You are viewing a plain text version of this content. The canonical link for it is here.
Posted to commits@hbase.apache.org by ap...@apache.org on 2017/11/17 21:20:34 UTC

[02/13] hbase git commit: HBASE-19114 Split out o.a.h.h.zookeeper from hbase-server and hbase-client

http://git-wip-us.apache.org/repos/asf/hbase/blob/330b0d05/hbase-zookeeper/src/main/java/org/apache/hadoop/hbase/zookeeper/ZKUtil.java
----------------------------------------------------------------------
diff --git a/hbase-zookeeper/src/main/java/org/apache/hadoop/hbase/zookeeper/ZKUtil.java b/hbase-zookeeper/src/main/java/org/apache/hadoop/hbase/zookeeper/ZKUtil.java
new file mode 100644
index 0000000..d8472a9
--- /dev/null
+++ b/hbase-zookeeper/src/main/java/org/apache/hadoop/hbase/zookeeper/ZKUtil.java
@@ -0,0 +1,2072 @@
+/*
+ *
+ * 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 java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.InetSocketAddress;
+import java.net.Socket;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Deque;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+
+import javax.security.auth.login.AppConfigurationEntry;
+import javax.security.auth.login.AppConfigurationEntry.LoginModuleControlFlag;
+
+import org.apache.commons.lang3.StringUtils;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hbase.AuthUtil;
+import org.apache.hadoop.hbase.HBaseConfiguration;
+import org.apache.hadoop.hbase.HConstants;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.apache.hadoop.hbase.exceptions.DeserializationException;
+import org.apache.hadoop.hbase.security.Superusers;
+import org.apache.hadoop.hbase.shaded.com.google.protobuf.InvalidProtocolBufferException;
+import org.apache.hadoop.hbase.shaded.protobuf.ProtobufUtil;
+import org.apache.hadoop.hbase.shaded.protobuf.generated.ReplicationProtos;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.hadoop.hbase.util.Threads;
+import org.apache.hadoop.hbase.zookeeper.ZKUtil.ZKUtilOp.CreateAndFailSilent;
+import org.apache.hadoop.hbase.zookeeper.ZKUtil.ZKUtilOp.DeleteNodeFailSilent;
+import org.apache.hadoop.hbase.zookeeper.ZKUtil.ZKUtilOp.SetData;
+import org.apache.hadoop.security.SecurityUtil;
+import org.apache.hadoop.security.UserGroupInformation;
+import org.apache.hadoop.security.authentication.util.KerberosUtil;
+import org.apache.zookeeper.AsyncCallback;
+import org.apache.zookeeper.CreateMode;
+import org.apache.zookeeper.KeeperException;
+import org.apache.zookeeper.KeeperException.NoNodeException;
+import org.apache.zookeeper.Op;
+import org.apache.zookeeper.Watcher;
+import org.apache.zookeeper.ZooDefs.Ids;
+import org.apache.zookeeper.ZooDefs.Perms;
+import org.apache.zookeeper.ZooKeeper;
+import org.apache.zookeeper.client.ZooKeeperSaslClient;
+import org.apache.zookeeper.data.ACL;
+import org.apache.zookeeper.data.Id;
+import org.apache.zookeeper.data.Stat;
+import org.apache.zookeeper.proto.CreateRequest;
+import org.apache.zookeeper.proto.DeleteRequest;
+import org.apache.zookeeper.proto.SetDataRequest;
+import org.apache.zookeeper.server.ZooKeeperSaslServer;
+
+/**
+ * Internal HBase utility class for ZooKeeper.
+ *
+ * <p>Contains only static methods and constants.
+ *
+ * <p>Methods all throw {@link KeeperException} if there is an unexpected
+ * zookeeper exception, so callers of these methods must handle appropriately.
+ * If ZK is required for the operation, the server will need to be aborted.
+ */
+@InterfaceAudience.Private
+public class ZKUtil {
+  private static final Log LOG = LogFactory.getLog(ZKUtil.class);
+
+  private static int zkDumpConnectionTimeOut;
+
+  /**
+   * Creates a new connection to ZooKeeper, pulling settings and ensemble config
+   * from the specified configuration object using methods from {@link ZKConfig}.
+   *
+   * Sets the connection status monitoring watcher to the specified watcher.
+   *
+   * @param conf configuration to pull ensemble and other settings from
+   * @param watcher watcher to monitor connection changes
+   * @return connection to zookeeper
+   * @throws IOException if unable to connect to zk or config problem
+   */
+  public static RecoverableZooKeeper connect(Configuration conf, Watcher watcher)
+  throws IOException {
+    String ensemble = ZKConfig.getZKQuorumServersString(conf);
+    return connect(conf, ensemble, watcher);
+  }
+
+  public static RecoverableZooKeeper connect(Configuration conf, String ensemble,
+      Watcher watcher)
+  throws IOException {
+    return connect(conf, ensemble, watcher, null);
+  }
+
+  public static RecoverableZooKeeper connect(Configuration conf, String ensemble,
+      Watcher watcher, final String identifier)
+  throws IOException {
+    if(ensemble == null) {
+      throw new IOException("Unable to determine ZooKeeper ensemble");
+    }
+    int timeout = conf.getInt(HConstants.ZK_SESSION_TIMEOUT,
+        HConstants.DEFAULT_ZK_SESSION_TIMEOUT);
+    if (LOG.isTraceEnabled()) {
+      LOG.trace(identifier + " opening connection to ZooKeeper ensemble=" + ensemble);
+    }
+    int retry = conf.getInt("zookeeper.recovery.retry", 3);
+    int retryIntervalMillis =
+      conf.getInt("zookeeper.recovery.retry.intervalmill", 1000);
+    int maxSleepTime = conf.getInt("zookeeper.recovery.retry.maxsleeptime", 60000);
+    zkDumpConnectionTimeOut = conf.getInt("zookeeper.dump.connection.timeout",
+        1000);
+    return new RecoverableZooKeeper(ensemble, timeout, watcher,
+        retry, retryIntervalMillis, maxSleepTime, identifier);
+  }
+
+  /**
+   * Log in the current zookeeper server process using the given configuration
+   * keys for the credential file and login principal.
+   *
+   * <p><strong>This is only applicable when running on secure hbase</strong>
+   * On regular HBase (without security features), this will safely be ignored.
+   * </p>
+   *
+   * @param conf The configuration data to use
+   * @param keytabFileKey Property key used to configure the path to the credential file
+   * @param userNameKey Property key used to configure the login principal
+   * @param hostname Current hostname to use in any credentials
+   * @throws IOException underlying exception from SecurityUtil.login() call
+   */
+  public static void loginServer(Configuration conf, String keytabFileKey,
+      String userNameKey, String hostname) throws IOException {
+    login(conf, keytabFileKey, userNameKey, hostname,
+          ZooKeeperSaslServer.LOGIN_CONTEXT_NAME_KEY,
+          JaasConfiguration.SERVER_KEYTAB_KERBEROS_CONFIG_NAME);
+  }
+
+  /**
+   * Log in the current zookeeper client using the given configuration
+   * keys for the credential file and login principal.
+   *
+   * <p><strong>This is only applicable when running on secure hbase</strong>
+   * On regular HBase (without security features), this will safely be ignored.
+   * </p>
+   *
+   * @param conf The configuration data to use
+   * @param keytabFileKey Property key used to configure the path to the credential file
+   * @param userNameKey Property key used to configure the login principal
+   * @param hostname Current hostname to use in any credentials
+   * @throws IOException underlying exception from SecurityUtil.login() call
+   */
+  public static void loginClient(Configuration conf, String keytabFileKey,
+      String userNameKey, String hostname) throws IOException {
+    login(conf, keytabFileKey, userNameKey, hostname,
+          ZooKeeperSaslClient.LOGIN_CONTEXT_NAME_KEY,
+          JaasConfiguration.CLIENT_KEYTAB_KERBEROS_CONFIG_NAME);
+  }
+
+  /**
+   * Log in the current process using the given configuration keys for the
+   * credential file and login principal.
+   *
+   * <p><strong>This is only applicable when running on secure hbase</strong>
+   * On regular HBase (without security features), this will safely be ignored.
+   * </p>
+   *
+   * @param conf The configuration data to use
+   * @param keytabFileKey Property key used to configure the path to the credential file
+   * @param userNameKey Property key used to configure the login principal
+   * @param hostname Current hostname to use in any credentials
+   * @param loginContextProperty property name to expose the entry name
+   * @param loginContextName jaas entry name
+   * @throws IOException underlying exception from SecurityUtil.login() call
+   */
+  private static void login(Configuration conf, String keytabFileKey,
+      String userNameKey, String hostname,
+      String loginContextProperty, String loginContextName)
+      throws IOException {
+    if (!isSecureZooKeeper(conf))
+      return;
+
+    // User has specified a jaas.conf, keep this one as the good one.
+    // HBASE_OPTS="-Djava.security.auth.login.config=jaas.conf"
+    if (System.getProperty("java.security.auth.login.config") != null)
+      return;
+
+    // No keytab specified, no auth
+    String keytabFilename = conf.get(keytabFileKey);
+    if (keytabFilename == null) {
+      LOG.warn("no keytab specified for: " + keytabFileKey);
+      return;
+    }
+
+    String principalConfig = conf.get(userNameKey, System.getProperty("user.name"));
+    String principalName = SecurityUtil.getServerPrincipal(principalConfig, hostname);
+
+    // Initialize the "jaas.conf" for keyTab/principal,
+    // If keyTab is not specified use the Ticket Cache.
