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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-10077) o.a.h.s.Groups should refresh in the background
Date Thu, 31 Oct 2013 16:59:21 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-10077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13810427#comment-13810427

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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