HDFS-13388. RequestHedgingProxyProvider calls multiple configured NNs all the time. Contributed by Jinglun.

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/RequestHedgingProxyProvider.java

@@ -79,6 +79,20 @@ public class RequestHedgingProxyProvider<T> extends
     public Object
     invoke(Object proxy, final Method method, final Object[] args)
             throws Throwable {
+      if (currentUsedProxy != null) {
+        try {
+          Object retVal = method.invoke(currentUsedProxy.proxy, args);
+          LOG.debug("Invocation successful on [{}]",
+              currentUsedProxy.proxyInfo);
+          return retVal;
+        } catch (InvocationTargetException ex) {
+          Exception unwrappedException = unwrapInvocationTargetException(ex);
+          logProxyException(unwrappedException, currentUsedProxy.proxyInfo);
+          LOG.trace("Unsuccessful invocation on [{}]",
+              currentUsedProxy.proxyInfo);
+          throw unwrappedException;
+        }
+      }
       Map<Future<Object>, ProxyInfo<T>> proxyMap = new HashMap<>();
       int numAttempts = 0;
 

hadoop-hdfs-project/hadoop-hdfs-client/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestRequestHedgingProxyProvider.java

@@ -43,10 +43,15 @@ import org.junit.Assert;
 import org.junit.Before;
 import org.junit.BeforeClass;
 import org.junit.Test;
+
+import static org.apache.hadoop.test.GenericTestUtils.assertExceptionContains;
+import static org.junit.Assert.assertEquals;
 import org.mockito.Matchers;
 import org.mockito.Mockito;
 import org.mockito.invocation.InvocationOnMock;
 import org.mockito.stubbing.Answer;
+import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.mock;
 
 import com.google.common.collect.Lists;
 
@@ -99,6 +104,80 @@ public class TestRequestHedgingProxyProvider {
     Mockito.verify(goodMock).getStats();
   }
 
+  @Test
+  public void testRequestNNAfterOneSuccess() throws Exception {
+    final AtomicInteger goodCount = new AtomicInteger(0);
+    final AtomicInteger badCount = new AtomicInteger(0);
+    final ClientProtocol goodMock = mock(ClientProtocol.class);
+    when(goodMock.getStats()).thenAnswer(new Answer<long[]>() {
+      @Override
+      public long[] answer(InvocationOnMock invocation) throws Throwable {
+        goodCount.incrementAndGet();
+        Thread.sleep(1000);
+        return new long[]{1};
+      }
+    });
+    final ClientProtocol badMock = mock(ClientProtocol.class);
+    when(badMock.getStats()).thenAnswer(new Answer<long[]>() {
+      @Override
+      public long[] answer(InvocationOnMock invocation) throws Throwable {
+        badCount.incrementAndGet();
+        throw new IOException("Bad mock !!");
+      }
+    });
+
+    RequestHedgingProxyProvider<ClientProtocol> provider =
+        new RequestHedgingProxyProvider<>(conf, nnUri, ClientProtocol.class,
+            createFactory(badMock, goodMock));
+    ClientProtocol proxy = provider.getProxy().proxy;
+    proxy.getStats();
+    assertEquals(1, goodCount.get());
+    assertEquals(1, badCount.get());
+    // We will only use the successful proxy after a successful invocation.
+    proxy.getStats();
+    assertEquals(2, goodCount.get());
+    assertEquals(1, badCount.get());
+  }
+
+  @Test
+  public void testExceptionInfo() throws Exception {
+    final ClientProtocol goodMock = mock(ClientProtocol.class);
+    when(goodMock.getStats()).thenAnswer(new Answer<long[]>() {
+      private boolean first = true;
+      @Override
+      public long[] answer(InvocationOnMock invocation)
+          throws Throwable {
+        if (first) {
+          Thread.sleep(1000);
+          first = false;
+          return new long[] {1};
+        } else {
+          throw new IOException("Expected Exception Info");
+        }
+      }
+    });
+    final ClientProtocol badMock = mock(ClientProtocol.class);
+    when(badMock.getStats()).thenAnswer(new Answer<long[]>() {
+      @Override
+      public long[] answer(InvocationOnMock invocation)
+          throws Throwable {
+        throw new IOException("Bad Mock! This is Standby!");
+      }
+    });
+
+    RequestHedgingProxyProvider<ClientProtocol> provider =
+        new RequestHedgingProxyProvider<>(conf, nnUri, ClientProtocol.class,
+            createFactory(badMock, goodMock));
+    ClientProtocol proxy = provider.getProxy().proxy;
+    proxy.getStats();
+    // Test getting the exception when the successful proxy encounters one.
+    try {
+      proxy.getStats();
+    } catch (IOException e) {
+      assertExceptionContains("Expected Exception Info", e);
+    }
+  }
+
   @Test
   public void testHedgingWhenOneIsSlow() throws Exception {
     final ClientProtocol goodMock = Mockito.mock(ClientProtocol.class);