2016/10/19

MapReduce的过程：把原来的数据分成块，一条一条记录使用MAP函数生成键值对，以键值把把键值对归类形成集合，再把这些集合进行排序。
开发者定义四个过程：输入-》键值对，MAP,REDUCE,键值对=》输出

炼数成金

• hadoop不是数据库，因为它不提供数据库的基本功能

- **hadoop不适用实时计算，因为有时间差？什么是实时计算？分析股票行情出发一些动作，红绿灯调度问题

Pro Apache Hadoop

• namenode:metadata
• Configuration file
  
  • default file and site file
  -
• secondary namenode: not backup, housekeeping
  
  • merge edit and fsimage
  • edits: accumulate the change since the last changepoint
  • fsimage:last checkpoing
  • fstime: contains the timestamp of the last checkpoint
• Task Tracker:
  
  • accepts requests for task such as map, reduce ad shuffle
  • slota= cores on the machine
  • ???多处理器和多核的区别???
  • hearbeat: tell whether healthy and how many free slots are available
• Job Tracker:
  
  • schedule: close to the data block
  • determin number of taks
• YERN
  
  • the idea is to have a global resource manager and a per-application Application Master.
  • components
    
    • global resouece mannager
      
      • primaly a schedular
      • ensure uptimal cluster utilization
    • node manager
      
      • local resource manager
      • slave service.
      • take requests form resource manager and allocates containers to application
      • eachnode has its own node manager
    • application-specific application master
      
      • is the key defferentiatorbetween the older MapReduce v1 framework and YARN
      • each type has an application master
      • improved scalability
      • a more generic framework
    • scheduler
    • container
      
      • CPU and memory
    -