+    // and set the zookeeper login context name.
+    JaasConfiguration jaasConf = new JaasConfiguration(loginContextName,
+        principalName, keytabFilename);
+    javax.security.auth.login.Configuration.setConfiguration(jaasConf);
+    System.setProperty(loginContextProperty, loginContextName);
+  }
+
+  /**
+   * A JAAS configuration that defines the login modules that we want to use for login.
+   */
+  private static class JaasConfiguration extends javax.security.auth.login.Configuration {
+    private static final String SERVER_KEYTAB_KERBEROS_CONFIG_NAME =
+      "zookeeper-server-keytab-kerberos";
+    private static final String CLIENT_KEYTAB_KERBEROS_CONFIG_NAME =
+      "zookeeper-client-keytab-kerberos";
+
+    private static final Map<String, String> BASIC_JAAS_OPTIONS = new HashMap<>();
+    static {
+      String jaasEnvVar = System.getenv("HBASE_JAAS_DEBUG");
+      if (jaasEnvVar != null && "true".equalsIgnoreCase(jaasEnvVar)) {
+        BASIC_JAAS_OPTIONS.put("debug", "true");
+      }
+    }
+
+    private static final Map<String,String> KEYTAB_KERBEROS_OPTIONS = new HashMap<>();
+    static {
+      KEYTAB_KERBEROS_OPTIONS.put("doNotPrompt", "true");
+      KEYTAB_KERBEROS_OPTIONS.put("storeKey", "true");
+      KEYTAB_KERBEROS_OPTIONS.put("refreshKrb5Config", "true");
+      KEYTAB_KERBEROS_OPTIONS.putAll(BASIC_JAAS_OPTIONS);
+    }
+
+    private static final AppConfigurationEntry KEYTAB_KERBEROS_LOGIN =
+      new AppConfigurationEntry(KerberosUtil.getKrb5LoginModuleName(),
+                                LoginModuleControlFlag.REQUIRED,
+                                KEYTAB_KERBEROS_OPTIONS);
+
+    private static final AppConfigurationEntry[] KEYTAB_KERBEROS_CONF =
+      new AppConfigurationEntry[]{KEYTAB_KERBEROS_LOGIN};
+
+    private javax.security.auth.login.Configuration baseConfig;
+    private final String loginContextName;
+    private final boolean useTicketCache;
+    private final String keytabFile;
+    private final String principal;
+
+    public JaasConfiguration(String loginContextName, String principal, String keytabFile) {
+      this(loginContextName, principal, keytabFile, keytabFile == null || keytabFile.length() == 0);
+    }
+
+    private JaasConfiguration(String loginContextName, String principal,
+                             String keytabFile, boolean useTicketCache) {
+      try {
+        this.baseConfig = javax.security.auth.login.Configuration.getConfiguration();
+      } catch (SecurityException e) {
+        this.baseConfig = null;
+      }
+      this.loginContextName = loginContextName;
+      this.useTicketCache = useTicketCache;
+      this.keytabFile = keytabFile;
+      this.principal = principal;
+      LOG.info("JaasConfiguration loginContextName=" + loginContextName +
+               " principal=" + principal + " useTicketCache=" + useTicketCache +
+               " keytabFile=" + keytabFile);
+    }
+
+    @Override
+    public AppConfigurationEntry[] getAppConfigurationEntry(String appName) {
+      if (loginContextName.equals(appName)) {
+        if (!useTicketCache) {
+          KEYTAB_KERBEROS_OPTIONS.put("keyTab", keytabFile);
+          KEYTAB_KERBEROS_OPTIONS.put("useKeyTab", "true");
+        }
+        KEYTAB_KERBEROS_OPTIONS.put("principal", principal);
+        KEYTAB_KERBEROS_OPTIONS.put("useTicketCache", useTicketCache ? "true" : "false");
+        return KEYTAB_KERBEROS_CONF;
+      }
+      if (baseConfig != null) return baseConfig.getAppConfigurationEntry(appName);
+      return(null);
+    }
+  }
+
+  //
+  // Helper methods
+  //
+  /**
+   * Returns the full path of the immediate parent of the specified node.
+   * @param node path to get parent of
+   * @return parent of path, null if passed the root node or an invalid node
+   */
+  public static String getParent(String node) {
+    int idx = node.lastIndexOf(ZNodePaths.ZNODE_PATH_SEPARATOR);
+    return idx <= 0 ? null : node.substring(0, idx);
+  }
+
+  /**
+   * Get the name of the current node from the specified fully-qualified path.
+   * @param path fully-qualified path
+   * @return name of the current node
+   */
+  public static String getNodeName(String path) {
+    return path.substring(path.lastIndexOf("/")+1);
+  }
+
+  //
+  // Existence checks and watches
+  //
+
+  /**
+   * Watch the specified znode for delete/create/change events.  The watcher is
+   * set whether or not the node exists.  If the node already exists, the method
+   * returns true.  If the node does not exist, the method returns false.
+   *
+   * @param zkw zk reference
+   * @param znode path of node to watch
+   * @return true if znode exists, false if does not exist or error
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static boolean watchAndCheckExists(ZKWatcher zkw, String znode)
+  throws KeeperException {
+    try {
+      Stat s = zkw.getRecoverableZooKeeper().exists(znode, zkw);
+      boolean exists = s != null ? true : false;
+      if (exists) {
+        LOG.debug(zkw.prefix("Set watcher on existing znode=" + znode));
+      } else {
+        LOG.debug(zkw.prefix("Set watcher on znode that does not yet exist, " + znode));
+      }
+      return exists;
+    } catch (KeeperException e) {
+      LOG.warn(zkw.prefix("Unable to set watcher on znode " + znode), e);
+      zkw.keeperException(e);
+      return false;
+    } catch (InterruptedException e) {
+      LOG.warn(zkw.prefix("Unable to set watcher on znode " + znode), e);
+      zkw.interruptedException(e);
+      return false;
+    }
+  }
+
+  /**
+   * Watch the specified znode, but only if exists. Useful when watching
+   * for deletions. Uses .getData() (and handles NoNodeException) instead
+   * of .exists() to accomplish this, as .getData() will only set a watch if
+   * the znode exists.
+   * @param zkw zk reference
+   * @param znode path of node to watch
+   * @return true if the watch is set, false if node does not exists
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static boolean setWatchIfNodeExists(ZKWatcher zkw, String znode)
+      throws KeeperException {
+    try {
+      zkw.getRecoverableZooKeeper().getData(znode, true, null);
+      return true;
+    } catch (NoNodeException e) {
+      return false;
+    } catch (InterruptedException e) {
+      LOG.warn(zkw.prefix("Unable to set watcher on znode " + znode), e);
+      zkw.interruptedException(e);
+      return false;
+    }
+  }
+
+  /**
+   * Check if the specified node exists.  Sets no watches.
+   *
+   * @param zkw zk reference
+   * @param znode path of node to watch
+   * @return version of the node if it exists, -1 if does not exist
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static int checkExists(ZKWatcher zkw, String znode)
+  throws KeeperException {
+    try {
+      Stat s = zkw.getRecoverableZooKeeper().exists(znode, null);
+      return s != null ? s.getVersion() : -1;
+    } catch (KeeperException e) {
+      LOG.warn(zkw.prefix("Unable to set watcher on znode (" + znode + ")"), e);
+      zkw.keeperException(e);
+      return -1;
+    } catch (InterruptedException e) {
+      LOG.warn(zkw.prefix("Unable to set watcher on znode (" + znode + ")"), e);
+      zkw.interruptedException(e);
+      return -1;
+    }
+  }
+
+  //
+  // Znode listings
+  //
+
+  /**
+   * Lists the children znodes of the specified znode.  Also sets a watch on
+   * the specified znode which will capture a NodeDeleted event on the specified
+   * znode as well as NodeChildrenChanged if any children of the specified znode
+   * are created or deleted.
+   *
+   * Returns null if the specified node does not exist.  Otherwise returns a
+   * list of children of the specified node.  If the node exists but it has no
+   * children, an empty list will be returned.
+   *
+   * @param zkw zk reference
+   * @param znode path of node to list and watch children of
+   * @return list of children of the specified node, an empty list if the node
+   *          exists but has no children, and null if the node does not exist
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static List<String> listChildrenAndWatchForNewChildren(
+          ZKWatcher zkw, String znode)
+  throws KeeperException {
+    try {
+      List<String> children = zkw.getRecoverableZooKeeper().getChildren(znode, zkw);
+      return children;
+    } catch(KeeperException.NoNodeException ke) {
+      LOG.debug(zkw.prefix("Unable to list children of znode " + znode + " " +
+          "because node does not exist (not an error)"));
+      return null;
+    } catch (KeeperException e) {
+      LOG.warn(zkw.prefix("Unable to list children of znode " + znode + " "), e);
+      zkw.keeperException(e);
+      return null;
+    } catch (InterruptedException e) {
+      LOG.warn(zkw.prefix("Unable to list children of znode " + znode + " "), e);
+      zkw.interruptedException(e);
+      return null;
+    }
+  }
+
+  /**
+   * List all the children of the specified znode, setting a watch for children
+   * changes and also setting a watch on every individual child in order to get
+   * the NodeCreated and NodeDeleted events.
