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From "Robert Joseph Evans (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-2494) Make the distributed cache delete entires using LRU priority
Date Fri, 13 May 2011 16:32:47 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13033113#comment-13033113
] 

Robert Joseph Evans commented on MAPREDUCE-2494:
------------------------------------------------

I agree completely.  The 10 min is already configurable, sort of.  It should also be very
simple to add it in.  The hardest part will probably be updating the tests.  I figure I will
make the reference count inc/dec in the CacheStatus methods, and then if the reference count
ever goes to 0 we update a timestamp to indicate when it was last used, so we can purge oldest
objects first.

> Make the distributed cache delete entires using LRU priority
> ------------------------------------------------------------
>
>                 Key: MAPREDUCE-2494
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2494
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: distributed-cache
>    Affects Versions: 0.21.0
>            Reporter: Robert Joseph Evans
>            Assignee: Robert Joseph Evans
>
> Currently the distributed cache will wait until a cache directory is above a preconfigured
threshold.  At which point it will delete all entries that are not currently being used. 
It seems like we would get far fewer cache misses if we kept some of them around, even when
they are not being used.  We should add in a configurable percentage for a goal of how much
of the cache should remain clear when not in use, and select objects to delete based off of
how recently they were used, and possibly also how large they are/how difficult is it to download
them again.

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