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Posted to mapreduce-issues@hadoop.apache.org by "Todd Lipcon (JIRA)" <ji...@apache.org> on 2011/06/07 23:58:00 UTC

[jira] [Commented] (MAPREDUCE-2494) Make the distributed cache delete entires using LRU priority

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13045651#comment-13045651 ] 

Todd Lipcon commented on MAPREDUCE-2494:
----------------------------------------

Not sure why it didn't show up on the test-patch, but please take a look at MAPREDUCE-2573 - I think this commit added a findbugs warning.

> 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
>             Fix For: 0.23.0
>
>         Attachments: MAPREDUCE-2494-V1.patch, MAPREDUCE-2494-V2.patch
>
>
> 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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