+   * @param zkw zookeeper reference
+   * @param znode node to get children of and watch
+   * @return list of znode names, null if the node doesn't exist
+   * @throws KeeperException
+   */
+  public static List<String> listChildrenAndWatchThem(ZKWatcher zkw,
+      String znode) throws KeeperException {
+    List<String> children = listChildrenAndWatchForNewChildren(zkw, znode);
+    if (children == null) {
+      return null;
+    }
+    for (String child : children) {
+      watchAndCheckExists(zkw, ZNodePaths.joinZNode(znode, child));
+    }
+    return children;
+  }
+
+  /**
+   * Lists the children of the specified znode without setting any watches.
+   *
+   * Sets no watches at all, this method is best effort.
+   *
+   * Returns an empty list if the node has no children.  Returns null if the
+   * parent node itself does not exist.
+   *
+   * @param zkw zookeeper reference
+   * @param znode node to get children
+   * @return list of data of children of specified znode, empty if no children,
+   *         null if parent does not exist
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static List<String> listChildrenNoWatch(ZKWatcher zkw, String znode)
+  throws KeeperException {
+    List<String> children = null;
+    try {
+      // List the children without watching
+      children = zkw.getRecoverableZooKeeper().getChildren(znode, null);
+    } catch(KeeperException.NoNodeException nne) {
+      return null;
+    } catch(InterruptedException ie) {
+      zkw.interruptedException(ie);
+    }
+    return children;
+  }
+
+  /**
+   * Simple class to hold a node path and node data.
+   * @deprecated Unused
+   */
+  @Deprecated
+  public static class NodeAndData {
+    private String node;
+    private byte [] data;
+    public NodeAndData(String node, byte [] data) {
+      this.node = node;
+      this.data = data;
+    }
+    public String getNode() {
+      return node;
+    }
+    public byte [] getData() {
+      return data;
+    }
+    @Override
+    public String toString() {
+      return node;
+    }
+    public boolean isEmpty() {
+      return (data == null || data.length == 0);
+    }
+  }
+
+  /**
+   * Checks if the specified znode has any children.  Sets no watches.
+   *
+   * Returns true if the node exists and has children.  Returns false if the
+   * node does not exist or if the node does not have any children.
+   *
+   * Used during master initialization to determine if the master is a
+   * failed-over-to master or the first master during initial cluster startup.
+   * If the directory for regionserver ephemeral nodes is empty then this is
+   * a cluster startup, if not then it is not cluster startup.
+   *
+   * @param zkw zk reference
+   * @param znode path of node to check for children of
+   * @return true if node has children, false if not or node does not exist
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static boolean nodeHasChildren(ZKWatcher zkw, String znode)
+  throws KeeperException {
+    try {
+      return !zkw.getRecoverableZooKeeper().getChildren(znode, null).isEmpty();
+    } catch(KeeperException.NoNodeException ke) {
+      LOG.debug(zkw.prefix("Unable to list children of znode " + znode + " " +
+      "because node does not exist (not an error)"));
+      return false;
+    } catch (KeeperException e) {
+      LOG.warn(zkw.prefix("Unable to list children of znode " + znode), e);
+      zkw.keeperException(e);
+      return false;
+    } catch (InterruptedException e) {
+      LOG.warn(zkw.prefix("Unable to list children of znode " + znode), e);
+      zkw.interruptedException(e);
+      return false;
+    }
+  }
+
+  /**
+   * Get the number of children of the specified node.
+   *
+   * If the node does not exist or has no children, returns 0.
+   *
+   * Sets no watches at all.
+   *
+   * @param zkw zk reference
+   * @param znode path of node to count children of
+   * @return number of children of specified node, 0 if none or parent does not
+   *         exist
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static int getNumberOfChildren(ZKWatcher zkw, String znode)
+  throws KeeperException {
+    try {
+      Stat stat = zkw.getRecoverableZooKeeper().exists(znode, null);
+      return stat == null ? 0 : stat.getNumChildren();
+    } catch(KeeperException e) {
+      LOG.warn(zkw.prefix("Unable to get children of node " + znode));
+      zkw.keeperException(e);
+    } catch(InterruptedException e) {
+      zkw.interruptedException(e);
+    }
+    return 0;
+  }
+
+  //
+  // Data retrieval
+  //
+
+  /**
+   * Get znode data. Does not set a watcher.
+   * @return ZNode data, null if the node does not exist or if there is an
+   *  error.
+   */
+  public static byte [] getData(ZKWatcher zkw, String znode)
+      throws KeeperException, InterruptedException {
+    try {
+      byte [] data = zkw.getRecoverableZooKeeper().getData(znode, null, null);
+      logRetrievedMsg(zkw, znode, data, false);
+      return data;
+    } catch (KeeperException.NoNodeException e) {
+      LOG.debug(zkw.prefix("Unable to get data of znode " + znode + " " +
+          "because node does not exist (not an error)"));
+      return null;
+    } catch (KeeperException e) {
+      LOG.warn(zkw.prefix("Unable to get data of znode " + znode), e);
+      zkw.keeperException(e);
+      return null;
+    }
+  }
+
+  /**
+   * Get the data at the specified znode and set a watch.
+   *
+   * Returns the data and sets a watch if the node exists.  Returns null and no
+   * watch is set if the node does not exist or there is an exception.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @return data of the specified znode, or null
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static byte [] getDataAndWatch(ZKWatcher zkw, String znode)
+  throws KeeperException {
+    return getDataInternal(zkw, znode, null, true);
+  }
+
+  /**
+   * Get the data at the specified znode and set a watch.
+   *
+   * Returns the data and sets a watch if the node exists.  Returns null and no
+   * watch is set if the node does not exist or there is an exception.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @param stat object to populate the version of the znode
+   * @return data of the specified znode, or null
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static byte[] getDataAndWatch(ZKWatcher zkw, String znode,
+                                       Stat stat) throws KeeperException {
+    return getDataInternal(zkw, znode, stat, true);
+  }
+
+  private static byte[] getDataInternal(ZKWatcher zkw, String znode, Stat stat,
+                                        boolean watcherSet)
+      throws KeeperException {
+    try {
+      byte [] data = zkw.getRecoverableZooKeeper().getData(znode, zkw, stat);
+      logRetrievedMsg(zkw, znode, data, watcherSet);
+      return data;
+    } catch (KeeperException.NoNodeException e) {
+      // This log can get pretty annoying when we cycle on 100ms waits.
+      // Enable trace if you really want to see it.
+      LOG.trace(zkw.prefix("Unable to get data of znode " + znode + " " +
+        "because node does not exist (not an error)"));
+      return null;
+    } catch (KeeperException e) {
+      LOG.warn(zkw.prefix("Unable to get data of znode " + znode), e);
+      zkw.keeperException(e);
+      return null;
+    } catch (InterruptedException e) {
+      LOG.warn(zkw.prefix("Unable to get data of znode " + znode), e);
+      zkw.interruptedException(e);
+      return null;
+    }
+  }
+
+  /**
+   * Get the data at the specified znode without setting a watch.
+   *
+   * Returns the data if the node exists.  Returns null if the node does not
+   * exist.
+   *
+   * Sets the stats of the node in the passed Stat object.  Pass a null stat if
+   * not interested.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @param stat node status to get if node exists
+   * @return data of the specified znode, or null if node does not exist
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static byte [] getDataNoWatch(ZKWatcher zkw, String znode,
+                                       Stat stat)
+  throws KeeperException {
+    try {
+      byte [] data = zkw.getRecoverableZooKeeper().getData(znode, null, stat);
+      logRetrievedMsg(zkw, znode, data, false);
+      return data;
+    } catch (KeeperException.NoNodeException e) {
+      LOG.debug(zkw.prefix("Unable to get data of znode " + znode + " " +
+          "because node does not exist (not necessarily an error)"));
+      return null;
+    } catch (KeeperException e) {
+      LOG.warn(zkw.prefix("Unable to get data of znode " + znode), e);
+      zkw.keeperException(e);
+      return null;
+    } catch (InterruptedException e) {
+      LOG.warn(zkw.prefix("Unable to get data of znode " + znode), e);
+      zkw.interruptedException(e);
+      return null;
+    }
+  }
+
+  /**
+   * Returns the date of child znodes of the specified znode.  Also sets a watch on
+   * the specified znode which will capture a NodeDeleted event on the specified
+   * znode as well as NodeChildrenChanged if any children of the specified znode
+   * are created or deleted.
+   *
+   * Returns null if the specified node does not exist.  Otherwise returns a
+   * list of children of the specified node.  If the node exists but it has no
+   * children, an empty list will be returned.
+   *
+   * @param zkw zk reference
+   * @param baseNode path of node to list and watch children of
+   * @return list of data of children of the specified node, an empty list if the node
+   *          exists but has no children, and null if the node does not exist
+   * @throws KeeperException if unexpected zookeeper exception
+   * @deprecated Unused
+   */
+  @Deprecated
+  public static List<NodeAndData> getChildDataAndWatchForNewChildren(
+          ZKWatcher zkw, String baseNode) throws KeeperException {
+    List<String> nodes =
+      ZKUtil.listChildrenAndWatchForNewChildren(zkw, baseNode);
+    if (nodes != null) {
+      List<NodeAndData> newNodes = new ArrayList<>();
+      for (String node : nodes) {
+        String nodePath = ZNodePaths.joinZNode(baseNode, node);
+        byte[] data = ZKUtil.getDataAndWatch(zkw, nodePath);
+        newNodes.add(new NodeAndData(nodePath, data));
+      }
+      return newNodes;
+    }
+    return null;
+  }
+
+  /**
+   * Update the data of an existing node with the expected version to have the
+   * specified data.
+   *
+   * Throws an exception if there is a version mismatch or some other problem.
