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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1093) Improve namenode scalability by splitting the FSNamesystem synchronized section in a read/write lock
Date Mon, 26 Apr 2010 07:17:38 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1093?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12860834#action_12860834
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dhruba borthakur commented on HDFS-1093:
----------------------------------------

A typical analysis of the workload in our cluster shows that the following types of RPC are
processed by the namenode:

listStatus   47%
openfiles    42%
createfiles  3%
mkdirs       3%
rename       2%
deletefiles  1%


> Improve namenode scalability by splitting the FSNamesystem synchronized section in a
read/write lock
> ----------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-1093
>                 URL: https://issues.apache.org/jira/browse/HDFS-1093
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: NNreadwriteLock.txt
>
>
> Most critical data structures in the NameNode (NN) are protected by a syncronized methods
in the FSNamesystem class. This essentially makes critical code paths in the NN single-threaded.
However, a large percentage of the NN calls are listStatus, getBlockLocations, etc which do
not change internal data structures at all, these are read-only calls. If we change the FSNamesystem
lock to a read/write lock, many of the above operations can occur in parallel, thus improving
the scalability of the NN.

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