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From Rakesh R <rake...@huawei.com>
Subject RE: zookeeper in hadoop
Date Mon, 18 Aug 2014 16:04:22 GMT
>>>>>> what my doubt is from documentation if namenode maintains an persistent
session and the created node will not be deleted and how will it trigger standby namenode"

HDFS community is the right place to query this doubt. 
As I know NN uses ephemeral znodes to handle machine crashes and triggers watch event for
switching standby to active.

Regards,
Rakesh

-----Original Message-----
From: mufc_fan [mailto:rajeshkumarit8292@gmail.com] 
Sent: 18 August 2014 14:39
To: zookeeper-user@hadoop.apache.org
Subject: RE: zookeeper in hadoop

thank u for ur response...I have one doubt..In name node high availability, from documentation,
it  states that "each of the NameNode machines in the cluster maintains a persistent session
in ZooKeeper. If the machine crashes, the ZooKeeper session will expire, notifying the other
NameNode that a failover should be triggered"

According to my knowledge "if namenode creates an ephemeral node in zookeeper, when the machine
crashes the node gets delete which triggers the watch event so that standby name node creates
new ephemeral seesion with zookeeper and becomes new namenode". 

what my doubt is from documentation if namenode maintains an persistent session and the created
node will not be deleted and how will it trigger standby namenode"



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