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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6581) Write to single replica in memory
Date Thu, 21 Aug 2014 22:28:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6581?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14106069#comment-14106069
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Colin Patrick McCabe commented on HDFS-6581:
--------------------------------------------

bq. 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.

A reader which reads via read() will get EOF.  A reader reading via mmap will get SIGBUS.
 It's not nasty, because we only do this after telling the client to stop reading using the
mechanism in HDFS-5182.  The client only ever has problems if it goes rogue and decides to
ignore our message telling it to stop reading.

> 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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