hadoop版本更新比较慢，做些记录。
3.0主要更新功能：
hdfs erasure coding ，最早由twitter提出，类似于软RAID功能，可以节省1.5倍存储空间，使用于存储鸡肋数据场景，重要数据重构需要一定ＣＰＵ，除非群体有大量空间时间。
YARN Timeline Service，MapReduce 1阶段，和JobTracker集成在一块，大集群写日志消耗较大，到MapReduce 2阶段，相应功能迁移到historyserver，存在SPOF问题，这一版本还是试验性质。
Support for Opportunistic Containers and Distributed Scheduling: 低priority container
Support for more than 2 NameNodes: 单个namenode->Active/Standby namenode->multiple
Intra-datanode balancer：这个功能比较不错，单机多磁盘balancer，老版本经常有这个问题。
YARN Resource Types：受linux cgroup限制，老版本只支持CPU和Memory，这个版本终于支持GPU了，还没看底层实现。
3.1主要更新：
Yarn Service framework provides first class support and APIs to host long running services natively in YARN.
In a nutshell, it serves as a container orchestration platform for managing containerized services on YARN. It supports both docker container and traditional process based containers in YARN. 加强对Docker Container支撑
First-class GPU scheduling and isolation (For both docker/non-docker containers) on YARN.
First-class FPGA scheduling and isolation (For both docker/non-docker containers) on YARN
PB级数据AI的支撑，TB级有Dask足够。
Support administrators to specify absolute resources (X Memory, Y VCores, Z GPUs, etc.) to a queue instead of providing percentage based values. This provides better control for admins to configure required amount of resources for a given queue.
Hadoop 1 Memory(Java Process实现)=> Hadoop 2 Memory+CPU (Linux CGroup实现)=>Hadoop 3 Memory+CPU + GPU
PB级机器学习和深度学习，Hadoop 3.1首选。
