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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4213) When the client calls hsync(), allows the client to update the file length in the NameNode
Date Thu, 22 Nov 2012 00:14:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13502468#comment-13502468
] 

Todd Lipcon commented on HDFS-4213:
-----------------------------------

This patch seems to only add the flag to hsync()'s parameters. It seems like a valid use case
to allow an hflush() which updates the NN's metadata without actually causing an fsync on
the datanodes.

Another suggested improvement for the API: can we take an EnumSet of flags, instead of a boolean?
Then if we have other flags we want to add for hsync/hflush, it will be easier to extend the
API for them in the future without adding a combinatorial number of functions. (eg I could
see a flag like FSYNC_AT_LEAST_ONE_DN being useful)
                
> When the client calls hsync(), allows the client to update the file length in the NameNode
> ------------------------------------------------------------------------------------------
>
>                 Key: HDFS-4213
>                 URL: https://issues.apache.org/jira/browse/HDFS-4213
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>    Affects Versions: 3.0.0
>            Reporter: Jing Zhao
>            Assignee: Jing Zhao
>         Attachments: HDFS-4213.001.patch, HDFS-4213.002.patch, HDFS-4213.003.patch
>
>
> As per discussion in HDFS-3960 and HDFS-2802, when clients that need strong consistency
update the file length at the NameNode, a special sync is required for getting the length
of the being written files when snapshots are taken for these files. This jira implements
this sync-with-updating-length by 1) calling ClientProtocol#fsync(), and 2) adding a new field
to ClientProtocol#fsync() to indicate the length information.

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