HDFS-13443. RBF: Update mount table cache immediately after changing (add/update/remove) mount table entries. Contributed by Mohammad Arshad.

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/protocolPB/RouterAdminProtocolServerSideTranslatorPB.java

@@ -37,6 +37,8 @@ import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProt
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetSafeModeResponseProto;
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.LeaveSafeModeRequestProto;
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.LeaveSafeModeResponseProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RefreshMountTableEntriesRequestProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RefreshMountTableEntriesResponseProto;
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RemoveMountTableEntryRequestProto;
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RemoveMountTableEntryResponseProto;
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.UpdateMountTableEntryRequestProto;
@@ -58,6 +60,8 @@ import org.apache.hadoop.hdfs.server.federation.store.protocol.GetSafeModeReques
 import org.apache.hadoop.hdfs.server.federation.store.protocol.GetSafeModeResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.LeaveSafeModeRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.LeaveSafeModeResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateMountTableEntryRequest;
@@ -78,6 +82,8 @@ import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.GetSafeMo
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.GetSafeModeResponsePBImpl;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.LeaveSafeModeRequestPBImpl;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.LeaveSafeModeResponsePBImpl;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.RefreshMountTableEntriesRequestPBImpl;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.RefreshMountTableEntriesResponsePBImpl;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.RemoveMountTableEntryRequestPBImpl;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.RemoveMountTableEntryResponsePBImpl;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.UpdateMountTableEntryRequestPBImpl;
@@ -275,4 +281,21 @@ public class RouterAdminProtocolServerSideTranslatorPB implements
       throw new ServiceException(e);
     }
   }
+
+  @Override
+  public RefreshMountTableEntriesResponseProto refreshMountTableEntries(
+      RpcController controller, RefreshMountTableEntriesRequestProto request)
+      throws ServiceException {
+    try {
+      RefreshMountTableEntriesRequest req =
+          new RefreshMountTableEntriesRequestPBImpl(request);
+      RefreshMountTableEntriesResponse response =
+          server.refreshMountTableEntries(req);
+      RefreshMountTableEntriesResponsePBImpl responsePB =
+          (RefreshMountTableEntriesResponsePBImpl) response;
+      return responsePB.getProto();
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/protocolPB/RouterAdminProtocolTranslatorPB.java

@@ -38,6 +38,8 @@ import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProt
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetSafeModeResponseProto;
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.LeaveSafeModeRequestProto;
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.LeaveSafeModeResponseProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RefreshMountTableEntriesRequestProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RefreshMountTableEntriesResponseProto;
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RemoveMountTableEntryRequestProto;
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RemoveMountTableEntryResponseProto;
 import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.UpdateMountTableEntryRequestProto;
@@ -61,6 +63,8 @@ import org.apache.hadoop.hdfs.server.federation.store.protocol.GetSafeModeReques
 import org.apache.hadoop.hdfs.server.federation.store.protocol.GetSafeModeResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.LeaveSafeModeRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.LeaveSafeModeResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateMountTableEntryRequest;
@@ -77,6 +81,8 @@ import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.GetMountT
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.GetMountTableEntriesResponsePBImpl;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.GetSafeModeResponsePBImpl;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.LeaveSafeModeResponsePBImpl;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.RefreshMountTableEntriesRequestPBImpl;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.RefreshMountTableEntriesResponsePBImpl;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.RemoveMountTableEntryRequestPBImpl;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.RemoveMountTableEntryResponsePBImpl;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.UpdateMountTableEntryRequestPBImpl;
@@ -267,4 +273,19 @@ public class RouterAdminProtocolTranslatorPB
       throw new IOException(ProtobufHelper.getRemoteException(e).getMessage());
     }
   }
+
+  @Override
+  public RefreshMountTableEntriesResponse refreshMountTableEntries(
+      RefreshMountTableEntriesRequest request) throws IOException {
+    RefreshMountTableEntriesRequestPBImpl requestPB =
+        (RefreshMountTableEntriesRequestPBImpl) request;
+    RefreshMountTableEntriesRequestProto proto = requestPB.getProto();
+    try {
+      RefreshMountTableEntriesResponseProto response =
+          rpcProxy.refreshMountTableEntries(null, proto);
+      return new RefreshMountTableEntriesResponsePBImpl(response);
+    } catch (ServiceException e) {
+      throw new IOException(ProtobufHelper.getRemoteException(e).getMessage());
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/MountTableManager.java

@@ -23,6 +23,8 @@ import org.apache.hadoop.hdfs.server.federation.store.protocol.AddMountTableEntr
 import org.apache.hadoop.hdfs.server.federation.store.protocol.AddMountTableEntryResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.GetMountTableEntriesRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.GetMountTableEntriesResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateMountTableEntryRequest;
@@ -77,4 +79,18 @@ public interface MountTableManager {
    */
   GetMountTableEntriesResponse getMountTableEntries(
       GetMountTableEntriesRequest request) throws IOException;
+
+  /**
+   * Refresh mount table entries cache from the state store. Cache is updated
+   * periodically but with this API cache can be refreshed immediately. This API
+   * is primarily meant to be called from the Admin Server. Admin Server will
+   * call this API and refresh mount table cache of all the routers while
+   * changing mount table entries.
+   *
+   * @param request Fully populated request object.
+   * @return True the mount table entry was updated without any error.
+   * @throws IOException Throws exception if the data store is not initialized.
+   */
+  RefreshMountTableEntriesResponse refreshMountTableEntries(
+      RefreshMountTableEntriesRequest request) throws IOException;
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/MountTableRefresherService.java

