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Posted to common-user@hadoop.apache.org by mufc_fan <ra...@gmail.com> on 2014/10/30 10:02:03 UTC
Hadoop namenode high availability
Hai...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 deleted 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"
can any one share your knowledge
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Re: Hadoop namenode high availability
Posted by Ivan Kelly <iv...@apache.org>.
I'm not sure what they are trying to say with "persistent" session. A
session in zookeeper has a timeout associated with it. If the server
doesn't hear from the client within the timeout period the session is
expired, and all ephemeral nodes associated with the session are
deleted. This is what triggers the failover. The text you posted seems
to be confusing the concepts of session and ephemeral node.
-Ivan
On 30 October 2014 10:02, mufc_fan <ra...@gmail.com> wrote:
> Hai...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 deleted 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"
>
> can any one share your knowledge
>
>
>
> --
> View this message in context: http://hadoop-common.472056.n3.nabble.com/Hadoop-namenode-high-availability-tp4054804.html
> Sent from the Users mailing list archive at Nabble.com.