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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5096) Automatically cache new data added to a cached path
Date Tue, 15 Oct 2013 21:42:02 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13795681#comment-13795681
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Chris Nauroth commented on HDFS-5096:
-------------------------------------

Regarding those comments, it looks to me like the logic is correct, but the comments have
inverted the phrases "too few" and "too many".  The first path is for {{neededCached <=
numCached}}, but its comment says "too few" cached replicas.  The second path is for {{neededCached
>= numCached}}, but its comment says "too many" cached replicas.

Thanks for addressing the feedback, Colin.  At this point, I've looked at all of the main
code, so I expect this is the last of my feedback on that.  I haven't looked at test code
yet.  I'll take a look at that when the next patch version gets posted.

> Automatically cache new data added to a cached path
> ---------------------------------------------------
>
>                 Key: HDFS-5096
>                 URL: https://issues.apache.org/jira/browse/HDFS-5096
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: datanode, namenode
>            Reporter: Andrew Wang
>            Assignee: Colin Patrick McCabe
>         Attachments: HDFS-5096-caching.005.patch, HDFS-5096-caching.006.patch, HDFS-5096-caching.009.patch
>
>
> For some applications, it's convenient to specify a path to cache, and have HDFS automatically
cache new data added to the path without sending a new caching request or a manual refresh
command.
> One example is new data appended to a cached file. It would be nice to re-cache a block
at the new appended length, and cache new blocks added to the file.
> Another example is a cached Hive partition directory, where a user can drop new files
directly into the partition. It would be nice if these new files were cached.
> In both cases, this automatic caching would happen after the file is closed, i.e. block
replica is finalized.



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