@@ -0,0 +1,289 @@
+/**
+ * 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.hdfs.server.federation.router;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.server.federation.store.MountTableStore;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreUnavailableException;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreUtils;
+import org.apache.hadoop.hdfs.server.federation.store.records.RouterState;
+import org.apache.hadoop.net.NetUtils;
+import org.apache.hadoop.service.AbstractService;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.cache.CacheBuilder;
+import com.google.common.cache.CacheLoader;
+import com.google.common.cache.LoadingCache;
+import com.google.common.cache.RemovalListener;
+import com.google.common.cache.RemovalNotification;
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
+
+/**
+ * This service is invoked from {@link MountTableStore} when there is change in
+ * mount table entries and it updates mount table entry cache on local router as
+ * well as on all remote routers. Refresh on local router is done by calling
+ * {@link MountTableStore#loadCache(boolean)}} API directly, no RPC call
+ * involved, but on remote routers refresh is done through RouterClient(RPC
+ * call). To improve performance, all routers are refreshed in separate thread
+ * and all connection are cached. Cached connections are removed from
+ * cache and closed when their max live time is elapsed.
+ */
+public class MountTableRefresherService extends AbstractService {
+  private static final String ROUTER_CONNECT_ERROR_MSG =
+      "Router {} connection failed. Mount table cache will not refesh.";
+  private static final Logger LOG =
+      LoggerFactory.getLogger(MountTableRefresherService.class);
+
+  /** Local router. */
+  private final Router router;
+  /** Mount table store. */
+  private MountTableStore mountTableStore;
+  /** Local router admin address in the form of host:port. */
+  private String localAdminAdress;
+  /** Timeout in ms to update mount table cache on all the routers. */
+  private long cacheUpdateTimeout;
+
+  /**
+   * All router admin clients cached. So no need to create the client again and
+   * again. Router admin address(host:port) is used as key to cache RouterClient
+   * objects.
+   */
+  private LoadingCache<String, RouterClient> routerClientsCache;
+
+  /**
+   * Removes expired RouterClient from routerClientsCache.
+   */
+  private ScheduledExecutorService clientCacheCleanerScheduler;
+
+  /**
+   * Create a new service to refresh mount table cache when there is change in
+   * mount table entries.
+   *
+   * @param router whose mount table cache will be refreshed
+   */
+  public MountTableRefresherService(Router router) {
+    super(MountTableRefresherService.class.getSimpleName());
+    this.router = router;
+  }
+
+  @Override
+  protected void serviceInit(Configuration conf) throws Exception {
+    super.serviceInit(conf);
+    this.mountTableStore = getMountTableStore();
+    // attach this service to mount table store.
+    this.mountTableStore.setRefreshService(this);
+    this.localAdminAdress =
+        StateStoreUtils.getHostPortString(router.getAdminServerAddress());
+    this.cacheUpdateTimeout = conf.getTimeDuration(
+        RBFConfigKeys.MOUNT_TABLE_CACHE_UPDATE_TIMEOUT,
+        RBFConfigKeys.MOUNT_TABLE_CACHE_UPDATE_TIMEOUT_DEFAULT,
+        TimeUnit.MILLISECONDS);
+    long routerClientMaxLiveTime = conf.getTimeDuration(
+        RBFConfigKeys.MOUNT_TABLE_CACHE_UPDATE_CLIENT_MAX_TIME,
+        RBFConfigKeys.MOUNT_TABLE_CACHE_UPDATE_CLIENT_MAX_TIME_DEFAULT,
+        TimeUnit.MILLISECONDS);
+    routerClientsCache = CacheBuilder.newBuilder()
+        .expireAfterWrite(routerClientMaxLiveTime, TimeUnit.MILLISECONDS)
+        .removalListener(getClientRemover()).build(getClientCreator());
+
+    initClientCacheCleaner(routerClientMaxLiveTime);
+  }
+
+  private void initClientCacheCleaner(long routerClientMaxLiveTime) {
+    clientCacheCleanerScheduler =
+        Executors.newSingleThreadScheduledExecutor(new ThreadFactoryBuilder()
+        .setNameFormat("MountTableRefresh_ClientsCacheCleaner")
+        .setDaemon(true).build());
+    /*
+     * When cleanUp() method is called, expired RouterClient will be removed and
+     * closed.
+     */
+    clientCacheCleanerScheduler.scheduleWithFixedDelay(
+        () -> routerClientsCache.cleanUp(), routerClientMaxLiveTime,
+        routerClientMaxLiveTime, TimeUnit.MILLISECONDS);
+  }
+
+  /**
+   * Create cache entry remove listener.
+   */
+  private RemovalListener<String, RouterClient> getClientRemover() {
+    return new RemovalListener<String, RouterClient>() {
+      @Override
+      public void onRemoval(
+          RemovalNotification<String, RouterClient> notification) {
+          closeRouterClient(notification.getValue());
+      }
+    };
+  }
+
+  @VisibleForTesting
+  protected void closeRouterClient(RouterClient client) {
+    try {
+      client.close();
+    } catch (IOException e) {
+      LOG.error("Error while closing RouterClient", e);
+    }
+  }
+
+  /**
+   * Creates RouterClient and caches it.
+   */
+  private CacheLoader<String, RouterClient> getClientCreator() {
+    return new CacheLoader<String, RouterClient>() {
+      public RouterClient load(String adminAddress) throws IOException {
+        InetSocketAddress routerSocket =
+            NetUtils.createSocketAddr(adminAddress);
+        Configuration config = getConfig();
+        return createRouterClient(routerSocket, config);
+      }
+    };
+  }
+
+  @VisibleForTesting
+  protected RouterClient createRouterClient(InetSocketAddress routerSocket,
+      Configuration config) throws IOException {
+    return new RouterClient(routerSocket, config);
+  }
+
+  @Override
+  protected void serviceStart() throws Exception {
+    super.serviceStart();
+  }
+
+  @Override
+  protected void serviceStop() throws Exception {
+    super.serviceStop();
+    clientCacheCleanerScheduler.shutdown();
+    // remove and close all admin clients
+    routerClientsCache.invalidateAll();
+  }
+
+  private MountTableStore getMountTableStore() throws IOException {
+    MountTableStore mountTblStore =
+        router.getStateStore().getRegisteredRecordStore(MountTableStore.class);
+    if (mountTblStore == null) {
+      throw new IOException("Mount table state store is not available.");
+    }
+    return mountTblStore;
+  }
+
+  /**
+   * Refresh mount table cache of this router as well as all other routers.
+   */
+  public void refresh() throws StateStoreUnavailableException {
+    List<RouterState> cachedRecords =
+        router.getRouterStateManager().getCachedRecords();
+    List<MountTableRefresherThread> refreshThreads = new ArrayList<>();
+    for (RouterState routerState : cachedRecords) {
+      String adminAddress = routerState.getAdminAddress();
+      if (adminAddress == null || adminAddress.length() == 0) {
+        // this router has not enabled router admin
+        continue;
+      }
+      // No use of calling refresh on router which is not running state
+      if (routerState.getStatus() != RouterServiceState.RUNNING) {
+        LOG.info(
+            "Router {} is not running. Mount table cache will not refesh.");
+        // remove if RouterClient is cached.
+        removeFromCache(adminAddress);
+      } else if (isLocalAdmin(adminAddress)) {
+        /*
+         * Local router's cache update does not require RPC call, so no need for
+         * RouterClient
+         */
+        refreshThreads.add(getLocalRefresher(adminAddress));
+      } else {
+        try {
+          RouterClient client = routerClientsCache.get(adminAddress);
+          refreshThreads.add(new MountTableRefresherThread(
+              client.getMountTableManager(), adminAddress));
+        } catch (ExecutionException execExcep) {
+          // Can not connect, seems router is stopped now.
+          LOG.warn(ROUTER_CONNECT_ERROR_MSG, adminAddress, execExcep);
+        }
+      }
+    }
+    if (!refreshThreads.isEmpty()) {
+      invokeRefresh(refreshThreads);
+    }
+  }
+
+  @VisibleForTesting
+  protected MountTableRefresherThread getLocalRefresher(String adminAddress) {
+    return new MountTableRefresherThread(router.getAdminServer(), adminAddress);
+  }
+
+  private void removeFromCache(String adminAddress) {
+    routerClientsCache.invalidate(adminAddress);
+  }
+
+  private void invokeRefresh(List<MountTableRefresherThread> refreshThreads) {
+    CountDownLatch countDownLatch = new CountDownLatch(refreshThreads.size());
+    // start all the threads
+    for (MountTableRefresherThread refThread : refreshThreads) {
+      refThread.setCountDownLatch(countDownLatch);
+      refThread.start();
+    }
+    try {
+      /*
+       * Wait for all the thread to complete, await method returns false if
+       * refresh is not finished within specified time
+       */
+      boolean allReqCompleted =
+          countDownLatch.await(cacheUpdateTimeout, TimeUnit.MILLISECONDS);
+      if (!allReqCompleted) {
+        LOG.warn("Not all router admins updated their cache");
+      }
+    } catch (InterruptedException e) {
+      LOG.error("Mount table cache refresher was interrupted.", e);
+    }
+    logResult(refreshThreads);
+  }
+
+  private boolean isLocalAdmin(String adminAddress) {
+    return adminAddress.contentEquals(localAdminAdress);
+  }
+
+  private void logResult(List<MountTableRefresherThread> refreshThreads) {
+    int succesCount = 0;
+    int failureCount = 0;
+    for (MountTableRefresherThread mountTableRefreshThread : refreshThreads) {
+      if (mountTableRefreshThread.isSuccess()) {
+        succesCount++;
+      } else {
+        failureCount++;
+        // remove RouterClient from cache so that new client is created
+        removeFromCache(mountTableRefreshThread.getAdminAddress());
+      }
+    }
+    LOG.info("Mount table entries cache refresh succesCount={},failureCount={}",
+        succesCount, failureCount);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/MountTableRefresherThread.java