+   *
+   * Sets no watches under any conditions.
+   *
+   * @param zkw zk reference
+   * @param znode
+   * @param data
+   * @param expectedVersion
+   * @throws KeeperException if unexpected zookeeper exception
+   * @throws KeeperException.BadVersionException if version mismatch
+   * @deprecated Unused
+   */
+  @Deprecated
+  public static void updateExistingNodeData(ZKWatcher zkw, String znode,
+                                            byte [] data, int expectedVersion)
+  throws KeeperException {
+    try {
+      zkw.getRecoverableZooKeeper().setData(znode, data, expectedVersion);
+    } catch(InterruptedException ie) {
+      zkw.interruptedException(ie);
+    }
+  }
+
+  //
+  // Data setting
+  //
+
+  /**
+   * Sets the data of the existing znode to be the specified data.  Ensures that
+   * the current data has the specified expected version.
+   *
+   * <p>If the node does not exist, a {@link NoNodeException} will be thrown.
+   *
+   * <p>If their is a version mismatch, method returns null.
+   *
+   * <p>No watches are set but setting data will trigger other watchers of this
+   * node.
+   *
+   * <p>If there is another problem, a KeeperException will be thrown.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @param data data to set for node
+   * @param expectedVersion version expected when setting data
+   * @return true if data set, false if version mismatch
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static boolean setData(ZKWatcher zkw, String znode,
+                                byte [] data, int expectedVersion)
+  throws KeeperException, KeeperException.NoNodeException {
+    try {
+      return zkw.getRecoverableZooKeeper().setData(znode, data, expectedVersion) != null;
+    } catch (InterruptedException e) {
+      zkw.interruptedException(e);
+      return false;
+    }
+  }
+
+  /**
+   * Set data into node creating node if it doesn't yet exist.
+   * Does not set watch.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @param data data to set for node
+   * @throws KeeperException
+   */
+  public static void createSetData(final ZKWatcher zkw, final String znode,
+                                   final byte [] data)
+  throws KeeperException {
+    if (checkExists(zkw, znode) == -1) {
+      ZKUtil.createWithParents(zkw, znode, data);
+    } else {
+      ZKUtil.setData(zkw, znode, data);
+    }
+  }
+
+  /**
+   * Sets the data of the existing znode to be the specified data.  The node
+   * must exist but no checks are done on the existing data or version.
+   *
+   * <p>If the node does not exist, a {@link NoNodeException} will be thrown.
+   *
+   * <p>No watches are set but setting data will trigger other watchers of this
+   * node.
+   *
+   * <p>If there is another problem, a KeeperException will be thrown.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @param data data to set for node
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static void setData(ZKWatcher zkw, String znode, byte [] data)
+  throws KeeperException, KeeperException.NoNodeException {
+    setData(zkw, (SetData)ZKUtilOp.setData(znode, data));
+  }
+
+  private static void setData(ZKWatcher zkw, SetData setData)
+  throws KeeperException, KeeperException.NoNodeException {
+    SetDataRequest sd = (SetDataRequest)toZooKeeperOp(zkw, setData).toRequestRecord();
+    setData(zkw, sd.getPath(), sd.getData(), sd.getVersion());
+  }
+
+  /**
+   * Returns whether or not secure authentication is enabled
+   * (whether <code>hbase.security.authentication</code> is set to
+   * <code>kerberos</code>.
+   */
+  public static boolean isSecureZooKeeper(Configuration conf) {
+    // Detection for embedded HBase client with jaas configuration
+    // defined for third party programs.
+    try {
+      javax.security.auth.login.Configuration testConfig =
+          javax.security.auth.login.Configuration.getConfiguration();
+      if (testConfig.getAppConfigurationEntry("Client") == null
+          && testConfig.getAppConfigurationEntry(
+            JaasConfiguration.CLIENT_KEYTAB_KERBEROS_CONFIG_NAME) == null
+          && testConfig.getAppConfigurationEntry(
+              JaasConfiguration.SERVER_KEYTAB_KERBEROS_CONFIG_NAME) == null
+          && conf.get(HConstants.ZK_CLIENT_KERBEROS_PRINCIPAL) == null
+          && conf.get(HConstants.ZK_SERVER_KERBEROS_PRINCIPAL) == null) {
+
+        return false;
+      }
+    } catch(Exception e) {
+      // No Jaas configuration defined.
+      return false;
+    }
+
+    // Master & RSs uses hbase.zookeeper.client.*
+    return "kerberos".equalsIgnoreCase(conf.get("hbase.security.authentication"));
+  }
+
+  private static ArrayList<ACL> createACL(ZKWatcher zkw, String node) {
+    return createACL(zkw, node, isSecureZooKeeper(zkw.getConfiguration()));
+  }
+
+  public static ArrayList<ACL> createACL(ZKWatcher zkw, String node,
+                                         boolean isSecureZooKeeper) {
+    if (!node.startsWith(zkw.znodePaths.baseZNode)) {
+      return Ids.OPEN_ACL_UNSAFE;
+    }
+    if (isSecureZooKeeper) {
+      ArrayList<ACL> acls = new ArrayList<>();
+      // add permission to hbase supper user
+      String[] superUsers = zkw.getConfiguration().getStrings(Superusers.SUPERUSER_CONF_KEY);
+      String hbaseUser = null;
+      try {
+        hbaseUser = UserGroupInformation.getCurrentUser().getShortUserName();
+      } catch (IOException e) {
+        LOG.debug("Could not acquire current User.", e);
+      }
+      if (superUsers != null) {
+        List<String> groups = new ArrayList<>();
+        for (String user : superUsers) {
+          if (AuthUtil.isGroupPrincipal(user)) {
+            // TODO: Set node ACL for groups when ZK supports this feature
+            groups.add(user);
+          } else {
+            if(!user.equals(hbaseUser)) {
+              acls.add(new ACL(Perms.ALL, new Id("sasl", user)));
+            }
+          }
+        }
+        if (!groups.isEmpty()) {
+          LOG.warn("Znode ACL setting for group " + groups
+              + " is skipped, ZooKeeper doesn't support this feature presently.");
+        }
+      }
+      // Certain znodes are accessed directly by the client,
+      // so they must be readable by non-authenticated clients
+      if (zkw.isClientReadable(node)) {
+        acls.addAll(Ids.CREATOR_ALL_ACL);
+        acls.addAll(Ids.READ_ACL_UNSAFE);
+      } else {
+        acls.addAll(Ids.CREATOR_ALL_ACL);
+      }
+      return acls;
+    } else {
+      return Ids.OPEN_ACL_UNSAFE;
+    }
+  }
+
+  //
+  // Node creation
+  //
+
+  /**
+   *
+   * Set the specified znode to be an ephemeral node carrying the specified
+   * data.
+   *
+   * If the node is created successfully, a watcher is also set on the node.
+   *
+   * If the node is not created successfully because it already exists, this
+   * method will also set a watcher on the node.
+   *
+   * If there is another problem, a KeeperException will be thrown.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @param data data of node
+   * @return true if node created, false if not, watch set in both cases
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static boolean createEphemeralNodeAndWatch(ZKWatcher zkw,
+      String znode, byte [] data)
+  throws KeeperException {
+    boolean ret = true;
+    try {
+      zkw.getRecoverableZooKeeper().create(znode, data, createACL(zkw, znode),
+          CreateMode.EPHEMERAL);
+    } catch (KeeperException.NodeExistsException nee) {
+      ret = false;
+    } catch (InterruptedException e) {
+      LOG.info("Interrupted", e);
+      Thread.currentThread().interrupt();
+    }
+    if(!watchAndCheckExists(zkw, znode)) {
+      // It did exist but now it doesn't, try again
+      return createEphemeralNodeAndWatch(zkw, znode, data);
+    }
+    return ret;
+  }
+
+  /**
+   * Creates the specified znode to be a persistent node carrying the specified
+   * data.
+   *
+   * Returns true if the node was successfully created, false if the node
+   * already existed.
+   *
+   * If the node is created successfully, a watcher is also set on the node.
+   *
+   * If the node is not created successfully because it already exists, this
+   * method will also set a watcher on the node but return false.
+   *
+   * If there is another problem, a KeeperException will be thrown.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @param data data of node
+   * @return true if node created, false if not, watch set in both cases
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static boolean createNodeIfNotExistsAndWatch(
+          ZKWatcher zkw, String znode, byte [] data)
+  throws KeeperException {
+    boolean ret = true;
+    try {
+      zkw.getRecoverableZooKeeper().create(znode, data, createACL(zkw, znode),
+          CreateMode.PERSISTENT);
+    } catch (KeeperException.NodeExistsException nee) {
+      ret = false;
+    } catch (InterruptedException e) {
+      zkw.interruptedException(e);
+      return false;
+    }
+    try {
+      zkw.getRecoverableZooKeeper().exists(znode, zkw);
+    } catch (InterruptedException e) {
+      zkw.interruptedException(e);
+      return false;
+    }
+    return ret;
+  }
+
+  /**
+   * Creates the specified znode with the specified data but does not watch it.
+   *
+   * Returns the znode of the newly created node
+   *
+   * If there is another problem, a KeeperException will be thrown.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @param data data of node
+   * @param createMode specifying whether the node to be created is ephemeral and/or sequential
+   * @return true name of the newly created znode or null
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static String createNodeIfNotExistsNoWatch(ZKWatcher zkw, String znode,
+                                                    byte[] data, CreateMode createMode) throws KeeperException {
+
+    String createdZNode = null;
+    try {
+      createdZNode = zkw.getRecoverableZooKeeper().create(znode, data,
+          createACL(zkw, znode), createMode);
+    } catch (KeeperException.NodeExistsException nee) {
+      return znode;
+    } catch (InterruptedException e) {
+      zkw.interruptedException(e);
+      return null;
+    }
+    return createdZNode;
+  }
+
+  /**
+   * Creates the specified node with the specified data and watches it.
