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https://issues.apache.org/jira/browse/HDFS-7264?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14177248#comment-14177248
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Tsz Wo Nicholas Sze commented on HDFS-7264:
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Hi Vinay, thanks for reviewing the patch.
> Why can't heartbeat be enabled always.. without configuration flag, which is
> disabled by default. ?
It is for rolling upgrade. We have to disable the feature first, upgrade, and
then enable the feature. Otherwise, the old software cannot handle the new
heartbeat.
> Tha last datanode in a pipeline should send a heartbeat when there is no
> traffic
> --------------------------------------------------------------------------------
>
> Key: HDFS-7264
> URL: https://issues.apache.org/jira/browse/HDFS-7264
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Tsz Wo Nicholas Sze
> Attachments: h7264_20141017.patch
>
>
> When the client is writing slowly, the client will send a heartbeat to signal
> that the connection is still alive. This case works fine.
> However, when a client is writing fast but some of the datanodes in the
> pipeline are busy, a PacketResponder may get a timeout since no ack is sent
> from the upstream datanode. We suggest that the last datanode in a pipeline
> should send a heartbeat when there is no traffic.
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