HADOOP-14440. Add metrics for connections dropped. Contributed by Eric Badger.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Server.java

@@ -64,6 +64,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
 
 import javax.security.sasl.Sasl;
 import javax.security.sasl.SaslException;
@@ -1220,6 +1221,7 @@ void doAccept(SelectionKey key) throws InterruptedException, IOException,  OutOf
           if (channel.isOpen()) {
             IOUtils.cleanup(null, channel);
           }
+          connectionManager.droppedConnections.getAndIncrement();
           continue;
         }
         key.attach(c);  // so closeCurrentConnection can get the object
@@ -3160,6 +3162,16 @@ public String getNumOpenConnectionsPerUser() {
     return null;
   }
 
+  /**
+   * The number of RPC connections dropped due to
+   * too many connections.
+   * @return the number of dropped rpc connections
+   */
+  public long getNumDroppedConnections() {
+    return connectionManager.getDroppedConnections();
+
+  }
+
   /**
    * The number of rpc calls in the queue.
    * @return The number of rpc calls in the queue.
@@ -3277,7 +3289,8 @@ private static int channelIO(ReadableByteChannel readCh,
   }
   
   private class ConnectionManager {
-    final private AtomicInteger count = new AtomicInteger();    
+    final private AtomicInteger count = new AtomicInteger();
+    final private AtomicLong droppedConnections = new AtomicLong();
     final private Set<Connection> connections;
     /* Map to maintain the statistics per User */
     final private Map<String, Integer> userToConnectionsMap;
@@ -3364,6 +3377,11 @@ Map<String, Integer> getUserToConnectionsMap() {
       return userToConnectionsMap;
     }
 
+
+    long getDroppedConnections() {
+      return droppedConnections.get();
+    }
+
     int size() {
       return count.get();
     }

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/metrics/RpcMetrics.java

@@ -121,6 +121,10 @@ public String numOpenConnectionsPerUser() {
     return server.getCallQueueLen();
   }
 
+  @Metric("Number of dropped connections") public long numDroppedConnections() {
+    return server.getNumDroppedConnections();
+  }
+
   // Public instrumentation methods that could be extracted to an
   // abstract class if we decide to do custom instrumentation classes a la
   // JobTrackerInstrumentation. The methods with //@Override comment are

hadoop-common-project/hadoop-common/src/site/markdown/Metrics.md

@@ -79,6 +79,7 @@ Each metrics record contains tags such as Hostname and port (number to which ser
 | `RpcAuthorizationSuccesses` | Total number of authorization successes |
 | `NumOpenConnections` | Current number of open connections |
 | `CallQueueLength` | Current length of the call queue |
+| `numDroppedConnections` | Total number of dropped connections |
 | `rpcQueueTime`*num*`sNumOps` | Shows total number of RPC calls (*num* seconds granularity) if `rpc.metrics.quantile.enable` is set to true. *num* is specified by `rpc.metrics.percentiles.intervals`. |
 | `rpcQueueTime`*num*`s50thPercentileLatency` | Shows the 50th percentile of RPC queue time in milliseconds (*num* seconds granularity) if `rpc.metrics.quantile.enable` is set to true. *num* is specified by `rpc.metrics.percentiles.intervals`. |
 | `rpcQueueTime`*num*`s75thPercentileLatency` | Shows the 75th percentile of RPC queue time in milliseconds (*num* seconds granularity) if `rpc.metrics.quantile.enable` is set to true. *num* is specified by `rpc.metrics.percentiles.intervals`. |

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/ipc/TestIPC.java

@@ -1339,7 +1339,7 @@ public void run() {
 
   @Test
   public void testMaxConnections() throws Exception {
-    conf.setInt("ipc.server.max.connections", 5);
+    conf.setInt("ipc.server.max.connections", 6);
     Server server = null;
     Thread connectors[] = new Thread[10];
 
@@ -1374,8 +1374,10 @@ public void run() {
       }
 
       Thread.sleep(1000);
-      // server should only accept up to 5 connections
-      assertEquals(5, server.getNumOpenConnections());
+      // server should only accept up to 6 connections
+      assertEquals(6, server.getNumOpenConnections());
+      // server should drop the other 4 connections
+      assertEquals(4, server.getNumDroppedConnections());
 
       for (int i = 0; i < 10; i++) {
         connectors[i].join();