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https://issues.apache.org/jira/browse/HDFS-7704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14318524#comment-14318524
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Zhe Zhang commented on HDFS-7704:
---------------------------------

[~kihwal] Trunk doesn't compile now. I quickly checked the commit log, it seems 
{{BPServiceActorAction.java}} is missing? It's in the patch though.

> DN heartbeat to Active NN may be blocked and expire if connection to Standby 
> NN continues to time out. 
> -------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-7704
>                 URL: https://issues.apache.org/jira/browse/HDFS-7704
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode, namenode
>    Affects Versions: 2.5.0
>            Reporter: Rushabh S Shah
>            Assignee: Rushabh S Shah
>             Fix For: 2.7.0
>
>         Attachments: HDFS-7704-v2.patch, HDFS-7704-v3.patch, 
> HDFS-7704-v4.patch, HDFS-7704-v5.patch, HDFS-7704.patch
>
>
> There are couple of synchronous calls in BPOfferservice (i.e reportBadBlocks 
> and trySendErrorReport) which will wait for both of the actor threads to 
> process this calls.
> This calls are made with writeLock acquired.
> When reportBadBlocks() is blocked at the RPC layer due to unreachable NN, 
> subsequent heartbeat response processing has to wait for the write lock. It 
> eventually gets through, but takes too long and it blocks the next heartbeat.
> In our HA cluster setup, the standby namenode was taking a long time to 
> process the request.
> Requesting improvement in datanode to make the above calls asynchronous since 
> these reports don't have any specific
> deadlines, so extra few seconds of delay should be acceptable.



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