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https://issues.apache.org/jira/browse/HDFS-10966?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15685011#comment-15685011
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Kihwal Lee commented on HDFS-10966:
-----------------------------------
The 2.7 patch looks good.
> Enhance Dispatcher logic on deciding when to give up a source DataNode
> ----------------------------------------------------------------------
>
> Key: HDFS-10966
> URL: https://issues.apache.org/jira/browse/HDFS-10966
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: balancer & mover
> Reporter: Zhe Zhang
> Assignee: Mark Wagner
> Attachments: HDFS-10966-branch-2.7.00.patch, HDFS-10966.00.patch,
> HDFS-10966.01.patch
>
>
> When a {{Dispatcher}} thread works on a source DataNode, in each iteration it
> tries to execute a {{PendingMove}}. If no block is moved after 5 iterations,
> this source (over-utlized) DataNode is given up for this Balancer iteration
> (20 mins). This is problematic if the source DataNode was heavily loaded in
> the beginning of the iteration. It will quickly encounter 5 unsuccessful
> moves and be abandoned.
> We should enhance this logic by e.g. using elapsed time instead of number of
> iterations.
> {code}
> // Check if the previous move was successful
> } else {
> // source node cannot find a pending block to move, iteration +1
> noPendingMoveIteration++;
> // in case no blocks can be moved for source node's task,
> // jump out of while-loop after 5 iterations.
> if (noPendingMoveIteration >= MAX_NO_PENDING_MOVE_ITERATIONS) {
> LOG.info("Failed to find a pending move " +
> noPendingMoveIteration
> + " times. Skipping " + this);
> resetScheduledSize();
> }
> }
> {code}
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