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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 Mon, 16 Sep 2013 17:24:54 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5203?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13768513#comment-13768513
] 

Colin Patrick McCabe commented on HDFS-5203:
--------------------------------------------

In HDFS-5213, I switched it to just refuse to add multiple cache directives for the same path
in the same pool.  It seems like that is more intuitive for system administrators.  However,
I can see how allowing multiple identical directives in the same pool might be more useful
for programs using the API directly.  I'm not sure which way we should go here.
                
> 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
>
> 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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