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From: "Tsz Wo Nicholas Sze (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-8246) Get HDFS file name based on block
 pool id and block id
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    [ https://issues.apache.org/jira/browse/HDFS-8246?page=3Dcom.atlassian.=
jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D14586=
649#comment-14586649 ]=20

Tsz Wo Nicholas Sze commented on HDFS-8246:
-------------------------------------------

What are the more use cases?

> Get HDFS file name based on block pool id and block id
> ------------------------------------------------------
>
>                 Key: HDFS-8246
>                 URL: https://issues.apache.org/jira/browse/HDFS-8246
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: HDFS, hdfs-client, namenode
>            Reporter: feng xu
>            Assignee: feng xu
>              Labels: BB2015-05-TBR
>         Attachments: HDFS-8246.0.patch
>
>
> This feature provides HDFS shell command and C/Java API to retrieve HDFS =
file name based on block pool id and block id.
> 1. The Java API in class DistributedFileSystem
> public String getFileName(String poolId, long blockId) throws IOException
> 2. The C API in hdfs.c
> char* hdfsGetFileName(hdfsFS fs, const char* poolId, int64_t blockId)
> 3. The HDFS shell command=20
>  hdfs dfs [generic options] -fn <poolId> <blockId>
> This feature is useful if you have HDFS block file name in local file sys=
tem and want to  find out the related HDFS file name in HDFS name space (ht=
tp://stackoverflow.com/questions/10881449/how-to-find-file-from-blockname-i=
n-hdfs-hadoop).  Each HDFS block file name in local file system contains bo=
th block pool id and block id, for sample HDFS block file name /hdfs/1/hado=
op/hdfs/data/current/BP-97622798-10.3.11.84-1428081035160/current/finalized=
/subdir0/subdir0/blk_1073741825,  the block pool id is BP-97622798-10.3.11.=
84-1428081035160 and the block id is 1073741825. The block  pool id is uniq=
uely related to a HDFS name node/name space,  and the block id is uniquely =
related to a HDFS file within a HDFS name node/name space, so the combinati=
on of block pool id and a block id is uniquely related a HDFS file name.=20
> The shell command and C/Java API do not map the block pool id to name nod=
e, so it=E2=80=99s user=E2=80=99s responsibility to talk to the correct nam=
e node in federation environment that has multiple name nodes. The block po=
ol id is used by name node to check if the user is talking with the correct=
 name node.
> The implementation is straightforward. The client request to get HDFS fil=
e name reaches the new method String getFileName(String poolId, long blockI=
d) in FSNamesystem in name node through RPC,  and the new method does the f=
ollowings,
> (1)=09Validate the block pool id.
> (2)=09Create Block  based on the block id.
> (3)=09Get BlockInfoContiguous from Block.
> (4)=09Get BlockCollection from BlockInfoContiguous.
> (5)=09Get file name from BlockCollection.



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