@@ -0,0 +1,96 @@
+/**
+ * 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.hdfs.server.federation.router;
+
+import java.io.IOException;
+import java.util.concurrent.CountDownLatch;
+
+import org.apache.hadoop.hdfs.server.federation.resolver.MountTableManager;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesResponse;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Base class for updating mount table cache on all the router.
+ */
+public class MountTableRefresherThread extends Thread {
+  private static final Logger LOG =
+      LoggerFactory.getLogger(MountTableRefresherThread.class);
+  private boolean success;
+  /** Admin server on which refreshed to be invoked. */
+  private String adminAddress;
+  private CountDownLatch countDownLatch;
+  private MountTableManager manager;
+
+  public MountTableRefresherThread(MountTableManager manager,
+      String adminAddress) {
+    this.manager = manager;
+    this.adminAddress = adminAddress;
+    setName("MountTableRefresh_" + adminAddress);
+    setDaemon(true);
+  }
+
+  /**
+   * Refresh mount table cache of local and remote routers. Local and remote
+   * routers will be refreshed differently. Lets understand what are the
+   * local and remote routers and refresh will be done differently on these
+   * routers. Suppose there are three routers R1, R2 and R3. User want to add
+   * new mount table entry. He will connect to only one router, not all the
+   * routers. Suppose He connects to R1 and calls add mount table entry through
+   * API or CLI. Now in this context R1 is local router, R2 and R3 are remote
+   * routers. Because add mount table entry is invoked on R1, R1 will update the
+   * cache locally it need not to make RPC call. But R1 will make RPC calls to
+   * update cache on R2 and R3.
+   */
+  @Override
+  public void run() {
+    try {
+      RefreshMountTableEntriesResponse refreshMountTableEntries =
+          manager.refreshMountTableEntries(
+              RefreshMountTableEntriesRequest.newInstance());
+      success = refreshMountTableEntries.getResult();
+    } catch (IOException e) {
+      LOG.error("Failed to refresh mount table entries cache at router {}",
+          adminAddress, e);
+    } finally {
+      countDownLatch.countDown();
+    }
+  }
+
+  /**
+   * @return true if cache was refreshed successfully.
+   */
+  public boolean isSuccess() {
+    return success;
+  }
+
+  public void setCountDownLatch(CountDownLatch countDownLatch) {
+    this.countDownLatch = countDownLatch;
+  }
+
+  @Override
+  public String toString() {
+    return "MountTableRefreshThread [success=" + success + ", adminAddress="
+        + adminAddress + "]";
+  }
+
+  public String getAdminAddress() {
+    return adminAddress;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RBFConfigKeys.java

@@ -204,6 +204,31 @@ public class RBFConfigKeys extends CommonConfigurationKeysPublic {
       FEDERATION_ROUTER_PREFIX + "mount-table.max-cache-size";
   /** Remove cache entries if we have more than 10k. */
   public static final int FEDERATION_MOUNT_TABLE_MAX_CACHE_SIZE_DEFAULT = 10000;
+  /**
+   * If true then cache updated immediately after mount table entry change
+   * otherwise it is updated periodically based configuration.
+   */
+  public static final String MOUNT_TABLE_CACHE_UPDATE =
+      FEDERATION_ROUTER_PREFIX + "mount-table.cache.update";
+  public static final boolean MOUNT_TABLE_CACHE_UPDATE_DEFAULT =
+      false;
+  /**
+   * Timeout to update mount table cache on all the routers.
+   */
+  public static final String MOUNT_TABLE_CACHE_UPDATE_TIMEOUT =
+      FEDERATION_ROUTER_PREFIX + "mount-table.cache.update.timeout";
+  public static final long MOUNT_TABLE_CACHE_UPDATE_TIMEOUT_DEFAULT =
+      TimeUnit.MINUTES.toMillis(1);
+  /**
+   * Remote router mount table cache is updated through RouterClient(RPC call).
+   * To improve performance, RouterClient connections are cached but it should
+   * not be kept in cache forever. This property defines the max time a
+   * connection can be cached.
+   */
+  public static final String MOUNT_TABLE_CACHE_UPDATE_CLIENT_MAX_TIME =
+      FEDERATION_ROUTER_PREFIX + "mount-table.cache.update.client.max.time";
+  public static final long MOUNT_TABLE_CACHE_UPDATE_CLIENT_MAX_TIME_DEFAULT =
+      TimeUnit.MINUTES.toMillis(5);
   public static final String FEDERATION_MOUNT_TABLE_CACHE_ENABLE =
       FEDERATION_ROUTER_PREFIX + "mount-table.cache.enable";
   public static final boolean FEDERATION_MOUNT_TABLE_CACHE_ENABLE_DEFAULT =

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/Router.java

@@ -254,9 +254,50 @@ public class Router extends CompositeService {
       addService(this.safemodeService);
     }
 
+    /*
+     * Refresh mount table cache immediately after adding, modifying or deleting
+     * the mount table entries. If this service is not enabled mount table cache
+     * are refreshed periodically by StateStoreCacheUpdateService
+     */
+    if (conf.getBoolean(RBFConfigKeys.MOUNT_TABLE_CACHE_UPDATE,
+        RBFConfigKeys.MOUNT_TABLE_CACHE_UPDATE_DEFAULT)) {
+      // There is no use of starting refresh service if state store and admin
+      // servers are not enabled
+      String disabledDependentServices = getDisabledDependentServices();
+      /*
+       * disabledDependentServices null means all dependent services are
+       * enabled.
+       */
+      if (disabledDependentServices == null) {
+
+        MountTableRefresherService refreshService =
+            new MountTableRefresherService(this);
+        addService(refreshService);
+        LOG.info("Service {} is enabled.",
+            MountTableRefresherService.class.getSimpleName());
+      } else {
+        LOG.warn(
+            "Service {} not enabled: depenendent service(s) {} not enabled.",
+            MountTableRefresherService.class.getSimpleName(),
+            disabledDependentServices);
+      }
+    }
+
     super.serviceInit(conf);
   }
 
+  private String getDisabledDependentServices() {
+    if (this.stateStore == null && this.adminServer == null) {
+      return StateStoreService.class.getSimpleName() + ","
+          + RouterAdminServer.class.getSimpleName();
+    } else if (this.stateStore == null) {
+      return StateStoreService.class.getSimpleName();
+    } else if (this.adminServer == null) {
+      return RouterAdminServer.class.getSimpleName();
+    }
+    return null;
+  }
+
   /**
    * Returns the hostname for this Router. If the hostname is not
    * explicitly configured in the given config, then it is determined.
@@ -696,9 +737,19 @@ public class Router extends CompositeService {
   }
 
   /**
-   * Get the Router safe mode service
+   * Get the Router safe mode service.
    */
   RouterSafemodeService getSafemodeService() {
     return this.safemodeService;
   }
+
+  /**
+   * Get router admin server.
+   *
+   * @return Null if admin is not enabled.
+   */
+  public RouterAdminServer getAdminServer() {
+    return adminServer;
+  }
+
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterAdminServer.java

@@ -39,6 +39,7 @@ import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamespaceInfo
 import org.apache.hadoop.hdfs.server.federation.resolver.MountTableManager;
 import org.apache.hadoop.hdfs.server.federation.store.DisabledNameserviceStore;
 import org.apache.hadoop.hdfs.server.federation.store.MountTableStore;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreCache;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.AddMountTableEntryRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.AddMountTableEntryResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.DisableNameserviceRequest;
@@ -55,6 +56,8 @@ import org.apache.hadoop.hdfs.server.federation.store.protocol.GetSafeModeReques
 import org.apache.hadoop.hdfs.server.federation.store.protocol.GetSafeModeResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.LeaveSafeModeRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.LeaveSafeModeResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateMountTableEntryRequest;
@@ -102,6 +105,7 @@ public class RouterAdminServer extends AbstractService
   private static String routerOwner;
   private static String superGroup;
   private static boolean isPermissionEnabled;
+  private boolean iStateStoreCache;
 
   public RouterAdminServer(Configuration conf, Router router)
       throws IOException {
@@ -154,6 +158,8 @@ public class RouterAdminServer extends AbstractService
     this.adminAddress = new InetSocketAddress(
         confRpcAddress.getHostName(), listenAddress.getPort());
     router.setAdminServerAddress(this.adminAddress);
+    iStateStoreCache =
+        router.getSubclusterResolver() instanceof StateStoreCache;
   }
 
