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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6871) Improve NameNode performance when creating file
Date Tue, 19 Aug 2014 18:03:18 GMT

    [ 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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