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From "Zesheng Wu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6507) Improve DFSAdmin to support HA cluster better
Date Thu, 12 Jun 2014 06:33:02 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6507?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14028870#comment-14028870
] 

Zesheng Wu commented on HDFS-6507:
----------------------------------

Fix one mistake:
bq. The existing refresh commands do not accept a host:port parameter. 
As [~jingzhao] mentioned, the generic option {{-fs}} can specify host:port for those commands.

To summarize, the main purpose of this jira is listed below:
# Make the default action correctly and naturally: a. Commands which should take effect on
ANN, will take effect on ANN by default; b.   Commands which should take effect on both ANN
and SNN, will take effect on both ANN and SNN by default
# Improve usability: a. Users do not need to care that which NN is active and what the NN's
host:port is, just run the command; b. Commands that should take effect on both ANN and SNN
needn't run twice with respective host:port.

> 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:
> 1. ClientProtocol
> 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, RefreshCallQueueProtocol
> 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
NNs.
> 3. ClientDatanodeProtocol
> Commands in this category are handled correctly, no need to improve.



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