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https://issues.apache.org/jira/browse/HDFS-9543?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15255715#comment-15255715
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Anu Engineer commented on HDFS-9543:
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[~arpitagarwal] Thanks for the code review comments. I will post a revised
patch soon.
bq. I expect this situation will be seen only if the storage type of a disk
has changed since the planner generated the plan?
We allow disk balancer plans to be edited if needed. This prevents users from
making a mistake. We can avoid it but produces no harm. Please let me know if
you need this removed.
bq. That's a heavyweight lock to hold for the move. I don't think we should
synchronize on the Dataset.
Completely agree. I did this to play fair with DirectoryScanner. This lock is
being held by directoryScanner to prevent changes to blockMap. I wanted to make
sure that diskBalancer and DirectoryScanner play nicely. Please look at
{{DirectoryScanner#scan line 586}}. Please do let me know if this is not needed
in DiskBalancer.
bq. think computeDelay should substract the time taken for the move else the
computed delay will be too conservative. What do you think?
good catch. Thank you, I will fix this in next update.
bq. Precondition.checkState is redundant, subsequent lines will NPE if the
either object is null.
Agree and Precondition is going to throw somethign similar. But it does make
the invariant clear to the next person who is reading code instead of wondering
if I forgot to check a condition.
bq. I did not get this TODO. What does it mean to move blocks across block pools
I will make this comment clearer in the next update. Balancer supports a flag
called -blockpools -- HDFS-8890 seems to have added this. Just leaving a note
that we don't do this yet.
> DiskBalancer : Add Data mover
> ------------------------------
>
> Key: HDFS-9543
> URL: https://issues.apache.org/jira/browse/HDFS-9543
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode
> Reporter: Anu Engineer
> Assignee: Anu Engineer
> Attachments: HDFS-9543-HDFS-1312.001.patch
>
>
> This patch adds the actual mover logic to the datanode.
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