Abhijit, I do not think that the blocks' locations are exposed by the DataNode yet. The reads by DFSClient are done in a remote fashion (yes, even for local reads), so only the DataNode knows the ID->File mapping and never the Clients.
I'm not sure what you're attempting to do, but perhaps https://issues.apache.org/jira/browse/HDFS-2246 and its relevant JIRAs would interest you. It did add in a mechanism to expose out the blocks' whole path, available to read in the patch. On 31-Oct-2011, at 6:51 AM, Abhijit Rao wrote: > Hi all, > > As we all know, the data node does not store all the block files in the same > directory but instead creates appropriate subdirectories. I am trying to > know how can one get to know this subdirectory name ? > > I have a java program that takes a filename and gets the list of blocks that > make up the file and the list of hosts that host each of these blocks. Now I > need to know the subdirectory (if any) where the block is stored on a given > host. > > This is my program so far: > > class LocateBlocks { > public static void main(String[] args) throws Exception { > if(args.length != 1) { > System.out.println("error"); > System.exit(1); > } > // filename. > String fileName = args[0]; > > // configuration object. > Configuration conf = new Configuration(); > > // get the DistributedFileSystem object. > DistributedFileSystem fs = (DistributedFileSystem) > FileSystem.get(URI.create(fileName), conf); > > // get the corresponding DFSClient object. > DFSClient client = fs.getClient(); > > // get the namenode. > ClientProtocol nameNode = client.namenode; > > // get file info. > HdfsFileStatus fStatus = nameNode.getFileInfo(fileName); > > // get file size. > long fSize = fStatus.getLen(); > > // get block location information. > LocatedBlocks locBlks = > nameNode.getBlockLocations(fileName,0,fSize); > > // get a list of blocks for this file. > List<LocatedBlock> locBlkList = locBlks.getLocatedBlocks(); > > // iterate over the list of blocks. > System.out.println(locBlkList.size()); > for(LocatedBlock lBlk : locBlkList) { > > // get block name. > Block blk = lBlk.getBlock(); > String blkName = blk.getBlockName(); > > // foreach block get the array of hostnames on which the block > resides. > DatanodeInfo[] dNodes = lBlk.getLocations(); > System.out.println(dNodes.length); > System.out.println(blkName); > for(DatanodeInfo dNode: dNodes) { > String hostName = dNode.getHostName(); > > System.out.println(hostName); > } > } > } > } > > Thanks