+   *
+   * <p>Throws an exception if the node already exists.
+   *
+   * <p>The node created is persistent and open access.
+   *
+   * <p>Returns the version number of the created node if successful.
+   *
+   * @param zkw zk reference
+   * @param znode path of node to create
+   * @param data data of node to create
+   * @return version of node created
+   * @throws KeeperException if unexpected zookeeper exception
+   * @throws KeeperException.NodeExistsException if node already exists
+   */
+  public static int createAndWatch(ZKWatcher zkw,
+      String znode, byte [] data)
+  throws KeeperException, KeeperException.NodeExistsException {
+    try {
+      zkw.getRecoverableZooKeeper().create(znode, data, createACL(zkw, znode),
+          CreateMode.PERSISTENT);
+      Stat stat = zkw.getRecoverableZooKeeper().exists(znode, zkw);
+      if (stat == null){
+        // Likely a race condition. Someone deleted the znode.
+        throw KeeperException.create(KeeperException.Code.SYSTEMERROR,
+            "ZK.exists returned null (i.e.: znode does not exist) for znode=" + znode);
+      }
+     return stat.getVersion();
+    } catch (InterruptedException e) {
+      zkw.interruptedException(e);
+      return -1;
+    }
+  }
+
+  /**
+   * Async creates the specified node with the specified data.
+   *
+   * <p>Throws an exception if the node already exists.
+   *
+   * <p>The node created is persistent and open access.
+   *
+   * @param zkw zk reference
+   * @param znode path of node to create
+   * @param data data of node to create
+   * @param cb
+   * @param ctx
+   */
+  public static void asyncCreate(ZKWatcher zkw,
+      String znode, byte [] data, final AsyncCallback.StringCallback cb,
+      final Object ctx) {
+    zkw.getRecoverableZooKeeper().getZooKeeper().create(znode, data,
+        createACL(zkw, znode), CreateMode.PERSISTENT, cb, ctx);
+  }
+
+  /**
+   * Creates the specified node, iff the node does not exist.  Does not set a
+   * watch and fails silently if the node already exists.
+   *
+   * The node created is persistent and open access.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static void createAndFailSilent(ZKWatcher zkw,
+      String znode) throws KeeperException {
+    createAndFailSilent(zkw, znode, new byte[0]);
+  }
+
+  /**
+   * Creates the specified node containing specified data, iff the node does not exist.  Does
+   * not set a watch and fails silently if the node already exists.
+   *
+   * The node created is persistent and open access.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @param data a byte array data to store in the znode
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static void createAndFailSilent(ZKWatcher zkw,
+      String znode, byte[] data)
+  throws KeeperException {
+    createAndFailSilent(zkw,
+        (CreateAndFailSilent)ZKUtilOp.createAndFailSilent(znode, data));
+  }
+
+  private static void createAndFailSilent(ZKWatcher zkw, CreateAndFailSilent cafs)
+  throws KeeperException {
+    CreateRequest create = (CreateRequest)toZooKeeperOp(zkw, cafs).toRequestRecord();
+    String znode = create.getPath();
+    try {
+      RecoverableZooKeeper zk = zkw.getRecoverableZooKeeper();
+      if (zk.exists(znode, false) == null) {
+        zk.create(znode, create.getData(), create.getAcl(), CreateMode.fromFlag(create.getFlags()));
+      }
+    } catch(KeeperException.NodeExistsException nee) {
+    } catch(KeeperException.NoAuthException nee){
+      try {
+        if (null == zkw.getRecoverableZooKeeper().exists(znode, false)) {
+          // If we failed to create the file and it does not already exist.
+          throw(nee);
+        }
+      } catch (InterruptedException ie) {
+        zkw.interruptedException(ie);
+      }
+    } catch(InterruptedException ie) {
+      zkw.interruptedException(ie);
+    }
+  }
+
+  /**
+   * Creates the specified node and all parent nodes required for it to exist.
+   *
+   * No watches are set and no errors are thrown if the node already exists.
+   *
+   * The nodes created are persistent and open access.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static void createWithParents(ZKWatcher zkw, String znode)
+  throws KeeperException {
+    createWithParents(zkw, znode, new byte[0]);
+  }
+
+  /**
+   * Creates the specified node and all parent nodes required for it to exist.  The creation of
+   * parent znodes is not atomic with the leafe znode creation but the data is written atomically
+   * when the leaf node is created.
+   *
+   * No watches are set and no errors are thrown if the node already exists.
+   *
+   * The nodes created are persistent and open access.
+   *
+   * @param zkw zk reference
+   * @param znode path of node
+   * @throws KeeperException if unexpected zookeeper exception
+   */
+  public static void createWithParents(ZKWatcher zkw, String znode, byte[] data)
+  throws KeeperException {
+    try {
+      if(znode == null) {
+        return;
+      }
+      zkw.getRecoverableZooKeeper().create(znode, data, createACL(zkw, znode),
+          CreateMode.PERSISTENT);
+    } catch(KeeperException.NodeExistsException nee) {
+      return;
+    } catch(KeeperException.NoNodeException nne) {
+      createWithParents(zkw, getParent(znode));
+      createWithParents(zkw, znode, data);
+    } catch(InterruptedException ie) {
+      zkw.interruptedException(ie);
+    }
+  }
+
+  //
+  // Deletes
+  //
+
+  /**
+   * Delete the specified node.  Sets no watches.  Throws all exceptions.
+   */
+  public static void deleteNode(ZKWatcher zkw, String node)
+  throws KeeperException {
+    deleteNode(zkw, node, -1);
+  }
+
+  /**
+   * Delete the specified node with the specified version.  Sets no watches.
+   * Throws all exceptions.
+   */
+  public static boolean deleteNode(ZKWatcher zkw, String node,
+                                   int version)
+  throws KeeperException {
+    try {
+      zkw.getRecoverableZooKeeper().delete(node, version);
+      return true;
+    } catch(KeeperException.BadVersionException bve) {
+      return false;
+    } catch(InterruptedException ie) {
+      zkw.interruptedException(ie);
+      return false;
+    }
+  }
+
+  /**
+   * Deletes the specified node.  Fails silent if the node does not exist.
+   * @param zkw
+   * @param node
+   * @throws KeeperException
+   */
+  public static void deleteNodeFailSilent(ZKWatcher zkw, String node)
+  throws KeeperException {
+    deleteNodeFailSilent(zkw,
+      (DeleteNodeFailSilent)ZKUtilOp.deleteNodeFailSilent(node));
+  }
+
+  private static void deleteNodeFailSilent(ZKWatcher zkw,
+      DeleteNodeFailSilent dnfs) throws KeeperException {
+    DeleteRequest delete = (DeleteRequest)toZooKeeperOp(zkw, dnfs).toRequestRecord();
+    try {
+      zkw.getRecoverableZooKeeper().delete(delete.getPath(), delete.getVersion());
+    } catch(KeeperException.NoNodeException nne) {
+    } catch(InterruptedException ie) {
+      zkw.interruptedException(ie);
+    }
+  }
+
+
+  /**
+   * Delete the specified node and all of it's children.
+   * <p>
+   * If the node does not exist, just returns.
+   * <p>
+   * Sets no watches. Throws all exceptions besides dealing with deletion of
+   * children.
+   */
+  public static void deleteNodeRecursively(ZKWatcher zkw, String node)
+  throws KeeperException {
+    deleteNodeRecursivelyMultiOrSequential(zkw, true, node);
+  }
+
+  /**
+   * Delete all the children of the specified node but not the node itself.
+   *
+   * Sets no watches.  Throws all exceptions besides dealing with deletion of
+   * children.
+   *
+   * @throws KeeperException
+   */
+  public static void deleteChildrenRecursively(ZKWatcher zkw, String node)
+      throws KeeperException {
+    deleteChildrenRecursivelyMultiOrSequential(zkw, true, node);
+  }
+
+  /**
+   * Delete all the children of the specified node but not the node itself. This
+   * will first traverse the znode tree for listing the children and then delete
+   * these znodes using multi-update api or sequential based on the specified
+   * configurations.
+   * <p>
+   * Sets no watches. Throws all exceptions besides dealing with deletion of
+   * children.
+   * <p>
+   * If the following is true:
+   * <ul>
+   * <li>runSequentialOnMultiFailure is true
+   * </ul>
+   * on calling multi, we get a ZooKeeper exception that can be handled by a
+   * sequential call(*), we retry the operations one-by-one (sequentially).
