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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4222) NN is unresponsive and lose heartbeats of DNs when Hadoop is configured to use LDAP and LDAP has issues
Date Thu, 21 Feb 2013 16:08:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4222?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13583310#comment-13583310
] 

Kihwal Lee commented on HDFS-4222:
----------------------------------

bq. "lockGroups" would internally fetch the groups and then make them immutable in the UGI.


This will ensure group lookups happen before entering a critical section. But since mappings
are cached in Groups and the UGI is short-lived, simply calling getGroups() early will be
enough. One concern in early lookup is whether it will generate excessive extra lookups. Some
methods in client protocol don't need permission checks as they are lease-based. For example,
addBlock(), complete() and renewLease() are lease-based and their request rate is quite high.
In a busy grid, they add up to over 450 requests/sec. But again, caching may reduce actual
lookups, so it may not be a big deal.

If unconditionally forced early lookup is not acceptable, we could selectively do early lookup/cache-filling
in NameNodeRpcServer for those calls that actually need group lookups and leave FSNamesystem
mostly unchanged.
                
> NN is unresponsive and lose heartbeats of DNs when Hadoop is configured to use LDAP and
LDAP has issues
> -------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-4222
>                 URL: https://issues.apache.org/jira/browse/HDFS-4222
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 1.0.0, 0.23.3, 2.0.0-alpha
>            Reporter: Xiaobo Peng
>            Assignee: Xiaobo Peng
>            Priority: Minor
>         Attachments: hdfs-4222-branch-0.23.3.patch, HDFS-4222.patch, HDFS-4222.patch,
hdfs-4222-release-1.0.3.patch
>
>
> For Hadoop clusters configured to access directory information by LDAP, the FSNamesystem
calls on behave of DFS clients might hang due to LDAP issues (including LDAP access issues
caused by networking issues) while holding the single lock of FSNamesystem. That will result
in the NN unresponsive and loss of the heartbeats from DNs.
> The places LDAP got accessed by FSNamesystem calls are the instantiation of FSPermissionChecker,
which could be moved out of the lock scope since the instantiation does not need the FSNamesystem
lock. After the move, a DFS client hang will not affect other threads by hogging the single
lock. This is especially helpful when we use separate RPC servers for ClientProtocol and DatanodeProtocol
since the calls for DatanodeProtocol do not need to access LDAP. So even if DFS clients hang
due to LDAP issues, the NN will still be able to process the requests (including heartbeats)
from DNs.

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