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https://issues.apache.org/jira/browse/HDFS-16042?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17356692#comment-17356692
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Kihwal Lee commented on HDFS-16042:
-----------------------------------
It is not related to any incident. Since the default interval is 30 seconds,
the impact of the change will not be great, but still it is right thing to do.
If a lot of decommissioning and/or maintenance mode entering nodes are
introduced at once, the initial scan can last seconds. This initial scan is not
subject to the max blocks per iteration limit. By changing it from fixed
interval to fixed delay, such an impact will be dampened a bit in the long run.
The patch looks good.
> DatanodeAdminMonitor scan should be delay based
> -----------------------------------------------
>
> Key: HDFS-16042
> URL: https://issues.apache.org/jira/browse/HDFS-16042
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Ahmed Hussein
> Assignee: Ahmed Hussein
> Priority: Major
> Labels: pull-request-available
> Time Spent: 20m
> Remaining Estimate: 0h
>
> In {{DatanodeAdminManager.activate()}}, the Monitor task is scheduled with a
> fixed rate, ie. the period is from start1 -> start2.
> {code:java}
> executor.scheduleAtFixedRate(monitor, intervalSecs, intervalSecs,
> TimeUnit.SECONDS);
> {code}
> According to Java API docs for {{scheduleAtFixedRate}},
> {quote}If any execution of this task takes longer than its period, then
> subsequent executions may start late, but will not concurrently
> execute.{quote}
> It should be a fixed delay so it's end1 -> start1.
>
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