo.java
new file mode 100644
index 0000000..708b1b7
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/state/MergeInfo.java
@@ -0,0 +1,107 @@
+/*
+ * 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.accumulo.server.master.state;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+
+import org.apache.accumulo.core.data.KeyExtent;
+import org.apache.hadoop.io.Writable;
+
+/**
+ * Information about the current merge/rangeDelete.
+ * 
+ * Writable to serialize for zookeeper and the Tablet
+ */
+public class MergeInfo implements Writable {
+  
+  public enum Operation {
+    MERGE, DELETE,
+  }
+  
+  MergeState state = MergeState.NONE;
+  KeyExtent extent;
+  Operation operation = Operation.MERGE;
+  
+  public MergeInfo() {}
+  
+  @Override
+  public void readFields(DataInput in) throws IOException {
+    extent = new KeyExtent();
+    extent.readFields(in);
+    state = MergeState.values()[in.readInt()];
+    operation = Operation.values()[in.readInt()];
+  }
+  
+  @Override
+  public void write(DataOutput out) throws IOException {
+    extent.write(out);
+    out.writeInt(state.ordinal());
+    out.writeInt(operation.ordinal());
+  }
+  
+  public MergeInfo(KeyExtent range, Operation op) {
+    this.extent = range;
+    this.operation = op;
+  }
+  
+  public MergeState getState() {
+    return state;
+  }
+  
+  public KeyExtent getExtent() {
+    return extent;
+  }
+  
+  public Operation getOperation() {
+    return operation;
+  }
+  
+  public void setState(MergeState state) {
+    this.state = state;
+  }
+  
+  public boolean isDelete() {
+    return this.operation.equals(Operation.DELETE);
+  }
+  
+  public boolean needsToBeChopped(KeyExtent otherExtent) {
+    // During a delete, the block after the merge will be stretched to cover the deleted area.
+    // Therefore, it needs to be chopped
+    if (!otherExtent.getTableId().equals(extent.getTableId()))
+      return false;
+    if (isDelete())
+      return otherExtent.getPrevEndRow() != null && otherExtent.getPrevEndRow().equals(extent.getEndRow());
+    else
+      return this.extent.overlaps(otherExtent);
+  }
+  
+  public boolean overlaps(KeyExtent otherExtent) {
+    boolean result = this.extent.overlaps(otherExtent);
+    if (!result && needsToBeChopped(otherExtent))
+      return true;
+    return result;
+  }
+  
+  @Override
+  public String toString() {
+    if (!state.equals(MergeState.NONE))
+      return "Merge " + operation.toString() + " of " + extent + " State: " + state;
+    return "No Merge in progress";
+  }
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/state/MergeState.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/state/MergeState.java b/server/base/src/main/java/org/apache/accumulo/server/master/state/MergeState.java
new file mode 100644
index 0000000..29b6ae3
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/state/MergeState.java
@@ -0,0 +1,49 @@
+/*
+ * 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.accumulo.server.master.state;
+
+public enum MergeState {
+  /**
+   * Not merging
+   */
+  NONE,
+  /**
+   * created, stored in zookeeper, other merges are prevented on the table
+   */
+  STARTED,
+  /**
+   * put all matching tablets online, split tablets if we are deleting
+   */
+  SPLITTING,
+  /**
+   * after the tablet server chops the file, it marks the metadata table with a chopped marker
+   */
+  WAITING_FOR_CHOPPED,
+  /**
+   * when the number of chopped tablets in the range matches the number of online tablets in the range, take the tablets offline
+   */
+  WAITING_FOR_OFFLINE,
+  /**
+   * when the number of chopped, offline tablets equals the number of merge tablets, begin the metadata updates
+   */
+  MERGING,
+  /**
+   * merge is complete, the resulting tablet can be brought online, remove the marker in zookeeper
+   */
+  COMPLETE;
+  
+}

http://git-wip-us.apache.org/repos/asf/accumulo/blob/598821cd/server/base/src/main/java/org/apache/accumulo/server/master/state/MetaDataStateStore.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/master/state/MetaDataStateStore.java b/server/base/src/main/java/org/apache/accumulo/server/master/state/MetaDataStateStore.java
new file mode 100644
index 0000000..082f2ca
--- /dev/null
+++ b/server/base/src/main/java/org/apache/accumulo/server/master/state/MetaDataStateStore.java
@@ -0,0 +1,160 @@
+/*
+ * 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.accumulo.server.master.state;
+
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.accumulo.core.client.BatchWriter;
+import org.apache.accumulo.core.client.BatchWriterConfig;
+import org.apache.accumulo.core.client.Instance;
+import org.apache.accumulo.core.client.MutationsRejectedException;
+import org.apache.accumulo.core.client.TableNotFoundException;
+import org.apache.accumulo.core.data.Mutation;
+import org.apache.accumulo.core.metadata.MetadataTable;
