HDFS - Heartbeat (Dead datanode)

About

Each DataNode sends a Heartbeat message to the NameNode periodically.

The NameNode marks DataNodes without recent Heartbeats as dead and does not forward any new IO requests to them.

Configuration

The time-out to mark DataNodes dead is conservatively long (over 10 minutes by default) in order to avoid replication storm caused by state flapping of DataNodes.

Interval

<property>
  <name>dfs.heartbeat.interval</name>
  <value>3</value>
</property>
hdfs getconf -confKey dfs.heartbeat.interval

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