postgres的自定义函数没有上下文切换开销？

显示全部楼层 · 2012-5-21 10:19:41

test=# \timing
Timing is on.
--用内置round函数
test=# select avg(round(a)) from generate_series(1,1000000) a;
avg
----------
500000.5
(1 row)
Time: 208.583 ms
test=# select avg(round(a)) from generate_series(1,10000000) a;
avg
-----------
5000000.5
(1 row)
Time: 1971.878 ms (00:01.972)
--用自定义函数，实际再调用round函数
test=# create or replace function myround(a int) returns double precision
test-# as $$
test$# select round(a);
test$# $$
test-# language sql;
CREATE FUNCTION
Time: 2.227 ms
test=# select avg(myround(a)) from generate_series(1,1000000) a;
avg
----------
500000.5
(1 row)
Time: 200.740 ms
test=# select avg(myround(a)) from generate_series(1,10000000) a;
avg
-----------
5000000.5
(1 row)
Time: 2048.413 ms (00:02.048)

千问 · 2012-5-21 10:19:41

系统内置的是3个重载函数
test=# \df round

List of functions
Schema | Name| Result data type | Argument data types | Type
------------+-------+------------------+---------------------+------
pg_catalog | round | double precision | double precision| func
pg_catalog | round | numeric
| numeric
| func
pg_catalog | round | numeric
| numeric, integer| func
(3 rows)