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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6581) Write to single replica in memory
Date Thu, 21 Aug 2014 22:14:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6581?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14106042#comment-14106042
] 

Todd Lipcon commented on HDFS-6581:
-----------------------------------

If you truncate() a file while a reader has it mmapped, will the reader get 0s or a bus error?
I seem to recall it's the latter, which may be a bit nasty for a revocation path.

Why not do what we discussed a couple months back and have a disk replica with mlock? I think
this will prevent any writeback.

> Write to single replica in memory
> ---------------------------------
>
>                 Key: HDFS-6581
>                 URL: https://issues.apache.org/jira/browse/HDFS-6581
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>            Reporter: Arpit Agarwal
>            Assignee: Arpit Agarwal
>         Attachments: HDFSWriteableReplicasInMemory.pdf
>
>
> Per discussion with the community on HDFS-5851, we will implement writing to a single
replica in DN memory via DataTransferProtocol.
> This avoids some of the issues with short-circuit writes, which we can revisit at a later
time.



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