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https://issues.apache.org/jira/browse/HDFS-3979?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13467292#comment-13467292
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Luke Lu commented on HDFS-3979:
-------------------------------

bq. Do we want the change?

I do think that the change is required for the correct hsync semantics (and 
better hflush guarantee). I'm not too sure if the change is complete without 
some reasonable test cases for failure scenarios.

BTW, do you have any new performance numbers for comparison as well?
                
> Fix hsync and hflush semantics.
> -------------------------------
>
>                 Key: HDFS-3979
>                 URL: https://issues.apache.org/jira/browse/HDFS-3979
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node, hdfs client
>    Affects Versions: 0.22.0, 0.23.0, 2.0.0-alpha
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>         Attachments: hdfs-3979-sketch.txt, hdfs-3979-v2.txt
>
>
> See discussion in HDFS-744. The actual sync/flush operation in BlockReceiver 
> is not on a synchronous path from the DFSClient, hence it is possible that a 
> DN loses data that it has already acknowledged as persisted to a client.
> Edit: Spelling.

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