Postgres 存储过程为多次调用 now() 返回相同的纪元

Question

我写了一段代码来使用下面的存储过程获取过程调用的执行时间。但问题是输出显示 start_time 和 end_time 具有相同的纪元值，因此 execution_time 总是返回 0。你能帮我看看为什么我得到相同的纪元值吗调用 now() ?

CREATE OR REPLACE PROCEDURE public.calculate_execution_time()
LANGUAGE plpgsql
AS $procedure$
    DECLARE
        start_time float;
        end_time float;
    BEGIN
        SELECT extract(epoch from now()) into start_time;
        call public.another_stored_procedure();
        SELECT extract(epoch from now()) into end_time;
        raise notice 'Execution time = % - % = % seconds', end_time, start_time, (end_time - start_time);
    END;
$procedure$
;

示例输出： call public.calculate_execution_time()

Execution time = 1620213218.485702 - 1620213218.485702 = 0 seconds

Answer 1

具有now() return 固定时间（事务开始时）被认为是一项功能而不是错误。它实际上对长运行存储过程很方便。

您需要 clock_timestamp()：

BEGIN
    SELECT extract(epoch from clock_timestamp) into start_time;
    call public.another_stored_procedure;
    SELECT extract(epoch from clock_timestamp) into end_time;
    raise notice 'Execution time = % - % = % seconds', end_time, start_time, (end_time - start_time);
END;

Postgres 存储过程为多次调用 now() 返回相同的纪元

Postgres stored procedure returning same epoch for multiple calls to now()

sql

postgresql

stored-procedures

plpgsql

execution-time