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From "John Zhuge (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-10289) Balancer configures DNs directly
Date Thu, 14 Apr 2016 08:01:25 GMT
John Zhuge created HDFS-10289:
---------------------------------

             Summary: Balancer configures DNs directly
                 Key: HDFS-10289
                 URL: https://issues.apache.org/jira/browse/HDFS-10289
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: balancer & mover
    Affects Versions: 2.6.0
            Reporter: John Zhuge
            Assignee: John Zhuge
            Priority: Critical


Balancer directly configures the 2 balance-related properties (bandwidthPerSec and concurrentMoves)
on the DNs involved.

Details:
* Before each balancing iteration, set the properties on all DNs involved in the current iteration.
* The DN property changes will not survive restart.
* Balancer gets the property values from command line or its config file.
* Need new DN APIs to query and set the 2 properties.
* No need to edit the config file on each DN or run {{hdfs dfsadmin -setBalancerBandwidth}}
to configure every DN in the cluster.

Pros:
* Improve ease of use because all configurations are done at one place, the balancer. We saw
many customers often forgot to set concurrentMoves properly since it is required on both DN
and Balancer.
* Support new DNs added between iterations
* Handle DN restarts between iterations
* May be able to dynamically adjust the thresholds in different iterations. Don't know how
useful though.

Cons:
* New DN property API
* A malicious/misconfigured balancer may overwhelm DNs. {{hdfs dfsadmin -setBalancerBandwidth}}
has the same issue. Also Balancer can only be run by admin.

Questions:
* Can we create {{BalancerConcurrentMovesCommand}} similar to {{BalancerBandwidthCommand}}?
Can Balancer use them directly without going through NN?

One proposal to implement HDFS-7466 calls for an API to query DN properties. DN Conf Servlet
returns all config properties. It does not return individual property and it does not return
the value set by {{hdfs dfsadmin -setBalancerBandwidth}}.



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