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From "Ming Ma (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-7442) Optimization for decommission-in-progress check
Date Tue, 25 Nov 2014 07:16:12 GMT
Ming Ma created HDFS-7442:

             Summary: Optimization for decommission-in-progress check
                 Key: HDFS-7442
                 URL: https://issues.apache.org/jira/browse/HDFS-7442
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: Ming Ma

1. {{isReplicationInProgress }} currently rescan all blocks of a given node each time the
method is called; it becomes less efficient as more of its blocks become fully replicated.
Each scan takes FS lock.

2. As discussed in HDFS-7374, if the node becomes dead during decommission, it is useful if
the dead node can be marked as decommissioned after all its blocks are fully replicated. Currently
there is no way to check the blocks of dead decomm-in-progress nodes, given the dead node
is removed from blockmap.

There are mitigations for these limitations. Set dfs.namenode.decommission.nodes.per.interval
to small value for reduce the duration of lock. HDFS-7409 uses global FS state to tell if
a dead node's blocks are fully replicated.

To address these scenarios, it will be useful to track the decommon-in-progress blocks separately.

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