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mysql cpu 占比过高问题解决_mysql占用cpu特别高的解决

作者：小小林熬夜学编程 | 2024-05-17 10:23:01

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mysql占用cpu特别高的解决
  • 1 首先我们找到mysql占比高的进程号PID <ps 我这里已经优化过了 所以占比较低>
top

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在这里插入图片描述

  • 2 根据PID找到mysql的os_thread_id
 top -H -p 2559

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在这里插入图片描述
我们这里可以明显看到有个pid=16815的程序在占用cpu进程 那么我们找到这进行查询的慢sql
这里可以看到是哪个主机连接的信息

SELECT
	a. USER,
	a. HOST,
	a.db,
	b.thread_os_id,
	b.thread_id,
	a.id processlist_id,
	a.command,
	a.time,
	a.state,
	a.info
FROM
	information_schema. PROCESSLIST a,
	PERFORMANCE_SCHEMA .threads b
WHERE
	a.id = b.processlist_id
AND b.thread_os_id = 16804;

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在这里插入图片描述

  • 我们最终要的是sql 那么执行下面找个就可以找到高id的进程所属的sql
SELECT
	*
FROM
	PERFORMANCE_SCHEMA.events_statements_current
WHERE
	thread_id = (
		SELECT
			thread_id
		FROM
			PERFORMANCE_SCHEMA .threads
		WHERE
			thread_os_id = 16804
	) ;

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在这里插入图片描述
接下来优化sql就行了

这里我们随意找一处比较耗时的sql来做统计
这应该是一位非常懂这块业务的哥们写的 我们来看一下

EXPLAIN
SELECT g.*
FROM (
	SELECT DISTINCT ru.id AS unitId, ru.unit_name AS unitName, ru.create_time, ru.baseid, ru.entid
		, p.id AS postId, p.post_name AS postName, IFNULL(a.patrolNum, 0) AS patrolNum
		, IFNULL(ht.hiddenNum, 0) AS hiddenNum, b.postRiskLevel
		, b.postRiskLevelText, c.unitRiskLevel, c.unitRiskLevelText
	FROM drh_risk_unit_post rup
		LEFT JOIN drh_risk_unit ru ON ru.id = rup.risk_unit_id
		LEFT JOIN ent_post p ON p.id = rup.post_id
		LEFT JOIN (
			SELECT COUNT(1) AS patrolNum, pp.post_id
			FROM drh_post_patrol pp
			GROUP BY pp.post_id
		) a
		ON a.post_id = rup.post_id
		LEFT JOIN (
			SELECT COUNT(1) AS hiddenNum, h.post_id
			FROM drh_hidden h
			GROUP BY h.post_id
		) ht
		ON ht.post_id = rup.post_id
		LEFT JOIN (
			SELECT llt.*, dt.item_text AS postRiskLevelText
			FROM (
				SELECT ht1.*
				FROM (
					SELECT a.*, rup.risk_unit_id
					FROM drh_risk_unit_post rup
						LEFT JOIN (
							SELECT MIN(hft.risk_level) AS postRiskLevel, pr.post_id
							FROM (
								SELECT hf.fk_id, MIN(hf.risk_level) AS risk_level
								FROM drh_post_result_hazar_factors hf
								GROUP BY hf.fk_id
							) hft
								LEFT JOIN drh_post_result pr ON pr.id = hft.fk_id
							WHERE pr.post_id IS NOT NULL
							GROUP BY pr.post_id
						) a
						ON a.post_id = rup.post_id
						LEFT JOIN drh_risk_unit ru ON ru.id = rup.risk_unit_id
					WHERE ru.unit_source = '1'
				) ht1
				UNION ALL
				SELECT ht2.*
				FROM (
