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Posted to mapreduce-dev@hadoop.apache.org by "Robert Joseph Evans (JIRA)" <ji...@apache.org> on 2011/07/25 15:59:10 UTC
[jira] [Reopened] (MAPREDUCE-2572) Throttle the deletion of data
from the distributed cache
[ https://issues.apache.org/jira/browse/MAPREDUCE-2572?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Robert Joseph Evans reopened MAPREDUCE-2572:
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OK Aaron you convinced me. I'll submit a patch to bump it up to keep something like 95% of the maximum around in between garbage collections.
> 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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