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Date: Mon, 26 Apr 2010 14:02:35 -0400 (EDT)
From: "Konstantin Shvachko (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-1093) Improve namenode scalability by
 splitting the FSNamesystem synchronized section in a read/write lock
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    [ https://issues.apache.org/jira/browse/HDFS-1093?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12861015#action_12861015 ] 

Konstantin Shvachko commented on HDFS-1093:
-------------------------------------------

createfiles 3%, deletefiles 1%. Oh, that's why the clusters grow :-).
Does 1% for deletes counts directories and files? If people delete large directories then may be there is more than 1% of file deletes.

> 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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