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https://issues.apache.org/jira/browse/HDFS-5957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13918591#comment-13918591
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Chris Nauroth commented on HDFS-5957:
-------------------------------------

Thanks, [~gopalv].

bq. setting it to zero doesn't seem to work at all

That's correct.  Zero is interpreted as a special value meaning "don't do any 
mmaps".

> Provide support for different mmap cache retention policies in 
> ShortCircuitCache.
> ---------------------------------------------------------------------------------
>
>                 Key: HDFS-5957
>                 URL: https://issues.apache.org/jira/browse/HDFS-5957
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>    Affects Versions: 2.3.0
>            Reporter: Chris Nauroth
>
> Currently, the {{ShortCircuitCache}} retains {{mmap}} regions for reuse by 
> multiple reads of the same block or by multiple threads.  The eventual 
> {{munmap}} executes on a background thread after an expiration period.  Some 
> client usage patterns would prefer strict bounds on this cache and 
> deterministic cleanup by calling {{munmap}}.  This issue proposes additional 
> support for different caching policies that better fit these usage patterns.



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