云数据库 GAUSSDB-案例：设置cost_param对查询性能优化:现象描述2

时间：2024-01-23 20:09:36

云数据库 GAUSSDB

现象描述2

当cost_param的bit1(set cost_param=2)为1时，表示求多个过滤条件（Filter）的选择率时，选择最小的作为总的选择率，而非两者乘积，此方法在过滤条件的列之间关联性较强时估算更加准确。下面查询的例子是cost_param的bit1为1时的优化场景。

表结构如下所示：

  
   
     
     
       CREATE TABLE NATION
(
  N_NATIONKEY INT NOT NULL
, N_NAME      CHAR(25) NOT NULL
, N_REGIONKEY INT NOT NULL
, N_COMMENT   VARCHAR(152)
) distribute by replication;
CREATE TABLE SUPPLIER
(
  S_SUPPKEY   BIGINT NOT NULL
, S_NAME      CHAR(25) NOT NULL
, S_ADDRESS   VARCHAR(40) NOT NULL
, S_NATIONKEY INT NOT NULL
, S_PHONE     CHAR(15) NOT NULL
, S_ACCTBAL   DECIMAL(15,2) NOT NULL
, S_COMMENT   VARCHAR(101) NOT NULL
) distribute by hash(S_SUPPKEY);
CREATE TABLE PARTSUPP
(
  PS_PARTKEY    BIGINT NOT NULL
, PS_SUPPKEY    BIGINT NOT NULL
, PS_AVAILQTY   BIGINT NOT NULL
, PS_SUPPLYCOST DECIMAL(15,2)NOT NULL
, PS_COMMENT    VARCHAR(199) NOT NULL
)distribute by hash(PS_PARTKEY);

      

    

  
 

查询语句如下所示：

  
   
     
     
       set cost_param=2;
explain verbose select
nation,
sum(amount) as sum_profit 
from
(
select
n_name as nation,
l_extendedprice * (1 - l_discount) - ps_supplycost * l_quantity as amount
from
supplier,
lineitem,
partsupp,
nation
where
s_suppkey = l_suppkey
and ps_suppkey = l_suppkey
and ps_partkey = l_partkey
and s_nationkey = n_nationkey
) as profit 
group by nation 
order by nation;

      

    

  
 