HDFS-12813. RequestHedgingProxyProvider can hide Exception thrown from the Namenode for proxy size of 1. Contributed by Mukul Kumar Singh

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

@@ -18,6 +18,7 @@
 package org.apache.hadoop.hdfs.server.namenode.ha;
 
 import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
 import java.net.URI;
@@ -29,6 +30,7 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
+import java.util.concurrent.ExecutionException;
 
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.ipc.RemoteException;
@@ -87,9 +89,19 @@ public RequestHedgingInvocationHandler(
         targetProxies.remove(toIgnore);
         if (targetProxies.size() == 1) {
           ProxyInfo<T> proxyInfo = targetProxies.values().iterator().next();
+          try {
+            currentUsedProxy = proxyInfo;
             Object retVal = method.invoke(proxyInfo.proxy, args);
-          successfulProxy = proxyInfo;
+            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;
+          }
         }
         executor = Executors.newFixedThreadPool(proxies.size());
         completionService = new ExecutorCompletionService<>(executor);
@@ -112,15 +124,16 @@ public Object call() throws Exception {
           Future<Object> callResultFuture = completionService.take();
           Object retVal;
           try {
+            currentUsedProxy = proxyMap.get(callResultFuture);
             retVal = callResultFuture.get();
-            successfulProxy = proxyMap.get(callResultFuture);
             LOG.debug("Invocation successful on [{}]",
-                successfulProxy.proxyInfo);
+                currentUsedProxy.proxyInfo);
             return retVal;
-          } catch (Exception ex) {
+          } catch (ExecutionException ex) {
+            Exception unwrappedException = unwrapExecutionException(ex);
             ProxyInfo<T> tProxyInfo = proxyMap.get(callResultFuture);
-            logProxyException(ex, tProxyInfo.proxyInfo);
+            logProxyException(unwrappedException, tProxyInfo.proxyInfo);
-            badResults.put(tProxyInfo.proxyInfo, unwrapException(ex));
+            badResults.put(tProxyInfo.proxyInfo, unwrappedException);
             LOG.trace("Unsuccessful invocation on [{}]", tProxyInfo.proxyInfo);
             numAttempts--;
           }
@@ -143,7 +156,7 @@ public Object call() throws Exception {
   }
 
 
-  private volatile ProxyInfo<T> successfulProxy = null;
+  private volatile ProxyInfo<T> currentUsedProxy = null;
   private volatile String toIgnore = null;
 
   public RequestHedgingProxyProvider(Configuration conf, URI uri,
@@ -154,8 +167,8 @@ public RequestHedgingProxyProvider(Configuration conf, URI uri,
   @SuppressWarnings("unchecked")
   @Override
   public synchronized ProxyInfo<T> getProxy() {
-    if (successfulProxy != null) {
+    if (currentUsedProxy != null) {
-      return successfulProxy;
+      return currentUsedProxy;
     }
     Map<String, ProxyInfo<T>> targetProxyInfos = new HashMap<>();
     StringBuilder combinedInfo = new StringBuilder("[");
@@ -175,8 +188,8 @@ public synchronized ProxyInfo<T> getProxy() {
 
   @Override
   public synchronized void performFailover(T currentProxy) {
-    toIgnore = successfulProxy.proxyInfo;
+    toIgnore = this.currentUsedProxy.proxyInfo;
-    successfulProxy = null;
+    this.currentUsedProxy = null;
   }
 
   /**
@@ -187,19 +200,18 @@ public synchronized void performFailover(T currentProxy) {
    */
   private void logProxyException(Exception ex, String proxyInfo) {
     if (isStandbyException(ex)) {
-      LOG.debug("Invocation returned standby exception on [{}]", proxyInfo);
+      LOG.debug("Invocation returned standby exception on [{}]", proxyInfo, ex);
     } else {
-      LOG.warn("Invocation returned exception on [{}]", proxyInfo);
+      LOG.warn("Invocation returned exception on [{}]", proxyInfo, ex);
     }
   }
 
   /**
    * Check if the returned exception is caused by an standby namenode.
-   * @param ex Exception to check.
+   * @param exception Exception to check.
    * @return If the exception is caused by an standby namenode.
    */
-  private boolean isStandbyException(Exception ex) {
+  private boolean isStandbyException(Exception exception) {
-    Exception exception = unwrapException(ex);
     if (exception instanceof RemoteException) {
       return ((RemoteException) exception).unwrapRemoteException()
           instanceof StandbyException;
@@ -208,24 +220,43 @@ private boolean isStandbyException(Exception ex) {
   }
 
