HDFS-9533. seen_txid in the shared edits directory is modified during bootstrapping. Contributed by Kihwal Lee.

(cherry picked from commit 5cb1e0118b)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/BootstrapStandby.java
	hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestBootstrapStandby.java
(cherry picked from commit 3c0ae5914c)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -1629,6 +1629,9 @@ Release 2.7.3 - UNRELEASED
     HDFS-9516. Truncate file fails with data dirs on multiple disks.
     (Plamen Jeliazkov via shv)
 
+    HDFS-9533. seen_txid in the shared edits directory is modified during
+    bootstrapping (kihwal)
+
 Release 2.7.2 - UNRELEASED
 
   INCOMPATIBLE CHANGES

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

@@ -482,8 +482,24 @@ long getMostRecentCheckpointTime() {
    * @param txid the txid that has been reached
    */
   public void writeTransactionIdFileToStorage(long txid) {
+    writeTransactionIdFileToStorage(txid, null);
+  }
+
+  /**
+   * Write a small file in all available storage directories that
+   * indicates that the namespace has reached some given transaction ID.
+   *
+   * This is used when the image is loaded to avoid accidental rollbacks
+   * in the case where an edit log is fully deleted but there is no
+   * checkpoint. See TestNameEditsConfigs.testNameEditsConfigsFailure()
+   * @param txid the txid that has been reached
+   * @param type the type of directory
+   */
+  public void writeTransactionIdFileToStorage(long txid,
+      NameNodeDirType type) {
     // Write txid marker in all storage directories
-    for (StorageDirectory sd : storageDirs) {
+    for (Iterator<StorageDirectory> it = dirIterator(type); it.hasNext();) {
+      StorageDirectory sd = it.next();
       try {
         writeTransactionIdFile(sd, txid);
       } catch(IOException e) {

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

@@ -52,6 +52,7 @@
 import org.apache.hadoop.hdfs.server.namenode.FSNamesystem;
 import org.apache.hadoop.hdfs.server.namenode.NNStorage;
 import org.apache.hadoop.hdfs.server.namenode.NNStorage.NameNodeFile;
+import org.apache.hadoop.hdfs.server.namenode.NNStorage.NameNodeDirType;
 import org.apache.hadoop.hdfs.server.namenode.NNUpgradeUtil;
 import org.apache.hadoop.hdfs.server.namenode.NameNode;
 import org.apache.hadoop.hdfs.server.namenode.TransferFsImage;
@@ -313,13 +314,14 @@ private int downloadImage(NNStorage storage, NamenodeProtocol proxy)
         return ERR_CODE_LOGS_UNAVAILABLE;
       }
 
-      image.getStorage().writeTransactionIdFileToStorage(curTxId);
-
       // Download that checkpoint into our storage directories.
       MD5Hash hash = TransferFsImage.downloadImageToStorage(
           otherHttpAddr, imageTxId, storage, true, true);
       image.saveDigestAndRenameCheckpointImage(NameNodeFile.IMAGE, imageTxId,
           hash);
+
+      // Write seen_txid to the formatted image directories.
+      storage.writeTransactionIdFileToStorage(imageTxId, NameNodeDirType.IMAGE);
     } catch (IOException ioe) {
       throw ioe;
     } finally {

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

@@ -568,4 +568,11 @@ public static void assertNNFilesMatch(MiniDFSCluster cluster) throws Exception {
     FSImageTestUtil.assertParallelFilesAreIdentical(curDirs,
         ignoredFiles);
   }
+
+  public static long getStorageTxId(NameNode node, URI storageUri)
+      throws IOException {
+    StorageDirectory sDir = getFSImage(node).getStorage().
+        getStorageDirectory(storageUri);
+    return NNStorage.readTransactionIdFile(sDir);
+  }
 }

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

@@ -135,6 +135,13 @@ public void testDownloadingLaterCheckpoint() throws Exception {
       .getFSImage().getMostRecentCheckpointTxId();
     assertEquals(6, expectedCheckpointTxId);
 
+    // advance the current txid
+    cluster.getFileSystem(0).create(new Path("/test_txid"), (short)1).close();
+
+    // obtain the content of seen_txid
+    URI editsUri = cluster.getSharedEditsDir(0, 1);
+    long seen_txid_shared = FSImageTestUtil.getStorageTxId(nn0, editsUri);
+
     int rc = BootstrapStandby.run(
         new String[]{"-force"},
         cluster.getConfiguration(1));
@@ -145,6 +152,10 @@ public void testDownloadingLaterCheckpoint() throws Exception {
         ImmutableList.of((int)expectedCheckpointTxId));
     FSImageTestUtil.assertNNFilesMatch(cluster);
 
+    // Make sure the seen_txid was not modified by the standby
+    assertEquals(seen_txid_shared,
+        FSImageTestUtil.getStorageTxId(nn0, editsUri));
+
     // We should now be able to start the standby successfully.
     cluster.restartNameNode(1);
   }