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Date: Tue, 5 Apr 2011 17:57:06 +0000 (UTC)
From: "Suresh Srinivas (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-1148) Convert FSDataset to ReadWriteLock
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    [ https://issues.apache.org/jira/browse/HDFS-1148?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13016050#comment-13016050 ] 

Suresh Srinivas commented on HDFS-1148:
---------------------------------------

Todd, I want to understand what methods have lot contention. Also you say:
> As I understood it, the non-fair mode is more efficient. Since the lock is mostly uncontended

I am not sure what you mean mostly uncontended, because I understand the problem description as there are lot of contentions...

> Convert FSDataset to ReadWriteLock
> ----------------------------------
>
>                 Key: HDFS-1148
>                 URL: https://issues.apache.org/jira/browse/HDFS-1148
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: data-node
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-1148-old.txt, patch-HDFS-1148-rel0.20.2.txt
>
>
> In benchmarking HDFS-941 I noticed that for the random read workload, the FSDataset lock is highly contended. After converting it to a ReentrantReadWriteLock, I saw a ~25% improvement on both latency and ops/second.

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