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From "Zesheng Wu (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-6507) Improve DFSAdmin to support HA cluster better
Date Tue, 10 Jun 2014 07:21:03 GMT
Zesheng Wu created HDFS-6507:

             Summary: Improve DFSAdmin to support HA cluster better
                 Key: HDFS-6507
                 URL: https://issues.apache.org/jira/browse/HDFS-6507
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: tools
    Affects Versions: 2.4.0
            Reporter: Zesheng Wu
            Assignee: Zesheng Wu

Currently, the commands supported in DFSAdmin can be classified into three categories according
to the protocol used:
Commands in this category generally implement by calling the corresponding function of the
DFSClient class, and will call the corresponding remote implementation function at the NN
side finally. At the NN side, all these operations are classified into five categories: UNCHECKED,
READ, WRITE, CHECKPOINT, JOURNAL. Active NN will allow all operations, and Standby NN only
allows UNCHECKED operations. In the current implementation of DFSClient, it will connect one
NN first, if the first NN is not Active and the operation is not allowed, it will failover
to the second NN. So here comes the problem, some of the commands(setSafeMode, saveNameSpace,
restoreFailedStorage, refreshNodes, setBalancerBandwidth, metaSave) in DFSAdmin are classified
as UNCHECKED operations, and when executing these commands in the DFSAdmin command line, they
will be sent to a definite NN, no matter it is Active or Standby. This may result in two problems:

a. If the first tried NN is standby, and the operation takes effect only on Standby NN, which
is not the expected result.
b. If the operation needs to take effect on both NN, but it takes effect on only one NN. In
the future, when there is a NN failover, there may have problems.
Here I propose the following improvements:
a. If the command can be classified as one of READ/WRITE/CHECKPOINT/JOURNAL operations, we
should classify it clearly.
b. If the command can not be classified as one of the above four operations, or if the command
needs to take effect on both NN, we should send the request to both Active and Standby NNs.

2.Refresh protocols: RefreshAuthorizationPolicyProtocol, RefreshUserMappingsProtocol, RefreshUserMappingsProtocol,
Commands in this category, including refreshServiceAcl, refreshUserToGroupMapping, refreshSuperUserGroupsConfiguration
and refreshCallQueue, are implemented by creating a corresponding RPC proxy and sending the
request to remote NN. In the current implementation, these requests will be sent to a definite
NN, no matter it is Active or Standby. Here I propose that we sent these requests to both

Commands in this category are handled correctly, no need to improve.

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