   /**
@@ -243,7 +249,7 @@ public class RouterAdminServer extends AbstractService
         getMountTableStore().updateMountTableEntry(request);
 
     MountTable mountTable = request.getEntry();
-    if (mountTable != null) {
+    if (mountTable != null && router.isQuotaEnabled()) {
       synchronizeQuota(mountTable);
     }
     return response;
@@ -331,6 +337,26 @@ public class RouterAdminServer extends AbstractService
     return GetSafeModeResponse.newInstance(isInSafeMode);
   }
 
+  @Override
+  public RefreshMountTableEntriesResponse refreshMountTableEntries(
+      RefreshMountTableEntriesRequest request) throws IOException {
+    if (iStateStoreCache) {
+      /*
+       * MountTableResolver updates MountTableStore cache also. Expecting other
+       * SubclusterResolver implementations to update MountTableStore cache also
+       * apart from updating its cache.
+       */
+      boolean result = ((StateStoreCache) this.router.getSubclusterResolver())
+          .loadCache(true);
+      RefreshMountTableEntriesResponse response =
+          RefreshMountTableEntriesResponse.newInstance();
+      response.setResult(result);
+      return response;
+    } else {
+      return getMountTableStore().refreshMountTableEntries(request);
+    }
+  }
+
   /**
    * Verify if Router set safe mode state correctly.
    * @param isInSafeMode Expected state to be set.

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterHeartbeatService.java

@@ -29,6 +29,7 @@ import org.apache.hadoop.hdfs.server.federation.store.MountTableStore;
 import org.apache.hadoop.hdfs.server.federation.store.RecordStore;
 import org.apache.hadoop.hdfs.server.federation.store.RouterStore;
 import org.apache.hadoop.hdfs.server.federation.store.StateStoreService;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreUtils;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RouterHeartbeatRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RouterHeartbeatResponse;
 import org.apache.hadoop.hdfs.server.federation.store.records.BaseRecord;
@@ -91,6 +92,10 @@ public class RouterHeartbeatService extends PeriodicService {
             getStateStoreVersion(MembershipStore.class),
             getStateStoreVersion(MountTableStore.class));
         record.setStateStoreVersion(stateStoreVersion);
+        // if admin server not started then hostPort will be empty
+        String hostPort =
+            StateStoreUtils.getHostPortString(router.getAdminServerAddress());
+        record.setAdminAddress(hostPort);
         RouterHeartbeatRequest request =
             RouterHeartbeatRequest.newInstance(record);
         RouterHeartbeatResponse response = routerStore.routerHeartbeat(request);

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/MountTableStore.java

@@ -20,8 +20,11 @@ package org.apache.hadoop.hdfs.server.federation.store;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.hdfs.server.federation.resolver.MountTableManager;
+import org.apache.hadoop.hdfs.server.federation.router.MountTableRefresherService;
 import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreDriver;
 import org.apache.hadoop.hdfs.server.federation.store.records.MountTable;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Management API for the HDFS mount table information stored in
@@ -42,8 +45,29 @@ import org.apache.hadoop.hdfs.server.federation.store.records.MountTable;
 @InterfaceStability.Evolving
 public abstract class MountTableStore extends CachedRecordStore<MountTable>
     implements MountTableManager {
+  private static final Logger LOG =
+      LoggerFactory.getLogger(MountTableStore.class);
+  private MountTableRefresherService refreshService;
 
   public MountTableStore(StateStoreDriver driver) {
     super(MountTable.class, driver);
   }
+
+  public void setRefreshService(MountTableRefresherService refreshService) {
+    this.refreshService = refreshService;
+  }
+
+  /**
+   * Update mount table cache of this router as well as all other routers.
+   */
+  protected void updateCacheAllRouters() {
+    if (refreshService != null) {
+      try {
+        refreshService.refresh();
+      } catch (StateStoreUnavailableException e) {
+        LOG.error("Cannot refresh mount table: state store not available", e);
+      }
+    }
+  }
+
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/StateStoreUtils.java

@@ -17,6 +17,9 @@
  */
 package org.apache.hadoop.hdfs.server.federation.store;
 
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.net.UnknownHostException;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -110,4 +113,27 @@ public final class StateStoreUtils {
     }
     return matchingList;
   }
+
+  /**
+   * Returns address in form of host:port, empty string if address is null.
+   *
+   * @param address address
+   * @return host:port
+   */
+  public static String getHostPortString(InetSocketAddress address) {
+    if (null == address) {
+      return "";
+    }
+    String hostName = address.getHostName();
+    if (hostName.equals("0.0.0.0")) {
+      try {
+        hostName = InetAddress.getLocalHost().getHostName();
+      } catch (UnknownHostException e) {
+        LOG.error("Failed to get local host name", e);
+        return "";
+      }
+    }
+    return hostName + ":" + address.getPort();
+  }
+
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/impl/MountTableStoreImpl.java

@@ -33,6 +33,8 @@ import org.apache.hadoop.hdfs.server.federation.store.protocol.AddMountTableEntr
 import org.apache.hadoop.hdfs.server.federation.store.protocol.AddMountTableEntryResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.GetMountTableEntriesRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.GetMountTableEntriesResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateMountTableEntryRequest;
@@ -68,6 +70,7 @@ public class MountTableStoreImpl extends MountTableStore {
     AddMountTableEntryResponse response =
         AddMountTableEntryResponse.newInstance();
     response.setStatus(status);
+    updateCacheAllRouters();
     return response;
   }
 
@@ -86,6 +89,7 @@ public class MountTableStoreImpl extends MountTableStore {
     UpdateMountTableEntryResponse response =
         UpdateMountTableEntryResponse.newInstance();
     response.setStatus(status);
+    updateCacheAllRouters();
     return response;
   }
 
@@ -110,6 +114,7 @@ public class MountTableStoreImpl extends MountTableStore {
     RemoveMountTableEntryResponse response =
         RemoveMountTableEntryResponse.newInstance();
     response.setStatus(status);
+    updateCacheAllRouters();
     return response;
   }
 
@@ -151,4 +156,17 @@ public class MountTableStoreImpl extends MountTableStore {
     response.setTimestamp(Time.now());
     return response;
   }
+
+  @Override
+  public RefreshMountTableEntriesResponse refreshMountTableEntries(
+      RefreshMountTableEntriesRequest request) throws IOException {
+    // Because this refresh is done through admin API, it should always be force
+    // refresh.
+    boolean result = loadCache(true);
+    RefreshMountTableEntriesResponse response =
+        RefreshMountTableEntriesResponse.newInstance();
+    response.setResult(result);
+    return response;
+  }
+
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/RefreshMountTableEntriesRequest.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.hadoop.hdfs.server.federation.store.protocol;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+
+/**
+ * API request for refreshing mount table cached entries from state store.
+ */
+public abstract class RefreshMountTableEntriesRequest {
+
+  public static RefreshMountTableEntriesRequest newInstance()
+      throws IOException {
+    return StateStoreSerializer
+        .newRecord(RefreshMountTableEntriesRequest.class);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/RefreshMountTableEntriesResponse.java

