Examples of org.apache.hadoop.dfs.DataNode$DataNodeMetrics

org.apache.hadoop.dfs.DataNode

DataNode is a class (and program) that stores a set of blocks for a DFS deployment. A single deployment can have one or many DataNodes. Each DataNode communicates regularly with a single NameNode. It also communicates with client code and other DataNodes from time to time. DataNodes store a series of named blocks. The DataNode allows client code to read these blocks, or to write new block data. The DataNode may also, in response to instructions from its NameNode, delete blocks or copy blocks to/from other DataNodes. The DataNode maintains just one critical table: block-> stream of bytes (of BLOCK_SIZE or less) This info is stored on a local disk. The DataNode reports the table's contents to the NameNode upon startup and every so often afterwards. DataNodes spend their lives in an endless loop of asking the NameNode for something to do. A NameNode cannot connect to a DataNode directly; a NameNode simply returns values from functions invoked by a DataNode. DataNodes maintain an open server socket so that client code or other DataNodes can read/write data. The host/port for this server is reported to the NameNode, which then sends that information to clients or other DataNodes that might be interested. @author Mike Cafarella


      // start a third datanode
      cluster.startDataNodes(conf, 1, true, null, null);
      ArrayList<DataNode> datanodes = cluster.getDataNodes();
      assertEquals(datanodes.size(), 3);
      DataNode dataNode = datanodes.get(2);
      
      // report corrupted block by the third datanode
      cluster.getNameNode().namesystem.markBlockAsCorrupt(blk, 
          new DatanodeInfo(dataNode.dnRegistration ));

Examples of org.apache.hadoop.dfs.DataNode$DataNodeMetrics

Related Classes of org.apache.hadoop.dfs.DataNode$DataNodeMetrics