为什么在mySql过程执行中有执行时间的模式

Question

我有一个存储过程可以在 mySql 中生成一些输出。

BEGIN
  START TRANSACTION;

  CREATE TEMPORARY TABLE IF NOT EXISTS tempDays
  (
    ID int AUTO_INCREMENT PRIMARY KEY,
    -- column list

  );
 CREATE TEMPORARY TABLE IF NOT EXISTS tempPeriods
  (
    ID int AUTO_INCREMENT PRIMARY KEY,
    -- column list

  );
  INSERT INTO tempDays (-- column list) SELECT -- select list contains n number of rows with some conditions
--
--
-- some queries and temporary table creation
--
--
--
  SELECT COUNT(*) INTO @daylimit FROM tempDays;
  SELECT 1 INTO @daycounter;

  WHILE(@daycounter<=@daylimit)
  DO

       SELECT COUNT(*) INTO @limitperiods FROM tempPeriods;
    SELECT 1 INTO @countperiods;

      WHILE(@countperiods<=@limitperiods)
      DO
         -- some complicated(some sort of IF THEN blocks to take time some execution time) query inside.
          SET @countperiods=@countperiods+1;
      END WHILE;
  SET @daycounter=@daycounter+1;
  END WHILE;

  SELECT * FROM temptimetable;
  TRUNCATE TABLE tempDays;
  TRUNCATE TABLE tempPeriods;
 END TRANSACTION;
END 

这是8个一一调用的执行总结。

Stored procedure 'sample_db.sample_proc' has been executed in 1.565s.
Stored procedure 'sample_db.sample_proc' has been executed in 2.362s.
Stored procedure 'sample_db.sample_proc' has been executed in 1.541s.
Stored procedure 'sample_db.sample_proc' has been executed in 2.198s.
Stored procedure 'sample_db.sample_proc' has been executed in 1.863s.
Stored procedure 'sample_db.sample_proc' has been executed in 3.657s.
Stored procedure 'sample_db.sample_proc' has been executed in 2.306s.
Stored procedure 'sample_db.sample_proc' has been executed in 3.226s.

我们可以看到一个执行时间模式... 1,2,1,2,3,2,3

你能解释一下是否有任何与执行时间相关的东西取决于之前的执行。 我发现一个是，不需要重新创建临时表会导致执行时间减少。 但是如果再次执行它，我们可以看到执行时间增加。 如何？ 这是执行图..

Answer 1

时间不是最好的绩效衡量标准。 这可能是由于与您的存储过程没有直接关系的各种因素造成的：IO、内存授予等。特别是考虑到相对较短的运行时间。

您必须能够查看 mysql io 操作的内容、查询的执行计划等，才能确定到底发生了什么。