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From "Robert Joseph Evans (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-2572) Throttle the deletion of data from the distributed cache
Date Tue, 07 Jun 2011 16:51:58 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2572?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13045533#comment-13045533
] 

Robert Joseph Evans commented on MAPREDUCE-2572:
------------------------------------------------

The patch I posted is against 20.S I am working on a patch for trunk too.

> Throttle the deletion of data from the distributed cache
> --------------------------------------------------------
>
>                 Key: MAPREDUCE-2572
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2572
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: distributed-cache
>    Affects Versions: 0.20.205.0
>            Reporter: Robert Joseph Evans
>            Assignee: Robert Joseph Evans
>         Attachments: THROTTLING-security-v1.patch
>
>
> When deleting entries from the distributed cache we do so in a background thread.  Once
the size limit of the distributed cache is reached all unused entries are deleted.  MAPREDUCE-2494
changes this so that entries are deleted in LRU order until the usage falls below a given
threshold.  In either of these cases we are periodically flooding a disk with delete requests
which can slow down all IO operations to a drive.  It would be better to be able to throttle
this deletion so that it is spread out over a longer period of time.  This jira is to add
in this throttling.
> On investigating it seems much simpler to backport MPAREDUCE-2494 to 20S before implementing
this change rather then try to implement it without LRU deletion, because LRU goes a long
way towards reducing the load on the disk anyways.

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