Mysql存储过程优化——使用临时表代替游标

Mysql游标在操作小数据量时比较方便，效率可观，但操作大数据量，速度比较慢，甚至直接产生系统错误。

 

一般说来，当操作的数据超过1万条时，就避免用游标吧。

 

为了测试游标性能，写了下面一个游标对IDC_Gather_Info表中数据进行遍历

CREATE DEFINER=`root`@`%` PROCEDURE `debug`(IN `beginTime` int, IN `checkTime` int)
BEGIN
	DECLARE t_id VARCHAR(64) DEFAULT '';
	DECLARE t_item TINYINT DEFAULT 0;
	DECLARE t_result VARCHAR(8192) DEFAULT '';

	DECLARE cursorDone INT DEFAULT 0;
	DECLARE cur CURSOR FOR SELECT Asset_Id, Check_Item, Check_Result from IDC_Gather_Info WHERE Check_Time > beginTime AND Check_Time <= checkTime;
	DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET cursorDone = 1;

	OPEN cur;
	cursorLoop:LOOP
		FETCH cur INTO t_id, t_item, t_result;
		IF cursorDone = 1 THEN
			LEAVE cursorLoop;
		END IF;
	END LOOP;
	CLOSE cur;
END

下面是当表中数据分别为15万、5万、1万时游标的表现：

 

1.数据量15万，存储过程执行失败，提示错误：Incorrect key file for table '/tmp/#sql_3044_0.MYI';try to repair it

2.数据量5万，执行成功，耗时31.051s

3.数据量1万，执行成功，耗时1.371s

 

下面使用临时表替换游标：

CREATE DEFINER=`root`@`%` PROCEDURE `debug`(IN `beginTime` int, IN `checkTime` int)
BEGIN
	DECLARE t_id VARCHAR(64) DEFAULT '';
	DECLARE t_item TINYINT DEFAULT 0;
	DECLARE t_result VARCHAR(8192) DEFAULT '';
	
	DECLARE maxCnt INT DEFAULT 0;
	DECLARE i INT DEFAULT 0;

	DROP TABLE IF EXISTS Gather_Data_Tmp;
	CREATE TEMPORARY TABLE Gather_Data_Tmp(
		`Tmp_Id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
		`Asset_Id` VARCHAR(16) NOT NULL,
		`Check_Item` TINYINT(1) NOT NULL,
		`Check_Result` VARCHAR(8192) NOT NULL,
		PRIMARY KEY (`Tmp_Id`)
	)ENGINE=MyISAM DEFAULT CHARSET=utf8;

	SET @tSql = CONCAT('INSERT INTO Gather_Data_Tmp (`Asset_Id`, `Check_Item`, `Check_Result`) 
											SELECT Asset_Id, Check_Item, Check_Result 
											FROM IDC_Gather_Info 
											WHERE Check_Time > ',beginTime,' AND Check_Time <= ',checkTime);
	PREPARE gatherData FROM @tSql;
	EXECUTE gatherData;

	SELECT MIN(`Tmp_Id`) INTO i FROM Gather_Data_Tmp;
	SELECT MAX(`Tmp_Id`) INTO maxCnt FROM Gather_Data_Tmp;

	WHILE i <= maxCnt DO
		SELECT Asset_Id, Check_Item, Check_Result INTO t_id, t_item, t_result FROM Gather_Data_Tmp WHERE Tmp_Id = i;
		SET i = i + 1;
	END WHILE;
END

 

1.数据量15万，执行成功，耗时8.928s

2.数据量5万，执行成功，耗时2.994s

3.数据量1万，执行成功，耗时0.634s

 

可以看到Mysql的游标在处理大一点的数据量时还是比较乏力的，仅适合用于操作几百上千的小数据量。