					SELECT a.*, rup.risk_unit_id
					FROM drh_risk_unit_post rup
						LEFT JOIN (
							SELECT MIN(hft.risk_level) AS postRiskLevel, sm.post_id
							FROM (
								SELECT hf.fk_id, MIN(hf.risk_level) AS risk_level
								FROM drh_post_result_hazar_factors hf
								GROUP BY hf.fk_id
							) hft
								LEFT JOIN drh_safety_matters sm ON sm.id = hft.fk_id
							WHERE sm.post_id IS NOT NULL
							GROUP BY sm.post_id
						) a
						ON a.post_id = rup.post_id
						LEFT JOIN drh_risk_unit ru ON ru.id = rup.risk_unit_id
					WHERE ru.unit_source = '2'
				) ht2
			) llt
				LEFT JOIN sys_dict_item dt ON llt.postRiskLevel = dt.item_value
				LEFT JOIN sys_dict d ON dt.dict_id = d.id
			WHERE d.dict_code = 'drh_inherent_risk_level'
		) b
		ON b.risk_unit_id = rup.risk_unit_id
			AND b.post_id = rup.post_id
		LEFT JOIN (
			SELECT tll.*, dt.item_text AS unitRiskLevelText
			FROM (
				SELECT ull.risk_unit_id, MIN(ull.postRiskLevel) AS unitRiskLevel
				FROM (
					SELECT ht1.*
					FROM (
						SELECT a.*, rup.risk_unit_id
						FROM drh_risk_unit_post rup
							LEFT JOIN (
								SELECT MIN(hft.risk_level) AS postRiskLevel, pr.post_id
								FROM (
									SELECT hf.fk_id, MIN(hf.risk_level) AS risk_level
									FROM drh_post_result_hazar_factors hf
									GROUP BY hf.fk_id
								) hft
									LEFT JOIN drh_post_result pr ON pr.id = hft.fk_id
								WHERE pr.post_id IS NOT NULL
								GROUP BY pr.post_id
							) a
							ON a.post_id = rup.post_id
							LEFT JOIN drh_risk_unit ru ON ru.id = rup.risk_unit_id
						WHERE ru.unit_source = '1'
					) ht1
					UNION ALL
					SELECT ht2.*
					FROM (
						SELECT a.*, rup.risk_unit_id
						FROM drh_risk_unit_post rup
							LEFT JOIN (
								SELECT MIN(hft.risk_level) AS postRiskLevel, sm.post_id
								FROM (
									SELECT hf.fk_id, MIN(hf.risk_level) AS risk_level
									FROM drh_post_result_hazar_factors hf
									GROUP BY hf.fk_id
								) hft
									LEFT JOIN drh_safety_matters sm ON sm.id = hft.fk_id
								WHERE sm.post_id IS NOT NULL
								GROUP BY sm.post_id
							) a
							ON a.post_id = rup.post_id
							LEFT JOIN drh_risk_unit ru ON ru.id = rup.risk_unit_id
						WHERE ru.unit_source = '2'
					) ht2
				) ull
				GROUP BY ull.risk_unit_id
			) tll
				LEFT JOIN sys_dict_item dt ON tll.unitRiskLevel = dt.item_value
				LEFT JOIN sys_dict d ON dt.dict_id = d.id
			WHERE d.dict_code = 'drh_inherent_risk_level'
		) c
		ON c.risk_unit_id = rup.risk_unit_id
) g
WHERE g.postRiskLevelText IS NOT NULL
	AND g.entid = 1
	AND g.baseid = 1
ORDER BY g.create_time DESC
LIMIT 10;


