MAPREDUCE-6680. JHS UserLogDir scan algorithm sometime could skip directory with update in CloudFS (Azure FileSystem, S3, etc. Contributed by Junping Du

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-hs/src/main/java/org/apache/hadoop/mapreduce/v2/hs/HistoryFileManager.java

@@ -307,10 +307,21 @@ public class HistoryFileManager extends AbstractService {
    */
   private class UserLogDir {
     long modTime = 0;
-    
+    private long scanTime = 0;
+
     public synchronized void scanIfNeeded(FileStatus fs) {
       long newModTime = fs.getModificationTime();
-      if (modTime != newModTime) {
+      // MAPREDUCE-6680: In some Cloud FileSystem, like Azure FS or S3, file's
+      // modification time is truncated into seconds. In that case,
+      // modTime == newModTime doesn't means no file update in the directory,
+      // so we need to have additional check.
+      // Note: modTime (X second Y millisecond) could be casted to X second or
+      // X+1 second.
+      if (modTime != newModTime
+          || (scanTime/1000) == (modTime/1000)
+          || (scanTime/1000 + 1) == (modTime/1000)) {
+        // reset scanTime before scanning happens
+        scanTime = System.currentTimeMillis();
         Path p = fs.getPath();
         try {
           scanIntermediateDirectory(p);
@@ -324,10 +335,12 @@ public class HistoryFileManager extends AbstractService {
         if (LOG.isDebugEnabled()) {
           LOG.debug("Scan not needed of " + fs.getPath());
         }
+        // reset scanTime
+        scanTime = System.currentTimeMillis();
       }
     }
   }
-  
+
   public class HistoryFileInfo {
     private Path historyFile;
     private Path confFile;