+   *
+   * @param zkw
+   *          - zk reference
+   * @param runSequentialOnMultiFailure
+   *          - if true when we get a ZooKeeper exception that could retry the
+   *          operations one-by-one (sequentially)
+   * @param pathRoots
+   *          - path of the parent node(s)
+   * @throws KeeperException.NotEmptyException
+   *           if node has children while deleting
+   * @throws KeeperException
+   *           if unexpected ZooKeeper exception
+   * @throws IllegalArgumentException
+   *           if an invalid path is specified
+   */
+  public static void deleteChildrenRecursivelyMultiOrSequential(
+          ZKWatcher zkw, boolean runSequentialOnMultiFailure,
+          String... pathRoots) throws KeeperException {
+    if (pathRoots == null || pathRoots.length <= 0) {
+      LOG.warn("Given path is not valid!");
+      return;
+    }
+    List<ZKUtilOp> ops = new ArrayList<>();
+    for (String eachRoot : pathRoots) {
+      List<String> children = listChildrenBFSNoWatch(zkw, eachRoot);
+      // Delete the leaves first and eventually get rid of the root
+      for (int i = children.size() - 1; i >= 0; --i) {
+        ops.add(ZKUtilOp.deleteNodeFailSilent(children.get(i)));
+      }
+    }
+    // atleast one element should exist
+    if (ops.size() > 0) {
+      multiOrSequential(zkw, ops, runSequentialOnMultiFailure);
+    }
+  }
+
+  /**
+   * Delete the specified node and its children. This traverse the
+   * znode tree for listing the children and then delete
+   * these znodes including the parent using multi-update api or
+   * sequential based on the specified configurations.
+   * <p>
+   * Sets no watches. Throws all exceptions besides dealing with deletion of
+   * children.
+   * <p>
+   * If the following is true:
+   * <ul>
+   * <li>runSequentialOnMultiFailure is true
+   * </ul>
+   * on calling multi, we get a ZooKeeper exception that can be handled by a
+   * sequential call(*), we retry the operations one-by-one (sequentially).
+   *
+   * @param zkw
+   *          - zk reference
+   * @param runSequentialOnMultiFailure
+   *          - if true when we get a ZooKeeper exception that could retry the
+   *          operations one-by-one (sequentially)
+   * @param pathRoots
+   *          - path of the parent node(s)
+   * @throws KeeperException.NotEmptyException
+   *           if node has children while deleting
+   * @throws KeeperException
+   *           if unexpected ZooKeeper exception
+   * @throws IllegalArgumentException
+   *           if an invalid path is specified
+   */
+  public static void deleteNodeRecursivelyMultiOrSequential(ZKWatcher zkw,
+      boolean runSequentialOnMultiFailure, String... pathRoots) throws KeeperException {
+    if (pathRoots == null || pathRoots.length <= 0) {
+      LOG.warn("Given path is not valid!");
+      return;
+    }
+    List<ZKUtilOp> ops = new ArrayList<>();
+    for (String eachRoot : pathRoots) {
+      // ZooKeeper Watches are one time triggers; When children of parent nodes are deleted
+      // recursively, must set another watch, get notified of delete node
+      List<String> children = listChildrenBFSAndWatchThem(zkw, eachRoot);
+      // Delete the leaves first and eventually get rid of the root
+      for (int i = children.size() - 1; i >= 0; --i) {
+        ops.add(ZKUtilOp.deleteNodeFailSilent(children.get(i)));
+      }
+      try {
+        if (zkw.getRecoverableZooKeeper().exists(eachRoot, zkw) != null) {
+          ops.add(ZKUtilOp.deleteNodeFailSilent(eachRoot));
+        }
+      } catch (InterruptedException e) {
+        zkw.interruptedException(e);
+      }
+    }
+    // atleast one element should exist
+    if (ops.size() > 0) {
+      multiOrSequential(zkw, ops, runSequentialOnMultiFailure);
+    }
+  }
+
+  /**
+   * BFS Traversal of all the children under path, with the entries in the list,
+   * in the same order as that of the traversal. Lists all the children without
+   * setting any watches.
+   *
+   * @param zkw
+   *          - zk reference
+   * @param znode
+   *          - path of node
+   * @return list of children znodes under the path
+   * @throws KeeperException
+   *           if unexpected ZooKeeper exception
+   */
+  private static List<String> listChildrenBFSNoWatch(ZKWatcher zkw,
+      final String znode) throws KeeperException {
+    Deque<String> queue = new LinkedList<>();
+    List<String> tree = new ArrayList<>();
+    queue.add(znode);
+    while (true) {
+      String node = queue.pollFirst();
+      if (node == null) {
+        break;
+      }
+      List<String> children = listChildrenNoWatch(zkw, node);
+      if (children == null) {
+        continue;
+      }
+      for (final String child : children) {
+        final String childPath = node + "/" + child;
+        queue.add(childPath);
+        tree.add(childPath);
+      }
+    }
+    return tree;
+  }
+
+  /**
+   * BFS Traversal of all the children under path, with the entries in the list,
+   * in the same order as that of the traversal.
+   * Lists all the children and set watches on to them.
+   *
+   * @param zkw
+   *          - zk reference
+   * @param znode
+   *          - path of node
+   * @return list of children znodes under the path
+   * @throws KeeperException
+   *           if unexpected ZooKeeper exception
+   */
+  private static List<String> listChildrenBFSAndWatchThem(ZKWatcher zkw, final String znode)
+      throws KeeperException {
+    Deque<String> queue = new LinkedList<>();
+    List<String> tree = new ArrayList<>();
+    queue.add(znode);
+    while (true) {
+      String node = queue.pollFirst();
+      if (node == null) {
+        break;
+      }
+      List<String> children = listChildrenAndWatchThem(zkw, node);
+      if (children == null) {
+        continue;
+      }
+      for (final String child : children) {
+        final String childPath = node + "/" + child;
+        queue.add(childPath);
+        tree.add(childPath);
+      }
+    }
+    return tree;
+  }
+
+  /**
+   * Represents an action taken by ZKUtil, e.g. createAndFailSilent.
+   * These actions are higher-level than ZKOp actions, which represent
+   * individual actions in the ZooKeeper API, like create.
+   */
+  public abstract static class ZKUtilOp {
+    private String path;
+
+    private ZKUtilOp(String path) {
+      this.path = path;
+    }
+
+    /**
+     * @return a createAndFailSilent ZKUtilOp
+     */
+    public static ZKUtilOp createAndFailSilent(String path, byte[] data) {
+      return new CreateAndFailSilent(path, data);
+    }
+
+    /**
+     * @return a deleteNodeFailSilent ZKUtilOP
+     */
+    public static ZKUtilOp deleteNodeFailSilent(String path) {
+      return new DeleteNodeFailSilent(path);
+    }
+
+    /**
+     * @return a setData ZKUtilOp
+     */
+    public static ZKUtilOp setData(String path, byte [] data) {
+      return new SetData(path, data);
+    }
+
+    /**
+     * @return path to znode where the ZKOp will occur
+     */
+    public String getPath() {
+      return path;
+    }
+
+    /**
+     * ZKUtilOp representing createAndFailSilent in ZooKeeper
+     * (attempt to create node, ignore error if already exists)
+     */
+    public static class CreateAndFailSilent extends ZKUtilOp {
+      private byte [] data;
+
+      private CreateAndFailSilent(String path, byte [] data) {
+        super(path);
+        this.data = data;
+      }
+
+      public byte[] getData() {
+        return data;
+      }
+
+      @Override
+      public boolean equals(Object o) {
+        if (this == o) return true;
+        if (!(o instanceof CreateAndFailSilent)) return false;
+
+        CreateAndFailSilent op = (CreateAndFailSilent) o;
+        return getPath().equals(op.getPath()) && Arrays.equals(data, op.data);
+      }
+
+      @Override
+      public int hashCode() {
+        int ret = 17 + getPath().hashCode() * 31;
+        return ret * 31 + Bytes.hashCode(data);
+      }
+    }
+
+    /**
+     * ZKUtilOp representing deleteNodeFailSilent in ZooKeeper
+     * (attempt to delete node, ignore error if node doesn't exist)
+     */
+    public static class DeleteNodeFailSilent extends ZKUtilOp {
+      private DeleteNodeFailSilent(String path) {
+        super(path);
+      }
+
+      @Override
+      public boolean equals(Object o) {
+        if (this == o) return true;
+        if (!(o instanceof DeleteNodeFailSilent)) return false;
+
+        return super.equals(o);
+      }
+
+      @Override
+      public int hashCode() {
+        return getPath().hashCode();
+      }
+    }
+
+    /**
+     * ZKUtilOp representing setData in ZooKeeper
+     */
+    public static class SetData extends ZKUtilOp {
+      private byte [] data;
+
+      private SetData(String path, byte [] data) {
+        super(path);
+        this.data = data;
+      }
+
+      public byte[] getData() {
+        return data;
+      }
+
+      @Override
+      public boolean equals(Object o) {
+        if (this == o) return true;
+        if (!(o instanceof SetData)) return false;
+
+        SetData op = (SetData) o;
+        return getPath().equals(op.getPath()) && Arrays.equals(data, op.data);
+      }
+
+      @Override
+      public int hashCode() {
+        int ret = getPath().hashCode();
+        return ret * 31 + Bytes.hashCode(data);
+      }
+    }
+  }
+
+  /**
+   * Convert from ZKUtilOp to ZKOp
+   */
+  private static Op toZooKeeperOp(ZKWatcher zkw, ZKUtilOp op)
+  throws UnsupportedOperationException {
+    if(op == null) return null;
+
+    if (op instanceof CreateAndFailSilent) {
+      CreateAndFailSilent cafs = (CreateAndFailSilent)op;
+      return Op.create(cafs.getPath(), cafs.getData(), createACL(zkw, cafs.getPath()),
+        CreateMode.PERSISTENT);
+    } else if (op instanceof DeleteNodeFailSilent) {
+      DeleteNodeFailSilent dnfs = (DeleteNodeFailSilent)op;
+      return Op.delete(dnfs.getPath(), -1);
+    } else if (op instanceof SetData) {
+      SetData sd = (SetData)op;
+      return Op.setData(sd.getPath(), sd.getData(), -1);
+    } else {
+      throw new UnsupportedOperationException("Unexpected ZKUtilOp type: "
+        + op.getClass().getName());
+    }
+  }
+
+  /**
+   * Use ZooKeeper's multi-update functionality.
