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What is Heartbeat in Hadoop? |
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Answer» Because the Namenode and Datanode in Hadoop are two physically SEPARATE machines, Heartbeat is the signal transmitted by the Datanode to the Namenode at regular intervals to confirm its existence, i.e. that it is alive. If Namenode does not receive a heartbeat from a Datanode within a specific timeframe (usually 10 minutes), Namenode CONSIDERS the Datanode to be DEAD. Along with the heartbeat, the Datanode also TRANSMITS the block report to Namenode, which normally contains a list of all the blocks on the Datanode. |
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