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https://issues.apache.org/jira/browse/HDFS-5203?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13768513#comment-13768513
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Colin Patrick McCabe commented on HDFS-5203:
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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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