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Date: Tue, 19 Aug 2014 18:03:18 +0000 (UTC)
From: "Colin Patrick McCabe (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12734982.1408436332566.34551.1408471398607@arcas>
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Subject: [jira] [Commented] (HDFS-6871) Improve NameNode performance when
 creating file
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    [ https://issues.apache.org/jira/browse/HDFS-6871?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14102559#comment-14102559 ] 

Colin Patrick McCabe commented on HDFS-6871:
--------------------------------------------

Good idea.

Can you add a comment near the {{if (!skipLogSync)}} code, explaining that we only should skip the log sync when this delete operation is part of a larger create-with-overwrite (or other) operation that does its own {{logSync}}?

+1 once that's addressed.

> Improve NameNode performance when creating file  
> -------------------------------------------------
>
>                 Key: HDFS-6871
>                 URL: https://issues.apache.org/jira/browse/HDFS-6871
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode, performance
>            Reporter: Yi Liu
>            Assignee: Yi Liu
>            Priority: Critical
>             Fix For: 2.6.0
>
>         Attachments: HDFS-6871.001.patch
>
>
> Creating file with overwrite flag will cause NN fall into flush edit logs and block other requests if the file exists.
> When we create a file with overwrite flag (default is true) in HDFS, NN will remove original file if it exists. In FSNamesystem#startFileInternal, NN already holds the write lock, it calls {{deleteInt}} if the file exists, there is logSync in {{deleteInt}}. So in this case, logSync is under write lock, it will heavily affect the NN performance. 
> We should ignore the force logSync in {{deleteInt}} in this case.


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