+import org.apache.accumulo.core.metadata.schema.MetadataSchema;
+import org.apache.accumulo.core.metadata.schema.MetadataSchema.TabletsSection;
+import org.apache.accumulo.core.security.Credentials;
+import org.apache.accumulo.server.client.HdfsZooInstance;
+import org.apache.accumulo.server.master.state.CurrentState;
+import org.apache.accumulo.server.master.state.MetaDataTableScanner;
+import org.apache.accumulo.server.master.state.TabletLocationState;
+import org.apache.accumulo.server.security.SystemCredentials;
+import org.apache.hadoop.io.Text;
+
+public class MetaDataStateStore extends TabletStateStore {
+  // private static final Logger log = Logger.getLogger(MetaDataStateStore.class);
+  
+  private static final int THREADS = 4;
+  private static final int LATENCY = 1000;
+  private static final int MAX_MEMORY = 200 * 1024 * 1024;
+  
+  final protected Instance instance;
+  final protected CurrentState state;
+  final protected Credentials credentials;
+  final private String targetTableName;
+  
+  protected MetaDataStateStore(Instance instance, Credentials credentials, CurrentState state, String targetTableName) {
+    this.instance = instance;
+    this.state = state;
+    this.credentials = credentials;
+    this.targetTableName = targetTableName;
+  }
+  
+  public MetaDataStateStore(Instance instance, Credentials credentials, CurrentState state) {
+    this(instance, credentials, state, MetadataTable.NAME);
+  }
+  
+  protected MetaDataStateStore(String tableName) {
+    this(HdfsZooInstance.getInstance(), SystemCredentials.get(), null, tableName);
+  }
+  
+  public MetaDataStateStore() {
+    this(MetadataTable.NAME);
+  }
+  
+  @Override
+  public Iterator<TabletLocationState> iterator() {
+    return new MetaDataTableScanner(instance, credentials, MetadataSchema.TabletsSection.getRange(), state);
+  }
+  
+  @Override
+  public void setLocations(Collection<Assignment> assignments) throws DistributedStoreException {
+    BatchWriter writer = createBatchWriter();
+    try {
+      for (Assignment assignment : assignments) {
+        Mutation m = new Mutation(assignment.tablet.getMetadataEntry());
+        Text cq = assignment.server.asColumnQualifier();
+        m.put(TabletsSection.CurrentLocationColumnFamily.NAME, cq, assignment.server.asMutationValue());
+        m.putDelete(TabletsSection.FutureLocationColumnFamily.NAME, cq);
+        writer.addMutation(m);
+      }
+    } catch (Exception ex) {
+      throw new DistributedStoreException(ex);
+    } finally {
+      try {
+        writer.close();
+      } catch (MutationsRejectedException e) {
+        throw new DistributedStoreException(e);
+      }
+    }
+  }
+  
+  BatchWriter createBatchWriter() {
+    try {
+      return instance.getConnector(credentials.getPrincipal(), credentials.getToken()).createBatchWriter(targetTableName,
+          new BatchWriterConfig().setMaxMemory(MAX_MEMORY).setMaxLatency(LATENCY, TimeUnit.MILLISECONDS).setMaxWriteThreads(THREADS));
+    } catch (TableNotFoundException e) {
+      // ya, I don't think so
+      throw new RuntimeException(e);
+    } catch (Exception e) {
+      throw new RuntimeException(e);
+    }
+  }
+  
+  @Override
+  public void setFutureLocations(Collection<Assignment> assignments) throws DistributedStoreException {
+    BatchWriter writer = createBatchWriter();
+    try {
+      for (Assignment assignment : assignments) {
+        Mutation m = new Mutation(assignment.tablet.getMetadataEntry());
+        m.put(TabletsSection.FutureLocationColumnFamily.NAME, assignment.server.asColumnQualifier(), assignment.server.asMutationValue());
+        writer.addMutation(m);
+      }
+    } catch (Exception ex) {
+      throw new DistributedStoreException(ex);
+    } finally {
+      try {
+        writer.close();
+      } catch (MutationsRejectedException e) {
+        throw new DistributedStoreException(e);
+      }
+    }
+  }
+  
+  @Override
+  public void unassign(Collection<TabletLocationState> tablets) throws DistributedStoreException {
+    
+    BatchWriter writer = createBatchWriter();
+    try {
+      for (TabletLocationState tls : tablets) {
+        Mutation m = new Mutation(tls.extent.getMetadataEntry());
+        if (tls.current != null) {
+          m.putDelete(TabletsSection.CurrentLocationColumnFamily.NAME, tls.current.asColumnQualifier());
+        }
+        if (tls.future != null) {
+          m.putDelete(TabletsSection.FutureLocationColumnFamily.NAME, tls.future.asColumnQualifier());
+        }
+        writer.addMutation(m);
+      }
+    } catch (Exception ex) {
+      throw new DistributedStoreException(ex);
+    } finally {
+      try {
+        writer.close();
+      } catch (MutationsRejectedException e) {
+        throw new DistributedStoreException(e);
+      }
+    }
+  }
+  
+  @Override
+  public String name() {
+    return "Normal Tablets";
+  }
+}