String message= String.format("读取文件 : [%s] 时出错,请确认文件:[%s]存在且配置的用户有权限读取", filepath, filepath);throwDataXException.asDataXException(HdfsReaderErrorCode.READ_FILE_ERROR, message, e); } }publicvoidsequenceFileStartRead(String sourceSequenceFilePath, Configuration readerSliceCo...
Client调用DistributedFileSystem对象的create方法,创建一个文件输出流(FSDataOutputStream)对象 通过DistributedFileSystem对象与Hadoop集群的NameNode进行一次RPC远程调用,在HDFS的Namespace中创建一个文件条目(Entry),该条目没有任何的Block 通过FSDataOutputStream对象,向DataNode写入数据,数据首先被写入FSDataOutputStream对象内部的Bu...
HDFS具备高容错性（fault-tolerant）的特点，并且设计用来部署在低廉的（low-cost）硬件上。而且它提供高...
The following video walks through file read and write operations in HDFS. Figure 3: File reads in HDFSFigure 3 illustrates the process of a file read in HDFS. An HDFS client (the entity that needs to access a file) first contacts the NameNode when a file is opened for reading. The ...
HDFS: hadoop distributed file system 它抽象了整个集群的存储资源,可以存放大文件。 文件采用分块存储复制的设计。块的默认大小是64M。 流式数据访问,一次写入(现支持append),多次读取。 不适合的方面: 低延迟的数据访问 解决方案:HBASE 大量的小文件
a file do not evenly distribute across the racks. One third of replicas are on one node, two thirds of replicas are on one rack, and the other third are evenly distributed across the remaining racks. This policy improves write performance without compromising data reliability or read performance...
it.FSDataOutputStreamout=fileSystem.create(path);InputStreamin=newBufferedInputStream(newFileInputStream(newFile(source)));byte[]b=newbyte[1024];intnumBytes=0;while((numBytes=in.read(b))>0){out.write(b,0,numBytes);}// Close all the file descriptersin.close();out.close();fileSystem.close(...
构造DFSInputStream对象时,调用namenode的getBlockLocation方法,获得file开始的若干个block的存储datanode列表;针对每个block的dn列表,会根据网络拓扑排序,离client近的排在前面。 调用DFSInputStream的read方法读取blk1的数据,与client最近的datanode建立连接,读取数据。
INodeFileUnderConstruction newNode =dir.addFile(src, permissions, replication, blockSize, holder, clientMachine,clientNode, genstamp); // 创建一个新的文件,状态为under construction,没有任何data block与之对应 4、然后客户端向新创建的文件中写入数据,一般会使用FSDataOutputStream的write函数,最终会调用DFSOut...
tSize num_written_bytes = hdfsWrite(fs, writeFile, (void*)buffer, strlen(buffer)+1); fprintf(stderr, "Wrote %d bytes\n", num_written_bytes); 打开文件进行写。 const char* readPath = "/tmp/testfile.txt"; int exists = hdfsExists(fs, readPath); ...