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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5203) Concurrent clients that add a cache directive on the same path may prematurely uncache from each other.
Date Wed, 16 Oct 2013 23:11:43 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5203?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13797405#comment-13797405
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Colin Patrick McCabe commented on HDFS-5203:
--------------------------------------------

I guess it makes sense to be able to add multiple cache directives for the same path.  They
just get different IDs.  As you mentioned, that will make it easier for other programs to
use our API

> Concurrent clients that add a cache directive on the same path may prematurely uncache
from each other.
> -------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-5203
>                 URL: https://issues.apache.org/jira/browse/HDFS-5203
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: HDFS-4949
>            Reporter: Chris Nauroth
>            Assignee: Chris Nauroth
>
> When a client adds a cache directive, we assign it a unique ID and return that ID to
the client.  If multiple clients add a cache directive for the same path, then we return the
same ID.  If one client then removes the cache entry for that ID, then it is removed for all
clients.  Then, when this change becomes visible in subsequent cache reports, the datanodes
may {{munlock}} the block before the other clients are done with it.



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