HDFS-16698. Add a metric to sense possible MaxDirectoryItemsExceededException in time.

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/metrics/NamenodeBeanMetrics.java

@@ -781,6 +781,11 @@ public int getFsLockQueueLength() {
     return 0;
   }
 
+  @Override
+  public int getMaxDirectoryItemsAlarmNums() {
+    return 0;
+  }
+
   @Override
   public long getTotalSyncCount() {
     return 0;

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

@@ -83,6 +83,7 @@
 import java.util.TreeSet;
 import java.util.concurrent.ForkJoinPool;
 import java.util.concurrent.RecursiveAction;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import static org.apache.hadoop.fs.CommonConfigurationKeys.FS_PROTECTED_DIRECTORIES;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_ACCESSTIME_PRECISION_DEFAULT;
@@ -156,6 +157,8 @@ private static INodeDirectory createRoot(FSNamesystem namesystem) {
   private volatile boolean skipQuotaCheck = false; //skip while consuming edits
   private final int maxComponentLength;
   private final int maxDirItems;
+  private final int maxDirItemsAlarmThreshold;
+  private final AtomicInteger maxDirItemsAlarmNum;
   private final int lsLimit;  // max list limit
   private final int contentCountLimit; // max content summary counts per run
   private final long contentSleepMicroSec;
@@ -379,6 +382,8 @@ public enum DirOp {
     this.maxDirItems = conf.getInt(
         DFSConfigKeys.DFS_NAMENODE_MAX_DIRECTORY_ITEMS_KEY,
         DFSConfigKeys.DFS_NAMENODE_MAX_DIRECTORY_ITEMS_DEFAULT);
+    this.maxDirItemsAlarmThreshold = (int) Math.ceil(this.maxDirItems * 0.8);
+    this.maxDirItemsAlarmNum = new AtomicInteger(0);
     this.inodeXAttrsLimit = conf.getInt(
         DFSConfigKeys.DFS_NAMENODE_MAX_XATTRS_PER_INODE_KEY,
         DFSConfigKeys.DFS_NAMENODE_MAX_XATTRS_PER_INODE_DEFAULT);
@@ -1283,16 +1288,18 @@ void verifyMaxDirItems(INodeDirectory parent, String parentPath)
       throws MaxDirectoryItemsExceededException {
     final int count = parent.getChildrenList(CURRENT_STATE_ID).size();
     if (count >= maxDirItems) {
-      final MaxDirectoryItemsExceededException e
-          = new MaxDirectoryItemsExceededException(parentPath, maxDirItems,
-          count);
+      final MaxDirectoryItemsExceededException e = new MaxDirectoryItemsExceededException(
+          parentPath, maxDirItems, count);
       if (namesystem.isImageLoaded()) {
         throw e;
       } else {
         // Do not throw if edits log is still being processed
-        NameNode.LOG.error("FSDirectory.verifyMaxDirItems: "
-            + e.getLocalizedMessage());
+        NameNode.LOG.error("FSDirectory.verifyMaxDirItems: {}.", e.getLocalizedMessage());
       }
+    } else if (count >= maxDirItemsAlarmThreshold) {
+      LOG.warn("File count exceeding alarm threshold for {}: {}/{}",
+          parentPath, count, this.maxDirItems);
+      this.maxDirItemsAlarmNum.incrementAndGet();
     }
   }
 
@@ -1579,6 +1586,10 @@ long totalInodes() {
     return getInodeMapSize();
   }
 
+  int getMaxDirItemsAlarmNum() {
+    return this.maxDirItemsAlarmNum.get();
+  }
+
   /**
    * Reset the entire namespace tree.
    */

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

@@ -8888,6 +8888,17 @@ public long getTotalSyncCount() {
     return fsImage.editLog.getTotalSyncCount();
   }
 
+  /**
+   * Returns total number of alarms that SubDirectoryItems
+   * of one directory have reached alarm threshold.
+   */
+  @Override
+  @Metric({"MaxDirectoryItemsAlarmNums",
+      "Total number of alarms that SubDirectoryItems more than alarm threshold"})
+  public int getMaxDirectoryItemsAlarmNums() {
+    return this.dir.getMaxDirItemsAlarmNum();
+  }
+
   /**
    * Return total time spent doing sync operations on FSEditLog.
    */

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

@@ -224,6 +224,12 @@ public interface FSNamesystemMBean {
    */
   int getFsLockQueueLength();
 
+  /**
+   * Returns total number of alarms that SubDirectoryItems
+   * of one directory have reached alarm threshold.
+   */
+  public int getMaxDirectoryItemsAlarmNums();
+
   /**
    * Return total number of Sync Operations on FSEditLog.
    */

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

@@ -114,6 +114,26 @@ public void testMaxDirItems() throws Exception {
     mkdirs("/4444", MaxDirectoryItemsExceededException.class);
   }
 
+  @Test
+  public void testMaxDirItemsAlarm() throws Exception {
+    conf.setInt(DFSConfigKeys.DFS_NAMENODE_MAX_DIRECTORY_ITEMS_KEY, 10);
+    mkdirs("/1", null);
+    mkdirs("/22", null);
+    mkdirs("/333", null);
+    mkdirs("/4444", null);
+    mkdirs("/55555", null);
+    mkdirs("/666666", null);
+    mkdirs("/7777777", null);
+    mkdirs("/88888888", null);
+    assertEquals(0, fs.getMaxDirectoryItemsAlarmNums());
+    mkdirs("/999999999", null);
+    assertEquals(1, fs.getMaxDirectoryItemsAlarmNums());
+    mkdirs("/1010101010", null);
+    assertEquals(2, fs.getMaxDirectoryItemsAlarmNums());
+    mkdirs("/11111111111", MaxDirectoryItemsExceededException.class);
+    assertEquals(2, fs.getMaxDirectoryItemsAlarmNums());
+  }
+
   @Test
   public void testMaxDirItemsRename() throws Exception {
     conf.setInt(DFSConfigKeys.DFS_NAMENODE_MAX_DIRECTORY_ITEMS_KEY, 2);