HDFS-15099. [SBN Read] checkOperation(WRITE) should throw ObserverRetryOnActiveException for ObserverNode. Contributed by Chen Liang.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/retry/RetryPolicies.java

@@ -34,6 +34,7 @@
 
 import javax.security.sasl.SaslException;
 
+import org.apache.hadoop.ipc.ObserverRetryOnActiveException;
 import org.apache.hadoop.ipc.RemoteException;
 import org.apache.hadoop.ipc.RetriableException;
 import org.apache.hadoop.ipc.StandbyException;
@@ -678,7 +679,7 @@ public RetryAction shouldRetry(Exception e, int retries,
           e instanceof UnknownHostException ||
           e instanceof StandbyException ||
           e instanceof ConnectTimeoutException ||
-          isWrappedStandbyException(e)) {
+          shouldFailoverOnException(e)) {
         return new RetryAction(RetryAction.RetryDecision.FAILOVER_AND_RETRY,
             getFailoverOrRetrySleepTime(failovers));
       } else if (e instanceof RetriableException
@@ -730,12 +731,13 @@ private static long calculateExponentialTime(long time, int retries) {
     return calculateExponentialTime(time, retries, Long.MAX_VALUE);
   }
 
-  private static boolean isWrappedStandbyException(Exception e) {
+  private static boolean shouldFailoverOnException(Exception e) {
     if (!(e instanceof RemoteException)) {
       return false;
     }
     Exception unwrapped = ((RemoteException)e).unwrapRemoteException(
-        StandbyException.class);
+        StandbyException.class,
+        ObserverRetryOnActiveException.class);
     return unwrapped instanceof StandbyException;
   }
 

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

@@ -20,8 +20,6 @@
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 
-import java.io.IOException;
-
 /**
  * Thrown by a remote ObserverNode indicating the operation has failed and the
  * client should retry active namenode directly (instead of retry other
@@ -29,7 +27,7 @@
  */
 @InterfaceAudience.Private
 @InterfaceStability.Evolving
-public class ObserverRetryOnActiveException extends IOException {
+public class ObserverRetryOnActiveException extends StandbyException {
   static final long serialVersionUID = 1L;
   public ObserverRetryOnActiveException(String msg) {
     super(msg);

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

@@ -24,6 +24,7 @@
 import org.apache.hadoop.ha.HAServiceProtocol.HAServiceState;
 import org.apache.hadoop.hdfs.server.namenode.NameNode;
 import org.apache.hadoop.hdfs.server.namenode.NameNode.OperationCategory;
+import org.apache.hadoop.ipc.ObserverRetryOnActiveException;
 import org.apache.hadoop.ipc.StandbyException;
 
 /**
@@ -95,7 +96,17 @@ public void checkOperation(HAContext context, OperationCategory op)
     String faq = ". Visit https://s.apache.org/sbnn-error";
     String msg = "Operation category " + op + " is not supported in state "
         + context.getState() + faq;
-    throw new StandbyException(msg);
+    if (op == OperationCategory.WRITE && isObserver) {
+      // If observer receives a write call, return active retry
+      // exception to inform client to retry on active.
+      // A write should never happen on Observer. Except that,
+      // if access time is enabled. A open call can transition
+      // to a write operation. In this case, Observer
+      // should inform the client to retry this open on Active.
+      throw new ObserverRetryOnActiveException(msg);
+    } else {
+      throw new StandbyException(msg);
+    }
   }
 
   @Override

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

@@ -52,6 +52,7 @@
 import org.apache.hadoop.hdfs.server.namenode.NameNodeAdapter;
 import org.apache.hadoop.hdfs.server.namenode.TestFsck;
 import org.apache.hadoop.hdfs.tools.GetGroups;
+import org.apache.hadoop.ipc.ObserverRetryOnActiveException;
 import org.junit.After;
 import org.junit.AfterClass;
 import org.junit.Before;
@@ -366,6 +367,52 @@ public void testFsckWithObserver() throws Exception {
     assertTrue(result.contains("Status: HEALTHY"));
   }
 
+  /**
+   * Test that, if a write happens happens to go to Observer,
+   * Observer would throw {@link ObserverRetryOnActiveException},
+   * to inform client to retry on Active
+   *
+   * @throws Exception
+   */
+  @Test
+  public void testObserverRetryActiveException() throws Exception {
+    boolean thrownRetryException = false;
+    try {
+      // Force a write on Observer, which should throw
+      // retry on active exception.
+      dfsCluster.getNameNode(2)
+          .getRpcServer()
+          .mkdirs("/testActiveRetryException",
+              FsPermission.createImmutable((short) 0755), true);
+    } catch (ObserverRetryOnActiveException orae) {
+      thrownRetryException = true;
+    }
+    assertTrue(thrownRetryException);
+  }
+
+  /**
+   * Test that for open call, if access time update is required,
+   * the open call should go to active, instead of observer.
+   *
+   * @throws Exception
+   */
+  @Test
+  public void testAccessTimeUpdateRedirectToActive() throws Exception {
+    // Create a new pat to not mess up other tests
+    Path tmpTestPath = new Path("/TestObserverNodeAccessTime");
+    dfs.create(tmpTestPath, (short)1).close();
+    assertSentTo(0);
+    dfs.open(tmpTestPath).close();
+    assertSentTo(2);
+    // Set access time to a time in the far past.
+    // So that next read call is guaranteed to
+    // have passed access time period.
+    dfs.setTimes(tmpTestPath, 0, 0);
+    // Verify that aTime update redirects on Active
+    dfs.open(tmpTestPath).close();
+    assertSentTo(0);
+  }
+
   private void assertSentTo(int nnIdx) throws IOException {
     assertTrue("Request was not sent to the expected namenode " + nnIdx,
         HATestUtil.isSentToAnyOfNameNodes(dfs, dfsCluster, nnIdx));