   /**
-   * Unwraps the exception. <p>
+   * Unwraps the ExecutionException. <p>
    * Example:
    * <blockquote><pre>
    * if ex is
-   * ExecutionException(InvocationTargetExeption(SomeException))
+   * ExecutionException(InvocationTargetException(SomeException))
    * returns SomeException
    * </pre></blockquote>
    *
    * @return unwrapped exception
    */
-  private Exception unwrapException(Exception ex) {
+  private Exception unwrapExecutionException(ExecutionException ex) {
+    if (ex != null) {
+      Throwable cause = ex.getCause();
+      if (cause instanceof InvocationTargetException) {
+        return
+            unwrapInvocationTargetException((InvocationTargetException)cause);
+      }
+    }
+    return ex;
+
+  }
+
+  /**
+   * Unwraps the InvocationTargetException. <p>
+   * Example:
+   * <blockquote><pre>
+   * if ex is InvocationTargetException(SomeException)
+   * returns SomeException
+   * </pre></blockquote>
+   *
+   * @return unwrapped exception
+   */
+  private Exception unwrapInvocationTargetException(
+      InvocationTargetException ex) {
     if (ex != null) {
       Throwable cause = ex.getCause();
       if (cause instanceof Exception) {
-        Throwable innerCause = cause.getCause();
-        if (innerCause instanceof Exception) {
-          return (Exception) innerCause;
-        }
         return (Exception) cause;
       }
     }

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

@@ -231,6 +231,64 @@ public long[] answer(InvocationOnMock invocation) throws Throwable {
     Assert.assertEquals(1, stats[0]);
   }
 
+  @Test
+  public void testFileNotFoundExceptionWithSingleProxy() throws Exception {
+    ClientProtocol active = Mockito.mock(ClientProtocol.class);
+    Mockito
+        .when(active.getBlockLocations(Matchers.anyString(),
+            Matchers.anyLong(), Matchers.anyLong()))
+        .thenThrow(new RemoteException("java.io.FileNotFoundException",
+            "File does not exist!"));
+
+    ClientProtocol standby = Mockito.mock(ClientProtocol.class);
+    Mockito
+        .when(standby.getBlockLocations(Matchers.anyString(),
+            Matchers.anyLong(), Matchers.anyLong()))
+        .thenThrow(
+            new RemoteException("org.apache.hadoop.ipc.StandbyException",
+                "Standby NameNode"));
+
+    RequestHedgingProxyProvider<ClientProtocol> provider =
+        new RequestHedgingProxyProvider<>(conf, nnUri,
+            ClientProtocol.class, createFactory(standby, active));
+    try {
+      provider.getProxy().proxy.getBlockLocations("/tmp/test.file", 0L, 20L);
+      Assert.fail("Should fail since the active namenode throws"
+          + " FileNotFoundException!");
+    } catch (MultiException me) {
+      for (Exception ex : me.getExceptions().values()) {
+        Exception rEx = ((RemoteException) ex).unwrapRemoteException();
+        if (rEx instanceof StandbyException) {
+          continue;
+        }
+        Assert.assertTrue(rEx instanceof FileNotFoundException);
+      }
+    }
+    //Perform failover now, there will only be one active proxy now
+    provider.performFailover(active);
+    try {
+      provider.getProxy().proxy.getBlockLocations("/tmp/test.file", 0L, 20L);
+      Assert.fail("Should fail since the active namenode throws"
+          + " FileNotFoundException!");
+    } catch (RemoteException ex) {
+      Exception rEx = ex.unwrapRemoteException();
+      if (rEx instanceof StandbyException) {
+        Mockito.verify(active).getBlockLocations(Matchers.anyString(),
+            Matchers.anyLong(), Matchers.anyLong());
+        Mockito.verify(standby, Mockito.times(2))
+            .getBlockLocations(Matchers.anyString(),
+            Matchers.anyLong(), Matchers.anyLong());
+      } else {
+        Assert.assertTrue(rEx instanceof FileNotFoundException);
+        Mockito.verify(active, Mockito.times(2))
+            .getBlockLocations(Matchers.anyString(),
+            Matchers.anyLong(), Matchers.anyLong());
+        Mockito.verify(standby).getBlockLocations(Matchers.anyString(),
+            Matchers.anyLong(), Matchers.anyLong());
+      }
+    }
+  }
+
   @Test
   public void testPerformFailoverWith3Proxies() throws Exception {
     conf.set(HdfsClientConfigKeys.DFS_HA_NAMENODES_KEY_PREFIX + "." + ns,