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From "Robert Joseph Evans (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-2572) Throttle the deletion of data from the distributed cache
Date Tue, 07 Jun 2011 14:02:58 GMT
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


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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