@@ -0,0 +1,44 @@
+/**
+ * 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.hdfs.server.federation.store.protocol;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience.Public;
+import org.apache.hadoop.classification.InterfaceStability.Unstable;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+
+/**
+ * API response for refreshing mount table entries cache from state store.
+ */
+public abstract class RefreshMountTableEntriesResponse {
+
+  public static RefreshMountTableEntriesResponse newInstance()
+      throws IOException {
+    return StateStoreSerializer
+        .newRecord(RefreshMountTableEntriesResponse.class);
+  }
+
+  @Public
+  @Unstable
+  public abstract boolean getResult();
+
+  @Public
+  @Unstable
+  public abstract void setResult(boolean result);
+}

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/RefreshMountTableEntriesRequestPBImpl.java

@@ -0,0 +1,67 @@
+/**
+ * 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.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RefreshMountTableEntriesRequestProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RefreshMountTableEntriesRequestProto.Builder;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RefreshMountTableEntriesRequestProtoOrBuilder;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.PBRecord;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the state store API object
+ * RefreshMountTableEntriesRequest.
+ */
+public class RefreshMountTableEntriesRequestPBImpl
+    extends RefreshMountTableEntriesRequest implements PBRecord {
+
+  private FederationProtocolPBTranslator<RefreshMountTableEntriesRequestProto,
+      Builder, RefreshMountTableEntriesRequestProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<>(
+              RefreshMountTableEntriesRequestProto.class);
+
+  public RefreshMountTableEntriesRequestPBImpl() {
+  }
+
+  public RefreshMountTableEntriesRequestPBImpl(
+      RefreshMountTableEntriesRequestProto proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public RefreshMountTableEntriesRequestProto getProto() {
+    // if builder is null build() returns null, calling getBuilder() to
+    // instantiate builder
+    this.translator.getBuilder();
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/RefreshMountTableEntriesResponsePBImpl.java

@@ -0,0 +1,74 @@
+/**
+ * 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.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RefreshMountTableEntriesResponseProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RefreshMountTableEntriesResponseProto.Builder;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.RefreshMountTableEntriesResponseProtoOrBuilder;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesResponse;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.PBRecord;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the state store API object
+ * RefreshMountTableEntriesResponse.
+ */
+public class RefreshMountTableEntriesResponsePBImpl
+    extends RefreshMountTableEntriesResponse implements PBRecord {
+
+  private FederationProtocolPBTranslator<RefreshMountTableEntriesResponseProto,
+      Builder, RefreshMountTableEntriesResponseProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<>(
+              RefreshMountTableEntriesResponseProto.class);
+
+  public RefreshMountTableEntriesResponsePBImpl() {
+  }
+
+  public RefreshMountTableEntriesResponsePBImpl(
+      RefreshMountTableEntriesResponseProto proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public RefreshMountTableEntriesResponseProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+
+  @Override
+  public boolean getResult() {
+    return this.translator.getProtoOrBuilder().getResult();
+  };
+
+  @Override
+  public void setResult(boolean result) {
+    this.translator.getBuilder().setResult(result);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/records/RouterState.java

@@ -88,6 +88,10 @@ public abstract class RouterState extends BaseRecord {
 
   public abstract long getDateStarted();
 
+  public abstract void setAdminAddress(String adminAddress);
+
+  public abstract String getAdminAddress();
+
   /**
    * Get the identifier for the Router. It uses the address.
    *

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/records/impl/pb/RouterStatePBImpl.java

@@ -199,4 +199,14 @@ public class RouterStatePBImpl extends RouterState implements PBRecord {
   public long getDateCreated() {
     return this.translator.getProtoOrBuilder().getDateCreated();
   }
+
+  @Override
+  public void setAdminAddress(String adminAddress) {
+    this.translator.getBuilder().setAdminAddress(adminAddress);
+  }
+
+  @Override
+  public String getAdminAddress() {
+    return this.translator.getProtoOrBuilder().getAdminAddress();
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/tools/federation/RouterAdmin.java

@@ -54,6 +54,8 @@ import org.apache.hadoop.hdfs.server.federation.store.protocol.GetSafeModeReques
 import org.apache.hadoop.hdfs.server.federation.store.protocol.GetSafeModeResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.LeaveSafeModeRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.LeaveSafeModeResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryRequest;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryResponse;
 import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateMountTableEntryRequest;
@@ -107,7 +109,8 @@ public class RouterAdmin extends Configured implements Tool {
     if (cmd == null) {
       String[] commands =
           {"-add", "-update", "-rm", "-ls", "-setQuota", "-clrQuota",
-              "-safemode", "-nameservice", "-getDisabledNameservices"};
+              "-safemode", "-nameservice", "-getDisabledNameservices",
+              "-refresh"};
       StringBuilder usage = new StringBuilder();
       usage.append("Usage: hdfs dfsrouteradmin :\n");
       for (int i = 0; i < commands.length; i++) {
@@ -142,6 +145,8 @@ public class RouterAdmin extends Configured implements Tool {
       return "\t[-nameservice enable | disable <nameservice>]";
     } else if (cmd.equals("-getDisabledNameservices")) {
       return "\t[-getDisabledNameservices]";
+    } else if (cmd.equals("-refresh")) {
+      return "\t[-refresh]";
     }
     return getUsage(null);
   }
@@ -230,9 +235,10 @@ public class RouterAdmin extends Configured implements Tool {
       printUsage(cmd);
       return exitCode;
     }
+    String address = null;
     // Initialize RouterClient
     try {
-      String address = getConf().getTrimmed(
+      address = getConf().getTrimmed(
           RBFConfigKeys.DFS_ROUTER_ADMIN_ADDRESS_KEY,
           RBFConfigKeys.DFS_ROUTER_ADMIN_ADDRESS_DEFAULT);
       InetSocketAddress routerSocket = NetUtils.createSocketAddr(address);
@@ -302,6 +308,8 @@ public class RouterAdmin extends Configured implements Tool {
         manageNameservice(subcmd, nsId);
       } else if ("-getDisabledNameservices".equals(cmd)) {
         getDisabledNameservices();
+      } else if ("-refresh".equals(cmd)) {
+        refresh(address);
       } else {
         throw new IllegalArgumentException("Unknown Command: " + cmd);
       }
@@ -337,6 +345,27 @@ public class RouterAdmin extends Configured implements Tool {
     return exitCode;
   }
 
+  private void refresh(String address) throws IOException {
+    if (refreshRouterCache()) {
+      System.out.println(
+          "Successfully updated mount table cache on router " + address);
+    }
+  }
+
+  /**
+   * Refresh mount table cache on connected router.
+   *
+   * @return true if cache refreshed successfully
+   * @throws IOException
+   */
+  private boolean refreshRouterCache() throws IOException {
+    RefreshMountTableEntriesResponse response =
+        client.getMountTableManager().refreshMountTableEntries(
+            RefreshMountTableEntriesRequest.newInstance());
+    return response.getResult();
+  }
+
+
   /**
    * Add a mount table entry or update if it exists.
    *

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/proto/FederationProtocol.proto

@@ -193,6 +193,7 @@ message RouterRecordProto {
   optional string version = 6;
   optional string compileInfo = 7;
   optional uint64 dateStarted = 8;
+  optional string adminAddress = 9;
 }
 
 message GetRouterRegistrationRequestProto {
@@ -219,6 +220,13 @@ message RouterHeartbeatResponseProto {
   optional bool status = 1;
 }
 
+message RefreshMountTableEntriesRequestProto {
+}
+
+message RefreshMountTableEntriesResponseProto {
+  optional bool result = 1;
+}
+
 /////////////////////////////////////////////////
 // Route State
 /////////////////////////////////////////////////

