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https://issues.apache.org/jira/browse/HDFS-6764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14076339#comment-14076339
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Daryn Sharp commented on HDFS-6764:
-----------------------------------
This was prominently observed on a HA standby due to HDFS-6763. Quota recalcs
caused all DNs to heartbeat in the same second. For a yet unknown reason, HA
actives demonstrate a similar rhythmic clumping heartbeats but not to the same
degree.
> DN heartbeats may become clumped together
> -----------------------------------------
>
> Key: HDFS-6764
> URL: https://issues.apache.org/jira/browse/HDFS-6764
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Daryn Sharp
>
> DNs send heartbeats on a fixed schedule based on the last time a heartbeat
> was sent. If the NN takes longer to respond than the heartbeat interval then
> DNs do not sleep until the next interval. Instead, another heartbeat is
> immediately sent and all DNs begin heartbeating on the same schedule.
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