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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4702) remove namesystem lock from DatanodeManager#fetchDatanodes
Date Tue, 16 Apr 2013 03:08:15 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13632525#comment-13632525

Chris Nauroth commented on HDFS-4702:

The lock happens in {{DatanodeManager#fetchDatanodes}}, but it's not immediately obvious to
me why we need the namesystem lock here.  Perhaps it's related to the edit log ops {{OP_DATANODE_ADD}}
and {{OP_DATANODE_REMOVE}}, which are deprecated and now appear to be unused?  Maybe it's
safe to remove the lock now, but this will need more investigation.
> remove namesystem lock from DatanodeManager#fetchDatanodes
> ----------------------------------------------------------
>                 Key: HDFS-4702
>                 URL: https://issues.apache.org/jira/browse/HDFS-4702
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 3.0.0
>            Reporter: Chris Nauroth
> {{DatanodeManager#fetchDatanodes}} currently holds the namesystem read lock while iterating
through data nodes.  This method is called from the namenode web UI.  HDFS-3990 reported a
performance problem in this code path.  This is a follow-up jira to investigate whether or
not we can remove the lock.

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