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/proto/RouterProtocol.proto

@@ -74,4 +74,9 @@ service RouterAdminProtocolService {
    * Get the list of disabled name services.
    */
   rpc getDisabledNameservices(GetDisabledNameservicesRequestProto) returns (GetDisabledNameservicesResponseProto);
+
+  /**
+   * Refresh mount entries
+   */
+  rpc refreshMountTableEntries(RefreshMountTableEntriesRequestProto) returns(RefreshMountTableEntriesResponseProto);
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/resources/hdfs-rbf-default.xml

@@ -547,4 +547,38 @@
     </description>
   </property>
 
+  <property>
+    <name>dfs.federation.router.mount-table.cache.update</name>
+    <value>false</value>
+    <description>Set true to enable MountTableRefreshService. This service
+      updates mount table cache immediately after adding, modifying or
+      deleting the mount table entries. If this service is not enabled
+      mount table cache are refreshed periodically by
+      StateStoreCacheUpdateService
+    </description>
+  </property>
+
+  <property>
+    <name>dfs.federation.router.mount-table.cache.update.timeout</name>
+    <value>1m</value>
+    <description>This property defines how long to wait for all the
+      admin servers to finish their mount table cache update. This setting
+      supports multiple time unit suffixes as described in
+      dfs.federation.router.safemode.extension.
+    </description>
+  </property>
+
+  <property>
+    <name>dfs.federation.router.mount-table.cache.update.client.max.time
+    </name>
+    <value>5m</value>
+    <description>Remote router mount table cache is updated through
+      RouterClient(RPC call). To improve performance, RouterClient
+      connections are cached but it should not be kept in cache forever.
+      This property defines the max time a connection can be cached. This
+      setting supports multiple time unit suffixes as described in
+      dfs.federation.router.safemode.extension.
+    </description>
+  </property>
+
 </configuration>

hadoop-hdfs-project/hadoop-hdfs-rbf/src/site/markdown/HDFSRouterFederation.md

@@ -230,6 +230,12 @@ Ls command will show below information for each mount table entry:
     Source                    Destinations              Owner                     Group                     Mode                      Quota/Usage
     /path                     ns0->/path                root                      supergroup                rwxr-xr-x                 [NsQuota: 50/0, SsQuota: 100 B/0 B]
 
+Mount table cache is refreshed periodically but it can also be refreshed by executing refresh command:
+
+    [hdfs]$ $HADOOP_HOME/bin/hdfs dfsrouteradmin -refresh
+
+The above command will refresh cache of the connected router. This command is redundant when mount table refresh service is enabled as the service will always keep the cache updated.
+
 #### Multiple subclusters
 A mount point also supports mapping multiple subclusters.
 For example, to create a mount point that stores files in subclusters `ns1` and `ns2`.
@@ -380,6 +386,9 @@ The connection to the State Store and the internal caching at the Router.
 | dfs.federation.router.store.connection.test | 60000 | How often to check for the connection to the State Store in milliseconds. |
 | dfs.federation.router.cache.ttl | 60000 | How often to refresh the State Store caches in milliseconds. |
 | dfs.federation.router.store.membership.expiration | 300000 | Expiration time in milliseconds for a membership record. |
+| dfs.federation.router.mount-table.cache.update | false | If true, Mount table cache is updated whenever a mount table entry is added, modified or removed for all the routers. |
+| dfs.federation.router.mount-table.cache.update.timeout | 1m | Max time to wait for all the routers to finish their mount table cache update. |
+| dfs.federation.router.mount-table.cache.update.client.max.time | 5m | Max time a RouterClient connection can be cached. |
 
 ### Routing
 

hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/FederationTestUtils.java

@@ -56,6 +56,8 @@ import org.apache.hadoop.hdfs.server.namenode.FSNamesystem;
 import org.apache.hadoop.hdfs.server.namenode.NameNode;
 import org.apache.hadoop.hdfs.server.namenode.NameNode.OperationCategory;
 import org.apache.hadoop.hdfs.server.namenode.ha.HAContext;
+import org.apache.hadoop.hdfs.server.federation.store.RouterStore;
+import org.apache.hadoop.hdfs.server.federation.store.records.RouterState;
 import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
 import org.apache.hadoop.security.AccessControlException;
 import org.apache.hadoop.test.GenericTestUtils;
@@ -316,4 +318,29 @@ public final class FederationTestUtils {
     }).when(spyHAContext).checkOperation(any(OperationCategory.class));
     Whitebox.setInternalState(namesystem, "haContext", spyHAContext);
   }
+
+  /**
+   * Wait for a number of routers to be registered in state store.
+   *
+   * @param stateManager number of routers to be registered.
+   * @param routerCount number of routers to be registered.
+   * @param tiemout max wait time in ms
+   */
+  public static void waitRouterRegistered(RouterStore stateManager,
+      long routerCount, int timeout) throws Exception {
+    GenericTestUtils.waitFor(new Supplier<Boolean>() {
+      @Override
+      public Boolean get() {
+        try {
+          List<RouterState> cachedRecords = stateManager.getCachedRecords();
+          if (cachedRecords.size() == routerCount) {
+            return true;
+          }
+        } catch (IOException e) {
+          // Ignore
+        }
+        return false;
+      }
+    }, 100, timeout);
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/RouterConfigBuilder.java

@@ -38,6 +38,7 @@ public class RouterConfigBuilder {
   private boolean enableMetrics = false;
   private boolean enableQuota = false;
   private boolean enableSafemode = false;
+  private boolean enableCacheRefresh;
 
   public RouterConfigBuilder(Configuration configuration) {
     this.conf = configuration;
@@ -104,6 +105,11 @@ public class RouterConfigBuilder {
     return this;
   }
 
+  public RouterConfigBuilder refreshCache(boolean enable) {
+    this.enableCacheRefresh = enable;
+    return this;
+  }
+
   public RouterConfigBuilder rpc() {
     return this.rpc(true);
   }
@@ -140,6 +146,10 @@ public class RouterConfigBuilder {
     return this.safemode(true);
   }
 
+  public RouterConfigBuilder refreshCache() {
+    return this.refreshCache(true);
+  }
+
   public Configuration build() {
     conf.setBoolean(RBFConfigKeys.DFS_ROUTER_STORE_ENABLE,
         this.enableStateStore);
@@ -158,6 +168,8 @@ public class RouterConfigBuilder {
         this.enableQuota);
     conf.setBoolean(RBFConfigKeys.DFS_ROUTER_SAFEMODE_ENABLE,
         this.enableSafemode);
+    conf.setBoolean(RBFConfigKeys.MOUNT_TABLE_CACHE_UPDATE,
+        this.enableCacheRefresh);
     return conf;
   }
 }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/router/TestRouterAdminCLI.java

@@ -799,6 +799,28 @@ public class TestRouterAdminCLI {
     assertTrue(err.toString().contains("No arguments allowed"));
   }
 
+  @Test
+  public void testRefreshMountTableCache() throws Exception {
+    String src = "/refreshMount";
+
+    // create mount table entry
+    String[] argv = new String[] {"-add", src, "refreshNS0", "/refreshDest"};
+    assertEquals(0, ToolRunner.run(admin, argv));
+
+    // refresh the mount table entry cache
+    System.setOut(new PrintStream(out));
+    argv = new String[] {"-refresh"};
+    assertEquals(0, ToolRunner.run(admin, argv));
+    assertTrue(
+        out.toString().startsWith("Successfully updated mount table cache"));
+
+    // Now ls should return that mount table entry
+    out.reset();
+    argv = new String[] {"-ls", src};
+    assertEquals(0, ToolRunner.run(admin, argv));
+    assertTrue(out.toString().contains(src));
+  }
+
   /**
    * Wait for the Router transforming to expected state.
    * @param expectedState Expected Router state.
@@ -836,8 +858,7 @@ public class TestRouterAdminCLI {
   }
 
