Hive mapjoin的执行计划解读

创建两张表，以emp表和dept表为例：

create table emp(
empno int, 
ename string, 
job string, 
mgr int, 
hiredate string, 
sal double, 
comm double, 
deptno int
)row format delimited fields terminated by '\t';

加载数据：

load data local inpath '/home/hadoop/data/emp.txt' overwrite into table emp; 

CREATE TABLE dept(
deptno int,
dname string,
loc string
)row format delimited fields terminated by '\t';

加载数据：

load data local inpath '/home/bigdata/testdata/dept.txt' overwrite into table dept;

执行计划解读：

首先设置set hive.auto.convert.join=false;Hive默认是true

explain select  e.empno, e.ename, d.dname from emp e join dept d on e.deptno=d.deptno;	

输出信息如下：

STAGE DEPENDENCIES:
  Stage-1 is a root stage
  Stage-0 depends on stages: Stage-1

STAGE PLANS:
  Stage: Stage-