[
https://issues.apache.org/jira/browse/HADOOP-9937?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13762056#comment-13762056
]
Colin Patrick McCabe commented on HADOOP-9937:
----------------------------------------------
We put a lock around getgrname_r by default, since a large percentage of
systems out there have an implementation that actually is not re-entrant
(despite the _r). So you may not get as large a speedup as you think by
removing the lock in {{UserGroupInformation#getGroupNames}} (unless you also
set {{hadoop.workaround.non.threadsafe.getpwuid}} to {{false}}).
You could create a custom lock just for group information (rather than
synchronizing on the big UGI lock), but I'm not sure how much that would help.
Do you have a more detailed proposal for how to change the synchronization here?
> Improvement of the group information refer frequency
> ----------------------------------------------------
>
> Key: HADOOP-9937
> URL: https://issues.apache.org/jira/browse/HADOOP-9937
> Project: Hadoop Common
> Issue Type: Improvement
> Components: security
> Affects Versions: 3.0.0
> Reporter: Shinichi Yamashita
> Priority: Minor
> Attachments: namenode-threaddump.txt
>
>
> The node (e.g. NameNode, ResourceManager) uses UGI.getGroupNames() now to get
> the information of the user's group who accessed it.
> In UGI.getGroupsNames(), synchronized is declared, but UGI instance by
> various methods each time and the node get different lock in getGroupName().
> For example, when cache time limit in userToGroupsMap of Groups expired and
> the node accepts many requests at the same time, each refers for group
> information in id command or JNI.
> To improve the refer frequency of the group information, it should change
> about synchronization.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
