Hadoop中的FileStatus、BlockLocation、LocatedBlocks、InputSplit

深碍√TFBOYSˉ_ 2021-09-26 02:16 219阅读 0赞

# 1 FileStatus #

**1.1 包名**  
org.apache.hadoop.fs.FileStatus

**1.2 格式**

FileStatus\{path=hdfs://192.X.X.X:9000/hadoop-2.7.1.tar.gz; isDirectory=false; length=210606807; replication=3; blocksize=134217728; modification\_time=xxx; access\_time=xxx; owner=xxx; group=supergroup; permission=rw-r--r--; isSymlink=false\}

# 2 BlockLocation #

**2.1 包名**  
org.apache.hadoop.fs.BlockLocation

**2.2 调用处**  
JobClient的writeNewSplits方法，其中调用了List<InputSplit> splits = input.getSplits(job)方法，在getSplits方法中调用了getFileLocation()。

**2.3 格式**

public static void getFileLocation() throws Exception {
        Configuration conf = new Configuration();
    	Path fpath = new Path(AConstants.hdfsPath + "hadoop-2.7.1.tar.gz");
    	FileSystem hdfs = fpath.getFileSystem(conf);
    	FileStatus filestatus = hdfs.getFileStatus(fpath);
    	BlockLocation[] blkLocations = hdfs.getFileBlockLocations(filestatus,0, filestatus.getLen());
    	System.out.println("total block num:" + blkLocations.length);
    	for (int i = 0; i < blkLocations.length; i++) {
    		System.out.println(blkLocations[i].toString());
    		System.out.println("文件在block中的偏移量" + blkLocations[i].getOffset()
                    + ", 长度" + blkLocations[i].getLength());
    	}
    }

total block num:2  
0,134217728,192.X.X.X  
文件在block中的偏移量0, 长度134217728  
134217728,76389079,192.X.X.X  
文件在block中的偏移量134217728, 长度76389079

**splits数组信息**

int blkIndex = getBlockIndex(blkLocations, length-bytesRemaining);
    splits.add(makeSplit(path, length-bytesRemaining,
    splitSize,blkLocations[blkIndex].getHosts(),blkLocations[blkIndex].getCachedHosts()));

\[hdfs://192.x.x.x:9000/hadoop-2.7.1.tar.gz:0+134217728,   
hdfs://192.x.x.x:9000/hadoop-2.7.1.tar.gz:134217728+31987190\]

# 3 LocatedBlocks #

**3.1 包名**  
org.apache.hadoop.hdfs.protocol.LocatedBlocks

**3.2 调用处**  
在hdfs读取文件时调用openInfo()方法，最终调用的是DFSInputStream的**fetchLocatedBlocksAndGetLastBlockLength**方法获取块信息LocatedBlocks。块的信息非常详尽，如块名称，大小，起始偏移量，IP地址等。

在hadoop中写文件实际是把block写入到datanode中，而namenode是通过datanode定期的汇报得知该文件到底由哪几个block组成的。因此在读某个文件时可能存在datanode还未汇报给namenode的情况，因此在读文件时只能读到最后一个汇报的block块。**isLastBlockComplete**可以标识是否读取到最后的块。若不是则会根据元数据提供的block的pipeline来到datanode上获得block的写入长度，并赋值给lastBlockBeingWrittenLength。

**3.3 格式**

LocatedBlocks {
    	fileLength = 210606807
    		underConstruction = false
    		blocks = [LocatedBlock {
    				BP - 1853423215 - 192.X.X.X - 1474747765776: blk_1073741828_1004;
    				getBlockSize() = 134217728;
    				corrupt = false;
    				offset = 0;
    				locs = [192.X.X.X: 50010]
    			}, LocatedBlock {
    				BP - 1853423215 - 192.X.X.X - 1474747765776: blk_1073741829_1005;
    				getBlockSize() = 76389079;
    				corrupt = false;
    				offset = 134217728;
    				locs = [192.X.X.X: 50010]
    			}
    		]
    		lastLocatedBlock = LocatedBlock {
    		BP - 1853423215 - 192.X.X.X - 1474747765776: blk_1073741829_1005;
    		getBlockSize() = 76389079;
    		corrupt = false;
    		offset = 134217728;
    		locs = [192.X.X.X: 50010]
    	}
    	isLastBlockComplete = true
    }