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From "Gopal V (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5957) Provide support for different mmap cache retention policies in ShortCircuitCache.
Date Mon, 03 Mar 2014 20:59:22 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13918566#comment-13918566
] 

Gopal V commented on HDFS-5957:
-------------------------------

[~cnauroth]: I will cycle back to this once I've get more hive specific stuff worked out.
I think setting the size to 1 will probably work itself out for me, setting it to zero doesn't
seem to work at all (i.e only cache it within the open InputStream, not within a cross-thread
cache).

> 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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