+   *
+   * If all of the following are true:
+   * - runSequentialOnMultiFailure is true
+   * - on calling multi, we get a ZooKeeper exception that can be handled by a sequential call(*)
+   * Then:
+   * - we retry the operations one-by-one (sequentially)
+   *
+   * Note *: an example is receiving a NodeExistsException from a "create" call.  Without multi,
+   * a user could call "createAndFailSilent" to ensure that a node exists if they don't care who
+   * actually created the node (i.e. the NodeExistsException from ZooKeeper is caught).
+   * This will cause all operations in the multi to fail, however, because
+   * the NodeExistsException that zk.create throws will fail the multi transaction.
+   * In this case, if the previous conditions hold, the commands are run sequentially, which should
+   * result in the correct final state, but means that the operations will not run atomically.
+   *
+   * @throws KeeperException
+   */
+  public static void multiOrSequential(ZKWatcher zkw, List<ZKUtilOp> ops,
+                                       boolean runSequentialOnMultiFailure) throws KeeperException {
+    if (zkw.getConfiguration().get("hbase.zookeeper.useMulti") != null) {
+      LOG.warn("hbase.zookeeper.useMulti is deprecated. Default to true always.");
+    }
+    if (ops == null) return;
+
+    List<Op> zkOps = new LinkedList<>();
+    for (ZKUtilOp op : ops) {
+      zkOps.add(toZooKeeperOp(zkw, op));
+    }
+    try {
+      zkw.getRecoverableZooKeeper().multi(zkOps);
+    } catch (KeeperException ke) {
+      switch (ke.code()) {
+      case NODEEXISTS:
+      case NONODE:
+      case BADVERSION:
+      case NOAUTH:
+        // if we get an exception that could be solved by running sequentially
+        // (and the client asked us to), then break out and run sequentially
+        if (runSequentialOnMultiFailure) {
+          LOG.info("On call to ZK.multi, received exception: " + ke.toString() + "."
+              + "  Attempting to run operations sequentially because"
+              + " runSequentialOnMultiFailure is: " + runSequentialOnMultiFailure + ".");
+          processSequentially(zkw, ops);
+          break;
+        }
+      default:
+        throw ke;
+      }
+    } catch (InterruptedException ie) {
+      zkw.interruptedException(ie);
+    }
+  }
+
+  private static void processSequentially(ZKWatcher zkw, List<ZKUtilOp> ops)
+      throws KeeperException, NoNodeException {
+    for (ZKUtilOp op : ops) {
+      if (op instanceof CreateAndFailSilent) {
+        createAndFailSilent(zkw, (CreateAndFailSilent) op);
+      } else if (op instanceof DeleteNodeFailSilent) {
+        deleteNodeFailSilent(zkw, (DeleteNodeFailSilent) op);
+      } else if (op instanceof SetData) {
+        setData(zkw, (SetData) op);
+      } else {
+        throw new UnsupportedOperationException("Unexpected ZKUtilOp type: "
+            + op.getClass().getName());
+      }
+    }
+  }
+
+  //
+  // ZooKeeper cluster information
+  //
+
+  /** @return String dump of everything in ZooKeeper. */
+  public static String dump(ZKWatcher zkw) {
+    StringBuilder sb = new StringBuilder();
+    try {
+      sb.append("HBase is rooted at ").append(zkw.znodePaths.baseZNode);
+      sb.append("\nActive master address: ");
+      try {
+        sb.append(MasterAddressTracker.getMasterAddress(zkw));
+      } catch (IOException e) {
+        sb.append("<<FAILED LOOKUP: " + e.getMessage() + ">>");
+      }
+      sb.append("\nBackup master addresses:");
+      for (String child : listChildrenNoWatch(zkw, zkw.znodePaths.backupMasterAddressesZNode)) {
+        sb.append("\n ").append(child);
+      }
+      sb.append("\nRegion server holding hbase:meta: "
+        + new MetaTableLocator().getMetaRegionLocation(zkw));
+      Configuration conf = HBaseConfiguration.create();
+      int numMetaReplicas = conf.getInt(HConstants.META_REPLICAS_NUM,
+               HConstants.DEFAULT_META_REPLICA_NUM);
+      for (int i = 1; i < numMetaReplicas; i++) {
+        sb.append("\nRegion server holding hbase:meta, replicaId " + i + " "
+                    + new MetaTableLocator().getMetaRegionLocation(zkw, i));
+      }
+      sb.append("\nRegion servers:");
+      for (String child : listChildrenNoWatch(zkw, zkw.znodePaths.rsZNode)) {
+        sb.append("\n ").append(child);
+      }
+      try {
+        getReplicationZnodesDump(zkw, sb);
+      } catch (KeeperException ke) {
+        LOG.warn("Couldn't get the replication znode dump", ke);
+      }
+      sb.append("\nQuorum Server Statistics:");
+      String[] servers = zkw.getQuorum().split(",");
+      for (String server : servers) {
+        sb.append("\n ").append(server);
+        try {
+          String[] stat = getServerStats(server, ZKUtil.zkDumpConnectionTimeOut);
+
+          if (stat == null) {
+            sb.append("[Error] invalid quorum server: " + server);
+            break;
+          }
+
+          for (String s : stat) {
+            sb.append("\n  ").append(s);
+          }
+        } catch (Exception e) {
+          sb.append("\n  ERROR: ").append(e.getMessage());
+        }
+      }
+    } catch (KeeperException ke) {
+      sb.append("\nFATAL ZooKeeper Exception!\n");
+      sb.append("\n" + ke.getMessage());
+    }
+    return sb.toString();
+  }
+
+  /**
+   * Appends replication znodes to the passed StringBuilder.
+   * @param zkw
+   * @param sb
+   * @throws KeeperException
+   */
+  private static void getReplicationZnodesDump(ZKWatcher zkw, StringBuilder sb)
+      throws KeeperException {
+    String replicationZnode = zkw.znodePaths.replicationZNode;
+    if (ZKUtil.checkExists(zkw, replicationZnode) == -1) return;
+    // do a ls -r on this znode
+    sb.append("\n").append(replicationZnode).append(": ");
+    List<String> children = ZKUtil.listChildrenNoWatch(zkw, replicationZnode);
+    for (String child : children) {
+      String znode = ZNodePaths.joinZNode(replicationZnode, child);
+      if (znode.equals(zkw.znodePaths.peersZNode)) {
+        appendPeersZnodes(zkw, znode, sb);
+      } else if (znode.equals(zkw.znodePaths.queuesZNode)) {
+        appendRSZnodes(zkw, znode, sb);
+      } else if (znode.equals(zkw.znodePaths.hfileRefsZNode)) {
+        appendHFileRefsZnodes(zkw, znode, sb);
+      }
+    }
+  }
+
+  private static void appendHFileRefsZnodes(ZKWatcher zkw, String hfileRefsZnode,
+                                            StringBuilder sb) throws KeeperException {
+    sb.append("\n").append(hfileRefsZnode).append(": ");
+    for (String peerIdZnode : ZKUtil.listChildrenNoWatch(zkw, hfileRefsZnode)) {
+      String znodeToProcess = ZNodePaths.joinZNode(hfileRefsZnode, peerIdZnode);
+      sb.append("\n").append(znodeToProcess).append(": ");
+      List<String> peerHFileRefsZnodes = ZKUtil.listChildrenNoWatch(zkw, znodeToProcess);
+      int size = peerHFileRefsZnodes.size();
+      for (int i = 0; i < size; i++) {
+        sb.append(peerHFileRefsZnodes.get(i));
+        if (i != size - 1) {
+          sb.append(", ");
+        }
+      }
+    }
+  }
+
+  /**
+   * Returns a string with replication znodes and position of the replication log
+   * @param zkw
+   * @return aq string of replication znodes and log positions
+   */
+  public static String getReplicationZnodesDump(ZKWatcher zkw) throws KeeperException {
+    StringBuilder sb = new StringBuilder();
+    getReplicationZnodesDump(zkw, sb);
+    return sb.toString();
+  }
+
+  private static void appendRSZnodes(ZKWatcher zkw, String znode, StringBuilder sb)
+      throws KeeperException {
+    List<String> stack = new LinkedList<>();
+    stack.add(znode);
+    do {
+      String znodeToProcess = stack.remove(stack.size() - 1);
+      sb.append("\n").append(znodeToProcess).append(": ");
+      byte[] data;
+      try {
+        data = ZKUtil.getData(zkw, znodeToProcess);
+      } catch (InterruptedException e) {
+        zkw.interruptedException(e);
+        return;
+      }
+      if (data != null && data.length > 0) { // log position
+        long position = 0;
+        try {
+          position = ZKUtil.parseWALPositionFrom(ZKUtil.getData(zkw, znodeToProcess));
+          sb.append(position);
+        } catch (DeserializationException ignored) {
+        } catch (InterruptedException e) {
+          zkw.interruptedException(e);
+          return;
+        }
+      }
+      for (String zNodeChild : ZKUtil.listChildrenNoWatch(zkw, znodeToProcess)) {
+        stack.add(ZNodePaths.joinZNode(znodeToProcess, zNodeChild));
+      }
+    } while (stack.size() > 0);
+  }
+
+  private static void appendPeersZnodes(ZKWatcher zkw, String peersZnode,
+                                        StringBuilder sb) throws KeeperException {
+    int pblen = ProtobufUtil.lengthOfPBMagic();
+    sb.append("\n").append(peersZnode).append(": ");
+    for (String peerIdZnode : ZKUtil.listChildrenNoWatch(zkw, peersZnode)) {
+      String znodeToProcess = ZNodePaths.joinZNode(peersZnode, peerIdZnode);
+      byte[] data;
+      try {
+        data = ZKUtil.getData(zkw, znodeToProcess);
+      } catch (InterruptedException e) {
+        zkw.interruptedException(e);
+        return;
+      }
+      // parse the data of the above peer znode.
