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https://issues.apache.org/jira/browse/HDFS-14997?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16979453#comment-16979453
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Íñigo Goiri commented on HDFS-14997:
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We should add this to the metrics to be able to track if we are queueing too
many commands, etc.
Other minor comments:
* We should add a javadoc to the methods in CommandProcessingThread. Specially
to processQueue() evne though is private.
* For processQueue(), I prefer while instead of do/while.
* processQueue() should use {{numProcessCommands++}}. Let's also make it
{{numProcessedCommands}}.
* Do we need to do take and then poll?
* In the interrupted case, we should log with debug in the other cases (use
also the logger {} format). If it is interrupted, shouldn't shouldRun() return
false so no need to break?
* We should extend the CommandProcessingThread #enqueue() to support
{{List<DatanodeCommand>}} and {{DatanodeCommand}} as arguments so we don't need
to do the transformations in the part where we add it.
* {{processCommand(DatanodeCommand[] cmds)}} is kind of repeated now. Should we
merge the new and the old together?
> BPServiceActor process command from NameNode asynchronously
> -----------------------------------------------------------
>
> Key: HDFS-14997
> URL: https://issues.apache.org/jira/browse/HDFS-14997
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Reporter: Xiaoqiao He
> Assignee: Xiaoqiao He
> Priority: Major
> Attachments: HDFS-14997.001.patch, HDFS-14997.002.patch
>
>
> There are two core functions, report(#sendHeartbeat, #blockReport,
> #cacheReport) and #processCommand in #BPServiceActor main process flow. If
> processCommand cost long time it will block send report flow. Meanwhile
> processCommand could cost long time(over 1000s the worst case I meet) when IO
> load of DataNode is very high. Since some IO operations are under
> #datasetLock, So it has to wait to acquire #datasetLock long time when
> process some of commands(such as #DNA_INVALIDATE). In such case, #heartbeat
> will not send to NameNode in-time, and trigger other disasters.
> I propose to improve #processCommand asynchronously and not block
> #BPServiceActor to send heartbeat back to NameNode when meet high IO load.
> Notes:
> 1. Lifeline could be one effective solution, however some old branches are
> not support this feature.
> 2. IO operations under #datasetLock is another issue, I think we should solve
> it at another JIRA.
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