Block类图描述

前面2个描述了datanode以及INodeFile，还缺个Block的描述，这里补上，针对block的结构还有些不是特别明确，这个需要举例子才好说明，先把大体的类图结构描述下

 

    Block

 

/**************************************************
 * A Block is a Hadoop FS primitive, identified by a 
 * long.
 *
 **************************************************/

 

    BlocksMap

 

 

/**
 * This class maintains the map from a block to its metadata.
 * block's metadata currently includes INode it belongs to and
 * the datanodes that store the block.
 */

 

     BlockInfo

 

 

/**
   * Internal class for block metadata.
   */

 

    Object[] triplets

 

 

    /**
     * This array contains triplets of references.
     * For each i-th data-node the block belongs to
     * triplets[3*i] is the reference to the DatanodeDescriptor
     * and triplets[3*i+1] and triplets[3*i+2] are references 
     * to the previous and the next blocks, respectively, in the 
     * list of blocks belonging to this data-node.
     */