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在这里插入图片描述

耗时22秒 接下来我们分析下
我们通过分析得出 这里面的tablederived2 的rows是一个笛卡尔积 他的数量等于id=2的所有操作 ，其实通过sql可以看出这里不难得出子查套子查询 导致查询效率低
在这里插入图片描述
一个主表 left 两个子查询后 外面又套了一个子查询
意思是 子查询 套子查询 导致查询结果比较慢，那么我们就这样优化 如下

SELECT DISTINCT ru.id AS unitId, ru.unit_name AS unitName, ru.create_time, ru.baseid, ru.entid
		, p.id AS postId, p.post_name AS postName, IFNULL(a.patrolNum, 0) AS patrolNum
		, IFNULL(ht.hiddenNum, 0) AS hiddenNum, b.postRiskLevel
		, b.postRiskLevelText, c.unitRiskLevel, c.unitRiskLevelText
	FROM drh_risk_unit_post rup
		LEFT JOIN drh_risk_unit ru ON ru.id = rup.risk_unit_id
		LEFT JOIN ent_post p ON p.id = rup.post_id
		LEFT JOIN (
			SELECT COUNT(1) AS patrolNum, pp.post_id
			FROM drh_post_patrol pp
			GROUP BY pp.post_id
		) a
		ON a.post_id = rup.post_id
		LEFT JOIN (
			SELECT COUNT(1) AS hiddenNum, h.post_id
			FROM drh_hidden h
			GROUP BY h.post_id
		) ht
		ON ht.post_id = rup.post_id
		LEFT JOIN  
     (
SELECT llt.*, dt.item_text AS postRiskLevelText
			FROM (
				SELECT ht1.*
				FROM (
					SELECT a.*, rup.risk_unit_id
					FROM drh_risk_unit_post rup
						LEFT JOIN (
							SELECT MIN(hft.risk_level) AS postRiskLevel, pr.post_id
							FROM (
								SELECT hf.fk_id, MIN(hf.risk_level) AS risk_level
								FROM drh_post_result_hazar_factors hf
								GROUP BY hf.fk_id
							) hft
								LEFT JOIN drh_post_result pr ON pr.id = hft.fk_id
							WHERE pr.post_id IS NOT NULL
							GROUP BY pr.post_id
						) a
						ON a.post_id = rup.post_id
						LEFT JOIN drh_risk_unit ru ON ru.id = rup.risk_unit_id
					WHERE ru.unit_source = '1'
				) ht1
				UNION ALL
				SELECT ht2.*
				FROM (
					SELECT a.*, rup.risk_unit_id
					FROM drh_risk_unit_post rup
						LEFT JOIN (
							SELECT MIN(hft.risk_level) AS postRiskLevel, sm.post_id
							FROM (
								SELECT hf.fk_id, MIN(hf.risk_level) AS risk_level
								FROM drh_post_result_hazar_factors hf
								GROUP BY hf.fk_id
							) hft
								LEFT JOIN drh_safety_matters sm ON sm.id = hft.fk_id
							WHERE sm.post_id IS NOT NULL
							GROUP BY sm.post_id
						) a
						ON a.post_id = rup.post_id
						LEFT JOIN drh_risk_unit ru ON ru.id = rup.risk_unit_id
					WHERE ru.unit_source = '2'
				) ht2
			) llt
				LEFT JOIN sys_dict_item dt ON llt.postRiskLevel = dt.item_value
				LEFT JOIN sys_dict d ON dt.dict_id = d.id
			WHERE d.dict_code = 'drh_inherent_risk_level'
     )
    b
		ON b.risk_unit_id = rup.risk_unit_id
			AND b.post_id = rup.post_id
		LEFT JOIN (
       SELECT tll.*, dt.item_text AS unitRiskLevelText
			FROM (
				SELECT ull.risk_unit_id, MIN(ull.postRiskLevel) AS unitRiskLevel
				FROM (
					SELECT ht1.*
					FROM (
						SELECT a.*, rup.risk_unit_id
						FROM drh_risk_unit_post rup
							LEFT JOIN (
								SELECT MIN(hft.risk_level) AS postRiskLevel, pr.post_id
								FROM (
									SELECT hf.fk_id, MIN(hf.risk_level) AS risk_level
									FROM drh_post_result_hazar_factors hf
									GROUP BY hf.fk_id
								) hft
									LEFT JOIN drh_post_result pr ON pr.id = hft.fk_id
								WHERE pr.post_id IS NOT NULL
								GROUP BY pr.post_id
							) a
							ON a.post_id = rup.post_id
							LEFT JOIN drh_risk_unit ru ON ru.id = rup.risk_unit_id
						WHERE ru.unit_source = '1'
					) ht1
					UNION ALL
					SELECT ht2.*
					FROM (
						SELECT a.*, rup.risk_unit_id
						FROM drh_risk_unit_post rup
							LEFT JOIN (
								SELECT MIN(hft.risk_level) AS postRiskLevel, sm.post_id
								FROM (
									SELECT hf.fk_id, MIN(hf.risk_level) AS risk_level
									FROM drh_post_result_hazar_factors hf
									GROUP BY hf.fk_id
								) hft
									LEFT JOIN drh_safety_matters sm ON sm.id = hft.fk_id
								WHERE sm.post_id IS NOT NULL
								GROUP BY sm.post_id
							) a
							ON a.post_id = rup.post_id
							LEFT JOIN drh_risk_unit ru ON ru.id = rup.risk_unit_id
						WHERE ru.unit_source = '2'
					) ht2
				) ull
				GROUP BY ull.risk_unit_id
			) tll
				LEFT JOIN sys_dict_item dt ON tll.unitRiskLevel = dt.item_value
				LEFT JOIN sys_dict d ON dt.dict_id = d.id
			WHERE d.dict_code = 'drh_inherent_risk_level'
     ) 
    c
		ON c.risk_unit_id = rup.risk_unit_id
    WHERE 
    b.postRiskLevelText IS NOT NULL
    and ru.entid = 1
    and ru.baseid = 1
    ORDER BY ru.create_time DESC
    LIMIT 10

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我们这里验证一下是否是这样
通过验证我们发现1.多秒就执行完了 原先需要20秒
在这里插入图片描述

早cpu高峰的时候
1 通过top命令找到那台机器连接我们的mysql比较耗CPU
2 通过 top -H -p PID 找到我们mysql那个物理进程比较耗费cpu
然后根据sql找到当时执行的sql或者是
找到我们的后台程序对应的数据库监控工具进行查询哪些比较慢
我的web后台使用到了druid 通过druid监控也可以查询到一些慢查询的sql

参考：https://www.isolves.com/it/sjk/MYSQL/2022-03-11/51075.html
http://www.muzhuangnet.com/show/44458.html
http://t.zoukankan.com/wyy123-p-9258513.html
https://blog.csdn.net/asd051377305/article/details/113979657

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