[jira] [Created] (HDFS-8875) Optimize the wait time in Balancer for federation scenario

["Ming Ma (JIRA)" <ji...@apache.org>]

Ming Ma created HDFS-8875:
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             Summary: Optimize the wait time in Balancer for federation scenario
                 Key: HDFS-8875
                 URL: https://issues.apache.org/jira/browse/HDFS-8875
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: Ming Ma
            Assignee: Chris Trezzo


Balancer has wait time between two consecutive iterations. That is to give some time for block movement to be fully committed ( return from replaceBlock doesn't mean the NN's blockmap has been updated and the block has been invalidated on the source node.).

This wait time could be 23 seconds if {{dfs.heartbeat.interval}} is set to 10 and {{dfs.namenode.replication.interval}} is to 3. In the case of federation, given we iterate through all namespaces in each iteration, this wait time becomes unnecessary as while balancer is processing the next namespace, it gives the previous namespace it just finished time to commit.

In addition, Balancer calls {{Collections.shuffle(connectors);}} It doesn't seem necessary.



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