分区导入数据性能优化

场景描述

当向分区表插入数据的时候，如果插入的数据为常量/参数/表达式等简单类型，会自动对INSERT算子进行执行优化（FastPath）。可以通过执行计划来判断是否触发了执行优化，触发执行优化时Insert计划前会带有FastPath关键字。

示例

gaussdb=# 
CREATE TABLE fastpath_t1
(
    col1 INT,
    col2 TEXT
) 
PARTITION BY RANGE(col1)
(
    PARTITION p1 VALUES LESS THAN(10),
    PARTITION p2 VALUES LESS THAN(MAXVALUE)
);

--INSERT常量，执行FastPath优化
gaussdb=# EXPLAIN INSERT INTO fastpath_t1 VALUES (0, 'test_insert');
                            QUERY PLAN                            
------------------------------------------------------------------
 FastPath Insert on fastpath_t1  (cost=0.00..0.01 rows=1 width=0)
   ->  Result  (cost=0.00..0.01 rows=1 width=0)
(2 rows)

--INSERT带参数/简单表达式，执行FastPath优化
gaussdb=# PREPARE insert_t1 AS INSERT INTO fastpath_t1 VALUES($1 + 1 + $2, $2);
PREPARE
gaussdb=# EXPLAIN EXECUTE insert_t1(10, '0');
                            QUERY PLAN                            
------------------------------------------------------------------
 FastPath Insert on fastpath_t1  (cost=0.00..0.02 rows=1 width=0)
   ->  Result  (cost=0.00..0.02 rows=1 width=0)
(2 rows)

--INSERT为子查询，无法执行FastPath优化，走标准执行器模块
gaussdb=# CREATE TABLE test_1(col1 int, col3 text);
gaussdb=# EXPLAIN INSERT INTO fastpath_t1 SELECT * FROM test_1;
                           QUERY PLAN                            
-----------------------------------------------------------------
 Insert on fastpath_t1  (cost=0.00..22.38 rows=1238 width=36)
   ->  Seq Scan on test_1  (cost=0.00..22.38 rows=1238 width=36)
(2 rows)

gaussdb=# DROP TABLE fastpath_t1;
gaussdb=# DROP TABLE test_1;