[ 
https://issues.apache.org/jira/browse/HDFS-17068?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17741496#comment-17741496
 ] 

ASF GitHub Bot commented on HDFS-17068:
---------------------------------------

ayushtkn commented on code in PR #5809:
URL: https://github.com/apache/hadoop/pull/5809#discussion_r1257856998


##########
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/metrics/FSDatasetMBean.java:
##########
@@ -122,4 +122,9 @@ public interface FSDatasetMBean extends MetricsSource {
    * Returns the number of blocks that the datanode was unable to uncache
    */
   public long getNumBlocksFailedToUncache();
+
+  /**
+   * Returns the last time in milliseconds of directory scanner run.
+   */

Review Comment:
   can you change to
   ```
   Return the last time in milliseconds when the directory scanner successfully 
ran.
   ```



##########
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DirectoryScanner.java:
##########
@@ -487,6 +487,7 @@ public void reconcile() throws IOException {
     if (!retainDiffs) {
       clear();
     }
+    dataset.setLastDirScannerFinishTime(System.currentTimeMillis());

Review Comment:
   I think this should be done in the run the method after reconcile, from the 
correctness point of view
   ```
         reconcile();
         dataset.setLastDirScannerFinishTime(System.currentTimeMillis());
   ```



##########
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsDatasetSpi.java:
##########
@@ -692,4 +692,10 @@ ReplicaInfo moveBlockAcrossVolumes(final ExtendedBlock 
block,
    * Get the volume list.
    */
   List<FsVolumeImpl> getVolumeList();
+
+  /**
+   * Set the finish time of last directory scan.
+   * @param time

Review Comment:
   add description for the param, something like:
   ```
      * @param time the time when last directory scan finished successfully.
   ```



##########
hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalDatasetImpl.java:
##########
@@ -53,6 +53,7 @@ public class ExternalDatasetImpl implements 
FsDatasetSpi<ExternalVolumeImpl> {
   private final DatanodeStorage storage = new DatanodeStorage(
       DatanodeStorage.generateUuid(), DatanodeStorage.State.NORMAL,
       StorageType.DEFAULT);
+  private long lastDirScannerFinishTime;

Review Comment:
   unused?



##########
hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalDatasetImpl.java:
##########
@@ -477,4 +478,14 @@ public MountVolumeMap getMountVolumeMap() {
   public List<FsVolumeImpl> getVolumeList() {
     return null;
   }
+
+  @Override
+  public long getLastDirScannerFinishTime() {
+    return 0L;
+  }
+
+  @Override
+  public void setLastDirScannerFinishTime(long time) {
+
+  }

Review Comment:
   can we not have default empty implementation in the parent class, rather 
than implementing empty methods in child classes?





> Datanode should record last directory scan time.
> ------------------------------------------------
>
>                 Key: HDFS-17068
>                 URL: https://issues.apache.org/jira/browse/HDFS-17068
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: farmmamba
>            Assignee: farmmamba
>            Priority: Minor
>              Labels: pull-request-available
>
> I think it is useful for us to record last directory scan time for one 
> datanode. 



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