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https://issues.apache.org/jira/browse/HADOOP-10077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13810427#comment-13810427
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Colin Patrick McCabe commented on HADOOP-10077:
-----------------------------------------------
The {{TestMetricsSystemImpl}} test failure is
https://issues.apache.org/jira/browse/HADOOP-9990, not related to this change.
> o.a.h.s.Groups should refresh in the background
> -----------------------------------------------
>
> Key: HADOOP-10077
> URL: https://issues.apache.org/jira/browse/HADOOP-10077
> Project: Hadoop Common
> Issue Type: Bug
> Affects Versions: 2.2.1
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
> Attachments: HADOOP-10077.001.patch
>
>
> {{org.apache.hadoop.security.Groups}} maintains a cache of mappings between
> user names and sets of associated group names. Periodically, the entries in
> this cache expire and must be refetched from the operating system.
> Currently, this is done in the context of whatever thread happens to try to
> access the group mapping information right after the time period expires.
> However, this is problematic, since that thread may be holding the
> {{FSNamesystem}} lock. This means that if the
> {{GroupMappingServiceProvider}} is slow, the whole NameNode may grind to a
> halt until it finishes. This can generate periodic load spikes or even
> NameNode failovers.
> Instead, we should allow the refreshing of the group mappings to be done
> asynchronously in a background thread pool.
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