   @Test
-  public void testUpdateDestinationForExistingMountTable() throws
-  Exception {
+  public void testUpdateDestinationForExistingMountTable() throws Exception {
     // Add a mount table firstly
     String nsId = "ns0";
     String src = "/test-updateDestinationForExistingMountTable";

hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/router/TestRouterMountTableCacheRefresh.java

@@ -0,0 +1,396 @@
+/**
+ * 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.hdfs.server.federation.router;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.apache.curator.test.TestingServer;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeys;
+import org.apache.hadoop.hdfs.server.federation.FederationTestUtils;
+import org.apache.hadoop.hdfs.server.federation.MiniRouterDFSCluster;
+import org.apache.hadoop.hdfs.server.federation.MiniRouterDFSCluster.RouterContext;
+import org.apache.hadoop.hdfs.server.federation.RouterConfigBuilder;
+import org.apache.hadoop.hdfs.server.federation.resolver.FileSubclusterResolver;
+import org.apache.hadoop.hdfs.server.federation.resolver.MountTableManager;
+import org.apache.hadoop.hdfs.server.federation.store.RouterStore;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.AddMountTableEntryRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.AddMountTableEntryResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RefreshMountTableEntriesResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.RemoveMountTableEntryResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateMountTableEntryRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateMountTableEntryResponse;
+import org.apache.hadoop.hdfs.server.federation.store.records.MountTable;
+import org.apache.hadoop.service.Service.STATE;
+import org.apache.hadoop.test.GenericTestUtils;
+import org.apache.hadoop.util.Time;
+import org.junit.After;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+/**
+ * This test class verifies that mount table cache is updated on all the routers
+ * when MountTableRefreshService is enabled and there is a change in mount table
+ * entries.
+ */
+public class TestRouterMountTableCacheRefresh {
+  private static TestingServer curatorTestingServer;
+  private static MiniRouterDFSCluster cluster;
+  private static RouterContext routerContext;
+  private static MountTableManager mountTableManager;
+
+  @BeforeClass
+  public static void setUp() throws Exception {
+    curatorTestingServer = new TestingServer();
+    curatorTestingServer.start();
+    final String connectString = curatorTestingServer.getConnectString();
+    int numNameservices = 2;
+    cluster = new MiniRouterDFSCluster(false, numNameservices);
+    Configuration conf = new RouterConfigBuilder().refreshCache().admin().rpc()
+        .heartbeat().build();
+    conf.setClass(RBFConfigKeys.FEDERATION_FILE_RESOLVER_CLIENT_CLASS,
+        RBFConfigKeys.FEDERATION_FILE_RESOLVER_CLIENT_CLASS_DEFAULT,
+        FileSubclusterResolver.class);
+    conf.set(CommonConfigurationKeys.ZK_ADDRESS, connectString);
+    conf.setBoolean(RBFConfigKeys.DFS_ROUTER_STORE_ENABLE, true);
+    cluster.addRouterOverrides(conf);
+    cluster.startCluster();
+    cluster.startRouters();
+    cluster.waitClusterUp();
+    routerContext = cluster.getRandomRouter();
+    RouterStore routerStateManager =
+        routerContext.getRouter().getRouterStateManager();
+    mountTableManager = routerContext.getAdminClient().getMountTableManager();
+    // wait for one minute for all the routers to get registered
+    FederationTestUtils.waitRouterRegistered(routerStateManager,
+        numNameservices, 60000);
+  }
+
+  @AfterClass
+  public static void destory() {
+    try {
+      curatorTestingServer.close();
+      cluster.shutdown();
+    } catch (IOException e) {
+      // do nothing
+    }
+  }
+
+  @After
+  public void tearDown() throws IOException {
+    clearEntries();
+  }
+
+  private void clearEntries() throws IOException {
+    List<MountTable> result = getMountTableEntries();
+    for (MountTable mountTable : result) {
+      RemoveMountTableEntryResponse removeMountTableEntry =
+          mountTableManager.removeMountTableEntry(RemoveMountTableEntryRequest
+              .newInstance(mountTable.getSourcePath()));
+      assertTrue(removeMountTableEntry.getStatus());
+    }
+  }
+
+  /**
+   * addMountTableEntry API should internally update the cache on all the
+   * routers.
+   */
+  @Test
+  public void testMountTableEntriesCacheUpdatedAfterAddAPICall()
+      throws IOException {
+
+    // Existing mount table size
+    int existingEntriesCount = getNumMountTableEntries();
+    String srcPath = "/addPath";
+    MountTable newEntry = MountTable.newInstance(srcPath,
+        Collections.singletonMap("ns0", "/addPathDest"), Time.now(),
+        Time.now());
+    addMountTableEntry(mountTableManager, newEntry);
+
+    // When Add entry is done, all the routers must have updated its mount table
+    // entry
+    List<RouterContext> routers = getRouters();
+    for (RouterContext rc : routers) {
+      List<MountTable> result =
+          getMountTableEntries(rc.getAdminClient().getMountTableManager());
+      assertEquals(1 + existingEntriesCount, result.size());
+      MountTable mountTableResult = result.get(0);
+      assertEquals(srcPath, mountTableResult.getSourcePath());
+    }
+  }
+
+  /**
+   * removeMountTableEntry API should internally update the cache on all the
+   * routers.
+   */
+  @Test
+  public void testMountTableEntriesCacheUpdatedAfterRemoveAPICall()
+      throws IOException {
+    // add
+    String srcPath = "/removePathSrc";
+    MountTable newEntry = MountTable.newInstance(srcPath,
+        Collections.singletonMap("ns0", "/removePathDest"), Time.now(),
+        Time.now());
+    addMountTableEntry(mountTableManager, newEntry);
+    int addCount = getNumMountTableEntries();
+    assertEquals(1, addCount);
+
+    // remove
+    RemoveMountTableEntryResponse removeMountTableEntry =
+        mountTableManager.removeMountTableEntry(
+            RemoveMountTableEntryRequest.newInstance(srcPath));
+    assertTrue(removeMountTableEntry.getStatus());
+
+    int removeCount = getNumMountTableEntries();
+    assertEquals(addCount - 1, removeCount);
+  }
+
+  /**
+   * updateMountTableEntry API should internally update the cache on all the
+   * routers.
+   */
+  @Test
+  public void testMountTableEntriesCacheUpdatedAfterUpdateAPICall()
+      throws IOException {
+    // add
+    String srcPath = "/updatePathSrc";
+    MountTable newEntry = MountTable.newInstance(srcPath,
+        Collections.singletonMap("ns0", "/updatePathDest"), Time.now(),
+        Time.now());
+    addMountTableEntry(mountTableManager, newEntry);
+    int addCount = getNumMountTableEntries();
+    assertEquals(1, addCount);
+
+    // update
+    String key = "ns1";
+    String value = "/updatePathDest2";
+    MountTable upateEntry = MountTable.newInstance(srcPath,
+        Collections.singletonMap(key, value), Time.now(), Time.now());
+    UpdateMountTableEntryResponse updateMountTableEntry =
+        mountTableManager.updateMountTableEntry(
+            UpdateMountTableEntryRequest.newInstance(upateEntry));
+    assertTrue(updateMountTableEntry.getStatus());
+    MountTable updatedMountTable = getMountTableEntry(srcPath);
+    assertNotNull("Updated mount table entrty cannot be null",
+        updatedMountTable);
+    assertEquals(1, updatedMountTable.getDestinations().size());
+    assertEquals(key,
+        updatedMountTable.getDestinations().get(0).getNameserviceId());
+    assertEquals(value, updatedMountTable.getDestinations().get(0).getDest());
+  }
+
+  /**
+   * After caching RouterClient if router goes down, refresh should be
+   * successful on other available router. The router which is not running
+   * should be ignored.
+   */
+  @Test
+  public void testCachedRouterClientBehaviourAfterRouterStoped()
