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https://issues.apache.org/jira/browse/HDFS-15900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17303794#comment-17303794
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Harunobu Daikoku commented on HDFS-15900:
-----------------------------------------

Thanks [~aajisaka] for your detailed analysis and a further suggestion.

bq. we expect the federationSpaceInfo of both AVAILABLE and UNAVAILABLE 
NameNodes are set in activeNamespaces,

I want to make sure if it's ok to have several records sharing the same 
nameserviceId in activeNamespaces, a "set" of FederationNamespaceInfo which, as 
in the code comment,  is supposed to represent a nameservice, not a NameNode.
https://github.com/apache/hadoop/blob/rel/release-3.3.0/hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/FederationNamespaceInfo.java#L23-L24

> RBF: empty blockpool id on dfsrouter caused by UNAVAILABLE NameNode
> -------------------------------------------------------------------
>
>                 Key: HDFS-15900
>                 URL: https://issues.apache.org/jira/browse/HDFS-15900
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: rbf
>    Affects Versions: 3.3.0
>            Reporter: Harunobu Daikoku
>            Priority: Major
>         Attachments: image.png
>
>
> We observed that when a NameNode becomes UNAVAILABLE, the corresponding 
> blockpool id in MembershipStoreImpl#activeNamespaces on dfsrouter 
> unintentionally sets to empty, its initial value.
>  !image.png|height=250!
> As a result of this, concat operations through dfsrouter fail with the 
> following error as it cannot resolve the block id in the recognized active 
> namespaces.
> {noformat}
> Caused by: 
> org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.ipc.RemoteException): 
> Cannot locate a nameservice for block pool BP-...
> {noformat}
> A possible fix is to ignore UNAVAILABLE NameNode registrations, and set 
> proper namespace information obtained from available NameNode registrations 
> when constructing the cache of active namespaces.
>  
> [https://github.com/apache/hadoop/blob/rel/release-3.3.0/hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/impl/MembershipStoreImpl.java#L207-L221]



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