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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5096) Automatically cache new data added to a cached path
Date Wed, 16 Oct 2013 18:53:44 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13797122#comment-13797122

Colin Patrick McCabe commented on HDFS-5096:

bq. hdfs-default.xml: Let's document dfs.namenode.path.based.cache.refresh.interval.ms.


bq. IntrusiveCollection#addFirst: This method appears to be only called from test code. Do
you want to keep it, or is it better to delete it?

It's a pretty small function.  I'd like to keep it in case it's needed later.  Since we have
a doubly-linked list, being able to add at the beginning or the end is a nice feature.

bq. TestPathBasedCacheRequests#waitForCachedBlocks: This is another spot where I think we
should use GenericTestUtils#waitFor. Even though the JUnit-level timeouts would abort, this
tends to leave the process hanging around. GenericTestUtils#waitFor would throw and exit more

Good idea.

> 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,
HDFS-5096-caching.010.patch, HDFS-5096-caching.011.patch, HDFS-5096-caching.012.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
> 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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