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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 Fri, 11 Oct 2013 17:40:43 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13792855#comment-13792855
] 

Chris Nauroth commented on HDFS-5096:
-------------------------------------

In {{CacheManager#setCachedLocations}}, we need a check for {{enabled}}.  Otherwise, with
caching disabled, we have a null {{cachedBlocks}}, and the method ends up throwing {{NullPointerException}}.

I see you have already added a check in that method for getting a null block (uncached block)
out of the map.  That's good too.

> 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
>
>
> 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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