From e266a525fc3fabab83d91d11304ced95ab4beff9 Mon Sep 17 00:00:00 2001
From: gyz-web <76725986+gyz-web@users.noreply.github.com>
Date: Wed, 16 Apr 2025 21:21:24 +0800
Subject: [PATCH] HDFS-17769. Allows client to actively retry to Active
 NameNode when the Observer NameNode is too far behind client state id.

---
 .../server/namenode/GlobalStateIdContext.java |  7 +++---
 .../server/namenode/ha/TestObserverNode.java  | 25 +++++++++++++++++++
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/GlobalStateIdContext.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/GlobalStateIdContext.java
index 7d613594efd64..85397a273c62d 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/GlobalStateIdContext.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/GlobalStateIdContext.java
@@ -30,6 +30,7 @@
 import org.apache.hadoop.hdfs.server.namenode.ha.ObserverReadProxyProvider;
 import org.apache.hadoop.hdfs.server.namenode.ha.ReadOnly;
 import org.apache.hadoop.ipc.AlignmentContext;
+import org.apache.hadoop.ipc.ObserverRetryOnActiveException;
 import org.apache.hadoop.ipc.RetriableException;
 import org.apache.hadoop.ipc.StandbyException;
 import org.apache.hadoop.ipc.protobuf.RpcHeaderProtos.RpcRequestHeaderProto;
@@ -156,9 +157,9 @@ public long receiveRequestState(RpcRequestHeaderProto header,
         ESTIMATED_TRANSACTIONS_PER_SECOND
             * TimeUnit.MILLISECONDS.toSeconds(clientWaitTime)
             * ESTIMATED_SERVER_TIME_MULTIPLIER) {
-      throw new RetriableException(
-          "Observer Node is too far behind: serverStateId = "
-              + serverStateId + " clientStateId = " + clientStateId);
+      throw new ObserverRetryOnActiveException("Retrying to Active NameNode, Observer Node is too"
+          + " far behind: serverStateId = " + serverStateId
+          + " clientStateId = " + clientStateId);
     }
     return clientStateId;
   }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestObserverNode.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestObserverNode.java
index 55d17d3bb27c9..b27beb585dc87 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestObserverNode.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestObserverNode.java
@@ -518,6 +518,31 @@ public void testObserverRetryActiveException() throws Exception {
     assertTrue(thrownRetryException);
   }
 
+  /**
+   * Test that, when the server stateId is too far behind the
+   * client stateId, the request should be retried directly to
+   * Active NameNode, instead of constantly trying again.
+   */
+  @Test
+  public void testObserverRetryActiveExceptionWhenStateIdTooStale() throws Exception {
+    dfs.mkdir(testPath, FsPermission.getDefault());
+    assertSentTo(0);
+
+    // Set large stateId on the client，the server stateId is too far behind
+    // the client stateId and will retry to active.
+    long realStateId = HATestUtil.setACStateId(dfs, 1000000);
+    FileStatus fileStatus = dfs.getFileStatus(testPath);
+    assertNotNull(fileStatus);
+    assertSentTo(0);
+
+    // StateId restored to normal, request processed by observer.
+    HATestUtil.setACStateId(dfs, realStateId);
+    FileStatus fileStatus2= dfs.getFileStatus(testPath);
+    assertNotNull(fileStatus2);
+    assertSentTo(2);
+
+  }
+
   /**
    * Test that for open call, if access time update is required,
    * the open call should go to active, instead of observer.