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https://issues.apache.org/jira/browse/HDFS-14657?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16892925#comment-16892925
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Chen Zhang commented on HDFS-14657:
-----------------------------------
Thanks [~jojochuang] for mentioning HADOOP-16452, also thanks [~hexiaoqiao] for
your explanation.
I guess Wei-Chiu mention that Jira for referring his comments there:
{quote}I am not so worried about block reports blocking NN lock. The block
report processing logic releases the NN lock every 4 milliseconds.
(BlockManager.BlockReportProcessingThread#processQueue)
{quote}
IIUC, the logic of release NN lock every 4 ms only works on batch processing
IBR, when process FBR, the thread will stuck for very long time if the FBR is
very huge
> 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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