+      try {
+        ReplicationProtos.ReplicationPeer.Builder builder =
+          ReplicationProtos.ReplicationPeer.newBuilder();
+        ProtobufUtil.mergeFrom(builder, data, pblen, data.length - pblen);
+        String clusterKey = builder.getClusterkey();
+        sb.append("\n").append(znodeToProcess).append(": ").append(clusterKey);
+        // add the peer-state.
+        appendPeerState(zkw, znodeToProcess, sb);
+      } catch (IOException ipbe) {
+        LOG.warn("Got Exception while parsing peer: " + znodeToProcess, ipbe);
+      }
+    }
+  }
+
+  private static void appendPeerState(ZKWatcher zkw, String znodeToProcess,
+                                      StringBuilder sb) throws KeeperException, InvalidProtocolBufferException {
+    String peerState = zkw.getConfiguration().get("zookeeper.znode.replication.peers.state",
+      "peer-state");
+    int pblen = ProtobufUtil.lengthOfPBMagic();
+    for (String child : ZKUtil.listChildrenNoWatch(zkw, znodeToProcess)) {
+      if (!child.equals(peerState)) continue;
+      String peerStateZnode = ZNodePaths.joinZNode(znodeToProcess, child);
+      sb.append("\n").append(peerStateZnode).append(": ");
+      byte[] peerStateData;
+      try {
+        peerStateData = ZKUtil.getData(zkw, peerStateZnode);
+        ReplicationProtos.ReplicationState.Builder builder =
+            ReplicationProtos.ReplicationState.newBuilder();
+        ProtobufUtil.mergeFrom(builder, peerStateData, pblen, peerStateData.length - pblen);
+        sb.append(builder.getState().name());
+      } catch (IOException ipbe) {
+        LOG.warn("Got Exception while parsing peer: " + znodeToProcess, ipbe);
+      } catch (InterruptedException e) {
+        zkw.interruptedException(e);
+        return;
+      }
+    }
+  }
+
+  /**
+   * Gets the statistics from the given server.
+   *
+   * @param server  The server to get the statistics from.
+   * @param timeout  The socket timeout to use.
+   * @return The array of response strings.
+   * @throws IOException When the socket communication fails.
+   */
+  public static String[] getServerStats(String server, int timeout)
+  throws IOException {
+    String[] sp = server.split(":");
+    if (sp == null || sp.length == 0) {
+      return null;
+    }
+
+    String host = sp[0];
+    int port = sp.length > 1 ? Integer.parseInt(sp[1])
+        : HConstants.DEFAULT_ZOOKEPER_CLIENT_PORT;
+
+    InetSocketAddress sockAddr = new InetSocketAddress(host, port);
+    try (Socket socket = new Socket()) {
+      socket.connect(sockAddr, timeout);
+
+      socket.setSoTimeout(timeout);
+      try (PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
+          BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()))) {
+        out.println("stat");
+        out.flush();
+        ArrayList<String> res = new ArrayList<>();
+        while (true) {
+          String line = in.readLine();
+          if (line != null) {
+            res.add(line);
+          } else {
+            break;
+          }
+        }
+        return res.toArray(new String[res.size()]);
+      }
+    }
+  }
+
+  private static void logRetrievedMsg(final ZKWatcher zkw,
+      final String znode, final byte [] data, final boolean watcherSet) {
+    if (!LOG.isTraceEnabled()) return;
+    LOG.trace(zkw.prefix("Retrieved " + ((data == null)? 0: data.length) +
+      " byte(s) of data from znode " + znode +
+      (watcherSet? " and set watcher; ": "; data=") +
+      (data == null? "null": data.length == 0? "empty": (
+          znode.startsWith(zkw.znodePaths.metaZNodePrefix)?
+            getServerNameOrEmptyString(data):
+          znode.startsWith(zkw.znodePaths.backupMasterAddressesZNode)?
+            getServerNameOrEmptyString(data):
+          StringUtils.abbreviate(Bytes.toStringBinary(data), 32)))));
+  }
+
+  private static String getServerNameOrEmptyString(final byte [] data) {
+    try {
+      return ProtobufUtil.parseServerNameFrom(data).toString();
+    } catch (DeserializationException e) {
+      return "";
+    }
+  }
+
+  /**
+   * Waits for HBase installation's base (parent) znode to become available.
+   * @throws IOException on ZK errors
+   */
+  public static void waitForBaseZNode(Configuration conf) throws IOException {
+    LOG.info("Waiting until the base znode is available");
+    String parentZNode = conf.get(HConstants.ZOOKEEPER_ZNODE_PARENT,
+        HConstants.DEFAULT_ZOOKEEPER_ZNODE_PARENT);
+    ZooKeeper zk = new ZooKeeper(ZKConfig.getZKQuorumServersString(conf),
+        conf.getInt(HConstants.ZK_SESSION_TIMEOUT,
+        HConstants.DEFAULT_ZK_SESSION_TIMEOUT), EmptyWatcher.instance);
+
+    final int maxTimeMs = 10000;
+    final int maxNumAttempts = maxTimeMs / HConstants.SOCKET_RETRY_WAIT_MS;
+
+    KeeperException keeperEx = null;
+    try {
+      try {
+        for (int attempt = 0; attempt < maxNumAttempts; ++attempt) {
+          try {
+            if (zk.exists(parentZNode, false) != null) {
+              LOG.info("Parent znode exists: " + parentZNode);
+              keeperEx = null;
+              break;
+            }
+          } catch (KeeperException e) {
+            keeperEx = e;
+          }
+          Threads.sleepWithoutInterrupt(HConstants.SOCKET_RETRY_WAIT_MS);
+        }
+      } finally {
+        zk.close();
+      }
+    } catch (InterruptedException ex) {
+      Thread.currentThread().interrupt();
+    }
+
+    if (keeperEx != null) {
+      throw new IOException(keeperEx);
+    }
+  }
+
+  /**
+   * Convert a {@link DeserializationException} to a more palatable {@link KeeperException}.
+   * Used when can't let a {@link DeserializationException} out w/o changing public API.
+   * @param e Exception to convert
+   * @return Converted exception
+   */
+  public static KeeperException convert(final DeserializationException e) {
+    KeeperException ke = new KeeperException.DataInconsistencyException();
+    ke.initCause(e);
+    return ke;
+  }
+
+  /**
+   * Recursively print the current state of ZK (non-transactional)
+   * @param root name of the root directory in zk to print
+   */
+  public static void logZKTree(ZKWatcher zkw, String root) {
+    if (!LOG.isDebugEnabled()) return;
+    LOG.debug("Current zk system:");
+    String prefix = "|-";
+    LOG.debug(prefix + root);
+    try {
+      logZKTree(zkw, root, prefix);
+    } catch (KeeperException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  /**
+   * Helper method to print the current state of the ZK tree.
+   * @see #logZKTree(ZKWatcher, String)
+   * @throws KeeperException if an unexpected exception occurs
+   */
+  protected static void logZKTree(ZKWatcher zkw, String root, String prefix)
+      throws KeeperException {
+    List<String> children = ZKUtil.listChildrenNoWatch(zkw, root);
+    if (children == null) return;
+    for (String child : children) {
+      LOG.debug(prefix + child);
+      String node = ZNodePaths.joinZNode(root.equals("/") ? "" : root, child);
+      logZKTree(zkw, node, prefix + "---");
+    }
+  }
+
+  /**
+   * @param position
+   * @return Serialized protobuf of <code>position</code> with pb magic prefix prepended suitable
+   *         for use as content of an wal position in a replication queue.
+   */
+  public static byte[] positionToByteArray(final long position) {
+    byte[] bytes = ReplicationProtos.ReplicationHLogPosition.newBuilder().setPosition(position)
+        .build().toByteArray();
+    return ProtobufUtil.prependPBMagic(bytes);
+  }
+
+  /**
+   * @param bytes - Content of a WAL position znode.
+   * @return long - The current WAL position.
+   * @throws DeserializationException
+   */
+  public static long parseWALPositionFrom(final byte[] bytes) throws DeserializationException {
+    if (bytes == null) {
+      throw new DeserializationException("Unable to parse null WAL position.");
+    }
+    if (ProtobufUtil.isPBMagicPrefix(bytes)) {
+      int pblen = ProtobufUtil.lengthOfPBMagic();
+      ReplicationProtos.ReplicationHLogPosition.Builder builder =
+          ReplicationProtos.ReplicationHLogPosition.newBuilder();
+      ReplicationProtos.ReplicationHLogPosition position;
+      try {
+        ProtobufUtil.mergeFrom(builder, bytes, pblen, bytes.length - pblen);
+        position = builder.build();
+      } catch (IOException e) {
+        throw new DeserializationException(e);
+      }
+      return position.getPosition();
+    } else {
+      if (bytes.length > 0) {
+        return Bytes.toLong(bytes);
+      }
+      return 0;
+    }
+  }
+}