HDFS centralized cache management

本文主要是介绍HDFS centralized cache management，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

Hadoop 2.3.0解决了如下几个问题：

可以指定自己的热点数据常存内存；
NameNode manage centralized cache;
without DataNode OS buffer cache to saving resoureces;
speed up HDFS client read .when the block cache in memory ,directly using zero-copy read from cache pass thougth hard I/O、checksum.

下面内容是参考

cache directive: 表示要被cache到内存的文件或者目录。
cache pool: 用于管理一系列的cache directive，类似于命名空间

具体操作：

[root@HDP01 ~]# 
[root@HDP01 ~]# hdfs cacheadmin -addPool financial
AccessControlException: Access denied for user root. Superuser privilege is required
[root@HDP01 ~]# 
[root@HDP01 ~]# su hdfds
su: user hdfds does not exist
[root@HDP01 ~]# su hdfs
[hdfs@HDP01 root]$ hdfs cacheadmin -addPool financial
Successfully added cache pool financial.
[hdfs@HDP01 root]$ exit
exit
[root@HDP01 ~]# hdfs cacheadmin -addDirective -path /test/install.log -pool financial -replication 1
AccessControlException: Permission denied while accessing pool financial: user root does not have WRITE permissions.
[root@HDP01 ~]# 
[root@HDP01 ~]# su hdfs
[hdfs@HDP01 root]$ hdfs cacheadmin -addDirective -path /test/install.log -pool financial -replication 1
Added cache directive 1
[hdfs@HDP01 root]$ 
[hdfs@HDP01 root]$ hdfs cacheadmin -listPools
Found 1 result.
NAME       OWNER  GROUP   MODE            LIMIT  MAXTTL
financial  hdfs   hadoop  rwxr-xr-x   unlimited   never
[hdfs@HDP01 root]$ 
[hdfs@HDP01 root]$ hdfs cacheadmin -listPools
Found 1 result.
NAME       OWNER  GROUP   MODE            LIMIT  MAXTTL
financial  hdfs   hadoop  rwxr-xr-x   unlimited   never
[hdfs@HDP01 root]$ 
[hdfs@HDP01 root]$ hdfs cacheadmin -listDirectives
Found 1 entryID POOL        REPL EXPIRY  PATH              1 financial      1 never   /test/install.log 
[hdfs@HDP01 root]$

centralized cache和distributed cache的区别：