為什么在mySql過程執行中有執行時間的模式

Question

我有一個存儲過程可以在 mySql 中生成一些輸出。

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 

這是8個一一調用的執行總結。

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.

我們可以看到一個執行時間模式... 1,2,1,2,3,2,3

你能解釋一下是否有任何與執行時間相關的東西取決於之前的執行。 我發現一個是，不需要重新創建臨時表會導致執行時間減少。 但是如果再次執行它，我們可以看到執行時間增加。 如何？ 這是執行圖..

Answer 1

時間不是最好的績效衡量標准。 這可能是由於與您的存儲過程沒有直接關系的各種因素造成的：IO、內存授予等。特別是考慮到相對較短的運行時間。

您必須能夠查看 mysql io 操作的內容、查詢的執行計划等，才能確定到底發生了什么。