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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5957) Provide support for different mmap cache retention policies in ShortCircuitCache.
Date Mon, 03 Mar 2014 23:49:25 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13918752#comment-13918752
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Chris Nauroth commented on HDFS-5957:
-------------------------------------

bq. Yeah. I wonder if we should revisit that and create a separate 'enable' flag for the client,
before the configuration here gets set in stone.

I suppose the advantage of a separate flag is that you can then legitimately set the size
to 0 if you know you want mmap but no caching.  It seems more flexible, so I'm +1 for that
proposal.

> 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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