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https://issues.apache.org/jira/browse/HADOOP-7933?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13178986#comment-13178986
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Siddharth Seth commented on HADOOP-7933:
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bq. Minor: Maybe store mountPoints.get.target.targetFileSystem in a temp
instead of invoking twice?
Could be done - but i don't believe this lookup is very expensive.
bq. It appears Credentials was selected for convenience since that's what the
MR's TokenCache uses internally? It appears Credentials was selected for
convenience since that's what the MR's TokenCache uses internally?
The API is limited private (at least for now) to MR and HDFS - so I don't see
this as a very big issue. Changing it to a set is a simple change though.
Thoughts ?
bq. Would it be reasonable to populate the Credentials/Set directly? Ie.
ViewFileSystem takes a set of existing tokens, then returns the subset of
tokens for its mounts that are not already in the existing tokens.
Was returning all tokens (instead of just new ones) to be consistent with the
existing API. Having this call populate tokens into the Credentials object was
an option - but that increases the cross-component dependency.
bq. I'm concerned that this appears to be creating a cross-component dependency
whereby ViewFileSystem it required to "assume" how MR's TokenCache will want
the tokens keyed within its Credentials.
I'm not very happy with this either - suggestion on a better approach ? Again,
being LimitedPrivate to MR and HDFS limits the impact.
bq. I also noticed getDelegationTokens(renewer,creds) is returning null where
getDelegationTokens(renewer) would return a 0-length list.
I believe getDelegationTokens(renewer, creds) is also returning an empty list
and not null.
However, there is a potential issue with the ViewFileSystem implementation -
{{result = new ArrayList<Token<?>>(initialListSize)}} - if there's multiple
mount points - part of the array will not be populated.
> Viewfs changes for MAPREDUCE-3529
> ---------------------------------
>
> Key: HADOOP-7933
> URL: https://issues.apache.org/jira/browse/HADOOP-7933
> Project: Hadoop Common
> Issue Type: Bug
> Affects Versions: 0.23.0
> Reporter: Siddharth Seth
> Assignee: Siddharth Seth
> Priority: Critical
> Fix For: 0.23.1
>
> Attachments: HADOOP-7933.txt, HADOOP7933_v1.txt, HADOOP7933_v2.txt,
> HDFS2665_v1.txt, HDFS2665_v1.txt
>
>
> ViewFs.getDelegationTokens returns a list of tokens for the associated
> namenodes. Credentials serializes these tokens using the service name for the
> actual namenodes. Effectively, tokens are not cached for viewfs (some more
> details in MR 3529). Affects any job which uses the TokenCache in tasks along
> with viewfs (some Pig jobs).
> Talk to Jitendra about this, some options
> 1. Change Credentials.getAllTokens to return the key, instead of just a token
> list (associate the viewfs canonical name with a token in credentials)
> 2. Have viewfs issue a fake token.
> Both of these would allow for a single viewfs configuration only.
> 3. An additional API in FileSystem - something like
> getDelegationTokens(String renewer, Credentials credentials) - which would
> check the credentials object before making token requests to the actual
> namenode.
> 4. An additional API in FileSystem - getCanonicalServiceNames - similar to
> getDelegationTokens, which would return service names for the actual
> namenodes. TokenCache/Credentials can work using this list.
> 5. have getDelegationTokens check the current UGI - and fetch tokens only if
> they don't exist.
> Have a quick patch for 3, along with associated MR changes.
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