[HDFS-8246] Get HDFS file name based on block pool id and block id

• Type: New Feature
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Component/s: hdfs-client, namenode
• Labels: BB2015-05-TBR
• Assignee: feng xu
• Reporter: feng xu
• Created: 24/Apr/15 21:28
• Updated: 24/Nov/15 19:39
• Resolved: 24/Nov/15 19:38

Description

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
hdfs dfs [generic options] -fn <poolId> <blockId>

This feature is useful if you have HDFS block file name in local file system and want to find out the related HDFS file name in HDFS name space (http://stackoverflow.com/questions/10881449/how-to-find-file-from-blockname-in-hdfs-hadoop). Each HDFS block file name in local file system contains both block pool id and block id, for sample HDFS block file name /hdfs/1/hadoop/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 uniquely 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 combination of block pool id and a block id is uniquely related a HDFS file name.

The shell command and C/Java API do not map the block pool id to name node, so it’s user’s responsibility to talk to the correct name node in federation environment that has multiple name nodes. The block pool 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 file name reaches the new method String getFileName(String poolId, long blockId) in FSNamesystem in name node through RPC, and the new method does the followings,
(1) Validate the block pool id.
(2) Create Block based on the block id.
(3) Get BlockInfoContiguous from Block.
(4) Get BlockCollection from BlockInfoContiguous.
(5) Get file name from BlockCollection.

Issue Links

• is related to: HDFS-9064 NN old UI (block_info_xml) not available in 2.7.x
• is related to: HDFS-6663 Admin command to track file and locations from block id