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From Rakesh R <rake...@huawei.com>
Subject RE: zookeeper in hadoop
Date Mon, 18 Aug 2014 08:24:21 GMT

AFAIK following are few cases where ZK is used in Hadoop & BookKeeper components.

Hadoop is using ZK to provides the high-availability of the Master process like,

1) HDFS is using ZK for making the NameNode highly available. 
Also, BKJM(uses BookKeeper as journal manager) which is a sub-module in the HDFS to store
WAL(editlog transactions)

2) YARN is using ZK for making the ResourceManager highly available. 
Also, they are using it for storing the state of the RM in ZooKeeper(ZKRMStateStore: A ZooKeeper-based
state-store implementation)

BookKeeper is using ZK for :

1) service discovery - to know the details about the running BK servers
2) metadata storage - keeps all the meta data about the ledgers(user data)
3) Auto-recovery - handle missing replicas to improve the fault-tolerance.

-----Original Message-----
From: mufc_fan [mailto:rajeshkumarit8292@gmail.com] 
Sent: 18 August 2014 11:25
To: zookeeper-user@hadoop.apache.org
Subject: zookeeper in hadoop

I am new to zookeeper and from the documentation I learnt that "zookeeper is a sub-project
of hadoop". so zookeeper must be used in hadoop. Can any one share their knowledge how zookeeper
is used in hadoop with simple example.

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