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https://issues.apache.org/jira/browse/HDFS-14657?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16893228#comment-16893228
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Konstantin Shvachko edited comment on HDFS-14657 at 7/26/19 12:29 AM:
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Hi [~zhangchen].
Looking at your patch v2. I am not sure I understand how your approach can
work. Suppose you release {{namesystem.writeUnlock()}} in
{{reportDiffSorted()}}, then somebody (unrelated to block report processing)
can modify blocks belonging to the storage, which invalidates
{{storageBlocksIterator}}, meaning calling {{next()}} will cause
{{ConcurrentModificationException}}.
was (Author: shv):
Hi [~zhangchen].
Looking at your patch v2. I am not sure I understand how your approach can
work. Suppose you release {{namesystem.writeUnlock()}} in
{{reportDiffSorted()}}, then somebody (unrelated to block report processing)
can modify blocks belonging to the storage, which will invalidates
{{storageBlocksIterator}}, meaning calling {{next()}} will cause
{{ConcurrentModificationException}}.
> Refine NameSystem lock usage during processing FBR
> --------------------------------------------------
>
> Key: HDFS-14657
> URL: https://issues.apache.org/jira/browse/HDFS-14657
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Chen Zhang
> Assignee: Chen Zhang
> Priority: Major
> Attachments: HDFS-14657-001.patch, HDFS-14657.002.patch
>
>
> The disk with 12TB capacity is very normal today, which means the FBR size is
> much larger than before, Namenode holds the NameSystemLock during processing
> block report for each storage, which might take quite a long time.
> On our production environment, processing large FBR usually cause a longer
> RPC queue time, which impacts client latency, so we did some simple work on
> refining the lock usage, which improved the p99 latency significantly.
> In our solution, BlockManager release the NameSystem write lock and request
> it again for every 5000 blocks(by default) during processing FBR, with the
> fair lock, all the RPC request can be processed before BlockManager
> re-acquire the write lock.
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