VastbaseG100

嵌套循环并行查询

功能描述

嵌套循环并行查询是利用多核CPU的并行处理，将一个表连接语句由多个并行worker线程执行。

示例

创建两张表：

create table t1(a int,b int,c int,d bigint);
create table t2(a int,b int);

插入数据并分析表：

insert into t1 values 
(generate_series(1,100),generate_series(1,10),generate_series(1,2),generate_series(1,50))；
insert into t2 values(generate_series(1,100),generate_series(1,30));
analyze t1;
analyze t2;

设置算子并行度和表连接代价开关：

set query_drop=2;
set enable_nestloop=on;
set enable_mergejoin=off;
set enable_hashjoin=off;

打印嵌套循环并行查询计划

explain (costs off) select t1.a,t2.b from t1,t2 where t1.a=t2.a order by 1,2;