+      throws IOException {
+    String srcPath = "/addPathClientCache";
+    MountTable newEntry = MountTable.newInstance(srcPath,
+        Collections.singletonMap("ns0", "/addPathClientCacheDest"), Time.now(),
+        Time.now());
+    addMountTableEntry(mountTableManager, newEntry);
+
+    // When Add entry is done, all the routers must have updated its mount table
+    // entry
+    List<RouterContext> routers = getRouters();
+    for (RouterContext rc : routers) {
+      List<MountTable> result =
+          getMountTableEntries(rc.getAdminClient().getMountTableManager());
+      assertEquals(1, result.size());
+      MountTable mountTableResult = result.get(0);
+      assertEquals(srcPath, mountTableResult.getSourcePath());
+    }
+
+    // Lets stop one router
+    for (RouterContext rc : routers) {
+      InetSocketAddress adminServerAddress =
+          rc.getRouter().getAdminServerAddress();
+      if (!routerContext.getRouter().getAdminServerAddress()
+          .equals(adminServerAddress)) {
+        cluster.stopRouter(rc);
+        break;
+      }
+    }
+
+    srcPath = "/addPathClientCache2";
+    newEntry = MountTable.newInstance(srcPath,
+        Collections.singletonMap("ns0", "/addPathClientCacheDest2"), Time.now(),
+        Time.now());
+    addMountTableEntry(mountTableManager, newEntry);
+    for (RouterContext rc : getRouters()) {
+      List<MountTable> result =
+          getMountTableEntries(rc.getAdminClient().getMountTableManager());
+      assertEquals(2, result.size());
+    }
+  }
+
+  private List<RouterContext> getRouters() {
+    List<RouterContext> result = new ArrayList<>();
+    for (RouterContext rc : cluster.getRouters()) {
+      if (rc.getRouter().getServiceState() == STATE.STARTED) {
+        result.add(rc);
+      }
+    }
+    return result;
+  }
+
+  @Test
+  public void testRefreshMountTableEntriesAPI() throws IOException {
+    RefreshMountTableEntriesRequest request =
+        RefreshMountTableEntriesRequest.newInstance();
+    RefreshMountTableEntriesResponse refreshMountTableEntriesRes =
+        mountTableManager.refreshMountTableEntries(request);
+    // refresh should be successful
+    assertTrue(refreshMountTableEntriesRes.getResult());
+  }
+
+  /**
+   * Verify cache update timeouts when any of the router takes more time than
+   * the configured timeout period.
+   */
+  @Test(timeout = 10000)
+  public void testMountTableEntriesCacheUpdateTimeout() throws IOException {
+    // Resources will be closed when router is closed
+    @SuppressWarnings("resource")
+    MountTableRefresherService mountTableRefresherService =
+        new MountTableRefresherService(routerContext.getRouter()) {
+          @Override
+          protected MountTableRefresherThread getLocalRefresher(
+              String adminAddress) {
+            return new MountTableRefresherThread(null, adminAddress) {
+              @Override
+              public void run() {
+                try {
+                  // Sleep 1 minute
+                  Thread.sleep(60000);
+                } catch (InterruptedException e) {
+                  // Do nothing
+                }
+              }
+            };
+          }
+        };
+    Configuration config = routerContext.getRouter().getConfig();
+    config.setTimeDuration(RBFConfigKeys.MOUNT_TABLE_CACHE_UPDATE_TIMEOUT, 5,
+        TimeUnit.SECONDS);
+    mountTableRefresherService.init(config);
+    // One router is not responding for 1 minute, still refresh should
+    // finished in 5 second as cache update timeout is set 5 second.
+    mountTableRefresherService.refresh();
+    // Test case timeout is assert for this test case.
+  }
+
+  /**
+   * Verify Cached RouterClient connections are removed from cache and closed
+   * when their max live time is elapsed.
+   */
+  @Test
+  public void testRouterClientConnectionExpiration() throws Exception {
+    final AtomicInteger createCounter = new AtomicInteger();
+    final AtomicInteger removeCounter = new AtomicInteger();
+    // Resources will be closed when router is closed
+    @SuppressWarnings("resource")
+    MountTableRefresherService mountTableRefresherService =
+        new MountTableRefresherService(routerContext.getRouter()) {
+          @Override
+          protected void closeRouterClient(RouterClient client) {
+            super.closeRouterClient(client);
+            removeCounter.incrementAndGet();
+          }
+
+          @Override
+          protected RouterClient createRouterClient(
+              InetSocketAddress routerSocket, Configuration config)
+              throws IOException {
+            createCounter.incrementAndGet();
+            return super.createRouterClient(routerSocket, config);
+          }
+        };
+    int clientCacheTime = 2000;
+    Configuration config = routerContext.getRouter().getConfig();
+    config.setTimeDuration(
+        RBFConfigKeys.MOUNT_TABLE_CACHE_UPDATE_CLIENT_MAX_TIME, clientCacheTime,
+        TimeUnit.MILLISECONDS);
+    mountTableRefresherService.init(config);
+    // Do refresh to created RouterClient
+    mountTableRefresherService.refresh();
+    assertNotEquals("No RouterClient is created.", 0, createCounter.get());
+    /*
+     * Wait for clients to expire. Lets wait triple the cache eviction period.
+     * After cache eviction period all created client must be removed and
+     * closed.
+     */
+    GenericTestUtils.waitFor(() -> createCounter.get() == removeCounter.get(),
+        100, 3 * clientCacheTime);
+  }
+
+  private int getNumMountTableEntries() throws IOException {
+    List<MountTable> records = getMountTableEntries();
+    int oldEntriesCount = records.size();
+    return oldEntriesCount;
+  }
+
+  private MountTable getMountTableEntry(String srcPath) throws IOException {
+    List<MountTable> mountTableEntries = getMountTableEntries();
+    for (MountTable mountTable : mountTableEntries) {
+      String sourcePath = mountTable.getSourcePath();
+      if (srcPath.equals(sourcePath)) {
+        return mountTable;
+      }
+    }
+    return null;
+  }
+
+  private void addMountTableEntry(MountTableManager mountTableMgr,
+      MountTable newEntry) throws IOException {
+    AddMountTableEntryRequest addRequest =
+        AddMountTableEntryRequest.newInstance(newEntry);
+    AddMountTableEntryResponse addResponse =
+        mountTableMgr.addMountTableEntry(addRequest);
+    assertTrue(addResponse.getStatus());
+  }
+
+  private List<MountTable> getMountTableEntries() throws IOException {
+    return getMountTableEntries(mountTableManager);
+  }
+
+  private List<MountTable> getMountTableEntries(
+      MountTableManager mountTableManagerParam) throws IOException {
+    GetMountTableEntriesRequest request =
+        GetMountTableEntriesRequest.newInstance("/");
+    return mountTableManagerParam.getMountTableEntries(request).getEntries();
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSCommands.md

@@ -437,6 +437,7 @@ Usage:
           [-safemode enter | leave | get]
           [-nameservice disable | enable <nameservice>]
           [-getDisabledNameservices]
+          [-refresh]
 
 | COMMAND\_OPTION | Description |
 |:---- |:---- |
@@ -449,6 +450,7 @@ Usage:
 | `-safemode` `enter` `leave` `get` | Manually set the Router entering or leaving safe mode. The option *get* will be used for verifying if the Router is in safe mode state. |
 | `-nameservice` `disable` `enable` *nameservice* | Disable/enable  a name service from the federation. If disabled, requests will not go to that name service. |
 | `-getDisabledNameservices` | Get the name services that are disabled in the federation. |
+| `-refresh` | Update mount table cache of the connected router. |
 
 The commands for managing Router-based federation. See [Mount table management](../hadoop-hdfs-rbf/HDFSRouterFederation.html#Mount_table_management) for more info.