５。hbase高级部分 - Coprocessor (vs Filter)

?what

  in a SQL DB Server,in tradictionally,contains Triggers or Procedures,and the privior is used to handle server's internal transactions,most of 'post-do' operations;the laster also is subroutine to processs 'client-server' interactive ops.

 

?why

     just same like with it,HBase has it's internal computation framework named Coprocessor(CP) to play thes e funcs.similar to Scan,this CP is placed in server end,but diffenerce by Reduce the huge data returned to client.

  within CP,users can interact with hbase more neatly.

 

?how

CP VS Filter implemetion

type	triggered by	customed	executed at	appliations
Filter	client	client	server	scan,simple count by client
Observer	master/region/wal	server	server	secondary index,access control, complex filter
Endpoint	client	client	server	aggregate functions,sum,max...

 

common coprocessor flow:

 

EndPoint coprocessor flow:

 

可以看到,client是以region 为单位访问的,这意味着一个rs上太多regions的话,在全表统计时将产生很多连接请求.其实类似我们在solr实现一样,可以merge-in-rs即可 TODO

 

?features

1 advantages

 -reduce much data to client to computation

 -converient intersactions to hbase

 

2 disvantages

 -just slimilar to common SQL DB,if this CPs are CPU ,MEM or IO intensive,this will slow down the entire cluster performance.so i think if you are run in thise case,let the cluster to in a off-line state is much better.

 -CP is different from Bigtable's one,the former is a plugin in hbase,and the later is a individual process out of server,so this may impact server to run normally.

 

 另外在看HRegion#exec()时发现

CoprocessorProtocol handler = protocolHandlers.getInstance(protocol);

 这意味着一个protocol只有一个implement,通常这没什么问题,但是需要知道的