Fengnan Li created HDFS-15383:
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             Summary: RBF: Disable watch in ZKDelegationSecretManager for 
performance
                 Key: HDFS-15383
                 URL: https://issues.apache.org/jira/browse/HDFS-15383
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: Fengnan Li
            Assignee: Fengnan Li


Based on the current design for delegation token in secure Router, the total 
number of watches for tokens is the product of number of routers and number of 
tokens, this is due to ZKDelegationTokenManager is using PathChildrenCache from 
curator, which automatically sets the watch and ZK will push the sync 
information to each router. There are some evaluations about the number of 
watches in Zookeeper has negative performance impact to Zookeeper server.

In our practice when the number of watches exceeds 1.2 Million in a single ZK 
server there will be significant ZK performance degradation. Thus this ticket 
is to rewrite ZKDelegationTokenManagerImpl.java to explicitly disable the 
PathChildrenCache and have Routers sync periodically from Zookeeper. This has 
been working fine at the scale of 10 Routers with 2 million tokens. 



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