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From "Manoj Govindassamy (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12357) Let NameNode to bypass external attribute provider for special user
Date Fri, 01 Sep 2017 17:51:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16150921#comment-16150921
] 

Manoj Govindassamy commented on HDFS-12357:
-------------------------------------------

Thanks for working on this [~yzhangal]. Thanks [~chris.douglas] for your review and comments.

I believe the motive here is to strictly not return any of external provider attributes for
certain users. Tools like distcp can listFileStatus() as this special user to get plain/standalone
hdfs attributes which can then be _safely_ copied to a remote hdfs. We might not want tools
like DistCp to copy external attributes to HDFS. 

Now, this knob/control for returning external attributes can either be given to HDFS or the
external provider. While having all the logics about returning the right set of attributes
at a single place, like the provider does sound like very good idea, there is still a gap
in the design. If I understand the problem rightly, here the choice need to be given to HDFS
whether to contact external attributes provider or return the local default provider, so as
to be totally sure that right set of attributes are returned. May be this guarantee is not
established if the control is placed at the external provider. 


> Let NameNode to bypass external attribute provider for special user
> -------------------------------------------------------------------
>
>                 Key: HDFS-12357
>                 URL: https://issues.apache.org/jira/browse/HDFS-12357
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Yongjun Zhang
>            Assignee: Yongjun Zhang
>         Attachments: HDFS-12357.001.patch
>
>
> This is a third proposal to solve the problem described in HDFS-12202.
> The problem is, when we do distcp from one cluster to another (or within the same cluster),
in addition to copying file data, we copy the metadata from source to target. If external
attribute provider is enabled, the metadata may be read from the provider, thus provider data
read from source may be saved to target HDFS. 
> We want to avoid saving metadata from external provider to HDFS, so we want to bypass
external provider when doing the distcp (or hadoop fs -cp) operation.
> Two alternative approaches were proposed earlier, one in HDFS-12202, the other in HDFS-12294.
The proposal here is the third one.
> The idea is, we introduce a new config, that specifies a special user (or a list of users),
and let NN bypass external provider when the current user is a special user.
> If we run applications as the special user that need data from external attribute provider,
then it won't work. So the constraint on this approach is, the special users here should not
run applications that need data from external provider.
> Thanks [~asuresh] for proposing this idea and [~chris.douglas], [~daryn], [~manojg] for
the discussions in the other jiras. 
> I'm creating this one to discuss further.



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