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https://issues.apache.org/jira/browse/HADOOP-9748?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13712934#comment-13712934
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Kihwal Lee commented on HADOOP-9748:
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ensureInitialized() forced many frequently called methods to unconditionally
acquire the class lock. This patch certainly reduces the lock contention, but
the highly contended getCurrentUser() can still block many threads. I
understand this is being addressed in HADOOP-9749.
There may be something else we can do to improve this for namenode.
According to the "worst" jstack of a busy namenode I took, there were 29
BLOCKED handler threads. All of them were blocked on the UGI class lock. Here
is the breakdown:
- 2 ensureInitialized() - from non static synchronized methods. This Jira
will unblock these.
- 27 getCurrentUser()
Among the 27 threads that were blocked at getCurrentUser(),
- 18 FSPermissionChecker() - from FSNamesystem#getPermissionChecker() in most
namenode RPC methods
- 8 BlockTokenSecretManager#generateToken() - getBlockLocations()
- 1 NameNodeRpcServer.mkdirs
I think FSPermissionChecker can be modified to be created with a passed in UGI.
FSNamesystem can the one already stored in RPC server by calling
getRemoteUser(). This will eliminate a bulk of getCurrentUser() calls from
namenode RPC handlers. A similar change can be made to mkdirs. Block token
generation is not as straightforward. Even without it we can eliminate majority
of the calls. We could potentially do the same for other RPC servers.
I will file a HDFS jira for this. HADOOP-9749 is still needed since
getCurrentUser() is used everywhere beyond namenode RPC server.
+1 for this patch.
> Reduce blocking on UGI.ensureInitialized
> ----------------------------------------
>
> Key: HADOOP-9748
> URL: https://issues.apache.org/jira/browse/HADOOP-9748
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: security
> Affects Versions: 0.23.0, 2.0.0-alpha, 3.0.0
> Reporter: Daryn Sharp
> Assignee: Daryn Sharp
> Priority: Critical
> Attachments: HADOOP-9748.patch, HADOOP-9748.patch
>
>
> EnsureInitialized is always sync'ed on the class, when it should only sync if
> it actually has to initialize.
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