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https://issues.apache.org/jira/browse/HDFS-12357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16151587#comment-16151587
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Chris Douglas commented on HDFS-12357:
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bq. if we can avoid duplicate of components, it would be great.
Are there any clusters that benefit from this optimization? The fraction of
calls for distcp jobs, in clusters with an external attribute provider
configured, run by a particular user is unlikely to be significant. This cost
is currently incurred by _every_ call with an external attribute provider.
Again, if this cost is significant, then it should be optimized across external
attribute providers (moving this logic into {{INodeAttributeProvider}}).
The approach in v001\* is difficult to extend. For example, if another
developer were to add a config knob that bypassed particular paths, then it
would have to work around the logic in {{FSDirectory}}.
> 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-12357.001a.patch, HDFS-12357.001b.patch,
> HDFS-12357.001.patch, HDFS-12357.002.patch, HDFS-12357.003.patch,
> HDFS-12357.004.patch, HDFS-12357.005.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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