HDFS-14476. lock too long when fix inconsistent blocks between disk and in-memory. Contributed by Sean Chow.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DirectoryScanner.java

@@ -66,7 +66,7 @@ public class DirectoryScanner implements Runnable {
       LoggerFactory.getLogger(DirectoryScanner.class);
 
   private static final int DEFAULT_MAP_SIZE = 32768;
-
+  private static final int RECONCILE_BLOCKS_BATCH_SIZE = 1000;
   private final FsDatasetSpi<?> dataset;
   private final ExecutorService reportCompileThreadPool;
   private final ScheduledExecutorService masterThread;
@@ -424,10 +424,23 @@ public class DirectoryScanner implements Runnable {
    */
   @VisibleForTesting
   public void reconcile() throws IOException {
+    LOG.debug("reconcile start DirectoryScanning");
     scan();
 
+    // HDFS-14476: run checkAndUpadte with batch to avoid holding the lock too
+    // long
+    int loopCount = 0;
     for (final Map.Entry<String, ScanInfo> entry : diffs.getEntries()) {
       dataset.checkAndUpdate(entry.getKey(), entry.getValue());
+
+      if (loopCount % RECONCILE_BLOCKS_BATCH_SIZE == 0) {
+        try {
+          Thread.sleep(2000);
+        } catch (InterruptedException e) {
+          // do nothing
+        }
+      }
+      loopCount++;
     }
 
     if (!retainDiffs) {