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From "Uma Maheswara Rao G (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11164) Mover should avoid unnecessary retries if the block is pinned
Date Wed, 23 Nov 2016 22:02:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15691480#comment-15691480

Uma Maheswara Rao G commented on HDFS-11164:

[~rakeshr], Thanks for reporting the issue.
Adding extra error code make sense to me.

But the current patch may not solve for avoiding unnecessary retries issue I think.
Please check the following cases, correct me if I am wrong.

 // Check that the block movement failure(s) are only due to block pinning.
      // If yes, just mark as failed and exit without retries.
      if(!hasFailed && hasBlockPinningFailure){
        hasFailed = hasBlockPinningFailure;
      } else if (hasFailed && !hasSuccess) {
        if (retryCount.get() == retryMaxAttempts) {
          LOG.error("Failed to move some block's after "
              + retryMaxAttempts + " retries.");
          return result;
        } else {
      } else {
        // Reset retry count if no failure.
      return result;
Here !hasFailed && hasBlockPinningFailure case is targeting for only pinned failure
and no normal failures right? if so, when there are normal failures and pinned failures together,
it will still retry?
If it retries, it may scan that paths again and try to move even they are pinned blocks.
We may need to think this in a bit different way than node level failures I think.
One thought is, Failed blocks due to pinned can be stored separately and when retry happens
and if blocks exist in failedDueToPinned list, then skip to add them into PendingMoves? Just
a thought, we need to check the feasibility.

> Mover should avoid unnecessary retries if the block is pinned
> -------------------------------------------------------------
>                 Key: HDFS-11164
>                 URL: https://issues.apache.org/jira/browse/HDFS-11164
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: balancer & mover
>            Reporter: Rakesh R
>            Assignee: Rakesh R
>         Attachments: HDFS-11164-00.patch, HDFS-11164-01.patch
> When mover is trying to move a pinned block to another datanode, it will internally hits
the following IOException and mark the block movement as {{failure}}. Since the Mover has
{{dfs.mover.retry.max.attempts}} configs, it will continue moving this block until it reaches
{{retryMaxAttempts}}. If the block movement failure(s) are only due to block pinning, then
retry is unnecessary. The idea of this jira is to avoid retry attempts of pinned blocks as
they won't be able to move to a different node. 
> {code}
> 2016-11-22 10:56:10,537 WARN org.apache.hadoop.hdfs.server.balancer.Dispatcher: Failed
to move blk_1073741825_1001 with size=52 from to
> java.io.IOException: Got error, status=ERROR, status message opReplaceBlock BP-1772076264-
received exception java.io.IOException: Got error, status=ERROR, status message Not able to
copy block 1073741825 to / because it's pinned , copy block BP-1772076264-
from /, reportedBlock move is failed
> 	at org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtoUtil.checkBlockOpStatus(DataTransferProtoUtil.java:118)
> 	at org.apache.hadoop.hdfs.server.balancer.Dispatcher$PendingMove.receiveResponse(Dispatcher.java:417)
> 	at org.apache.hadoop.hdfs.server.balancer.Dispatcher$PendingMove.dispatch(Dispatcher.java:358)
> 	at org.apache.hadoop.hdfs.server.balancer.Dispatcher$PendingMove.access$5(Dispatcher.java:322)
> 	at org.apache.hadoop.hdfs.server.balancer.Dispatcher$1.run(Dispatcher.java:1075)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> 	at java.lang.Thread.run(Thread.java:745)
> {code}

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