HDFS-15096. RBF: GetServerDefaults Should be Cached At Router. Contributed by Ayush Saxena.

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

@@ -17,6 +17,8 @@
  */
 package org.apache.hadoop.hdfs.server.federation.router;
 
+import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_CLIENT_SERVER_DEFAULTS_VALIDITY_PERIOD_MS_DEFAULT;
+import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_CLIENT_SERVER_DEFAULTS_VALIDITY_PERIOD_MS_KEY;
 import static org.apache.hadoop.hdfs.server.federation.router.FederationUtil.updateMountPointStatus;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.crypto.CryptoProtocolVersion;
@@ -88,6 +90,7 @@ import org.apache.hadoop.io.Text;
 import org.apache.hadoop.net.ConnectTimeoutException;
 import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.security.token.Token;
+import org.apache.hadoop.util.Time;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -122,6 +125,15 @@ public class RouterClientProtocol implements ClientProtocol {
   private final FileSubclusterResolver subclusterResolver;
   private final ActiveNamenodeResolver namenodeResolver;
 
+  /**
+   * Caching server defaults so as to prevent redundant calls to namenode,
+   * similar to DFSClient, caching saves efforts when router connects
+   * to multiple clients.
+   */
+  private volatile FsServerDefaults serverDefaults;
+  private volatile long serverDefaultsLastUpdate;
+  private final long serverDefaultsValidityPeriod;
+
   /** If it requires response from all subclusters. */
   private final boolean allowPartialList;
   /** Time out when getting the mount statistics. */
@@ -155,7 +167,9 @@ public class RouterClientProtocol implements ClientProtocol {
         RBFConfigKeys.DFS_ROUTER_CLIENT_MOUNT_TIME_OUT,
         RBFConfigKeys.DFS_ROUTER_CLIENT_MOUNT_TIME_OUT_DEFAULT,
         TimeUnit.MILLISECONDS);
-
+    this.serverDefaultsValidityPeriod = conf.getLong(
+        DFS_CLIENT_SERVER_DEFAULTS_VALIDITY_PERIOD_MS_KEY,
+        DFS_CLIENT_SERVER_DEFAULTS_VALIDITY_PERIOD_MS_DEFAULT);
     // User and group for reporting
     try {
       this.superUser = UserGroupInformation.getCurrentUser().getShortUserName();
@@ -226,9 +240,15 @@ public class RouterClientProtocol implements ClientProtocol {
   @Override
   public FsServerDefaults getServerDefaults() throws IOException {
     rpcServer.checkOperation(NameNode.OperationCategory.READ);
-
-    RemoteMethod method = new RemoteMethod("getServerDefaults");
-    return rpcServer.invokeAtAvailableNs(method, FsServerDefaults.class);
+    long now = Time.monotonicNow();
+    if ((serverDefaults == null) || (now - serverDefaultsLastUpdate
+        > serverDefaultsValidityPeriod)) {
+      RemoteMethod method = new RemoteMethod("getServerDefaults");
+      serverDefaults =
+          rpcServer.invokeAtAvailableNs(method, FsServerDefaults.class);
+      serverDefaultsLastUpdate = now;
+    }
+    return serverDefaults;
   }
 
   @Override