文章目錄

• 生猛干貨
• 版本信息
• MySQL 行鎖分析
• MySQL死鎖演示
• 排查過(guò)程
• 查看近期死鎖日志信息
• 查詢鎖等待命令及kill 鎖
• 優(yōu)化建議
• 搞定MySQL

生猛干貨

帶你搞定MySQL實(shí)戰(zhàn)，輕松對(duì)應(yīng)海量業(yè)務(wù)處理及高并發(fā)需求，從容應(yīng)對(duì)大場(chǎng)面試

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版本信息

mysql> select version(); +-----------+ | version() | +-----------+ | 5.7.28 | +-----------+ 1 row in setmysql>

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MySQL 行鎖分析

mysql> show status like'innodb_row_lock%'; +-------------------------------+--------+ | Variable_name | Value | +-------------------------------+--------+ | Innodb_row_lock_current_waits | 0 | | Innodb_row_lock_time | 222821 | | Innodb_row_lock_time_avg | 27852 | | Innodb_row_lock_time_max | 51017 | | Innodb_row_lock_waits | 8 | +-------------------------------+--------+ 5 rows in setmysql>

變量說(shuō)明：

• Innodb_row_lock_current_waits 當(dāng)前正在等待鎖定的數(shù)量 單位毫秒
• Innodb_row_lock_time 從系統(tǒng)啟動(dòng)到現(xiàn)在鎖定總時(shí)間長(zhǎng)度 單位毫秒
• Innodb_row_lock_time_avg 每次等待所花平均時(shí)間 單位毫秒
• Innodb_row_lock_time_max 從系統(tǒng)啟動(dòng)到現(xiàn)在等待最長(zhǎng)的一次所花時(shí)間 單位毫秒
• Innodb_row_lock_waits 系統(tǒng)啟動(dòng)后到現(xiàn)在總共等待的次數(shù)

重點(diǎn)關(guān)注 ： Innodb_row_lock_time_avg 、Innodb_row_lock_waits 、Innodb_row_lock_time

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MySQL死鎖演示

事務(wù)隔離級(jí)別， 默認(rèn) 可重復(fù)讀

mysql> show variables like '%tx_isolation%'; +---------------+-----------------+ | Variable_name | Value | +---------------+-----------------+ | tx_isolation | REPEATABLE-READ | +---------------+-----------------+ 1 row in setmysql>

【操作步驟】

session1session2

begin 模擬開啟事務(wù)
select * from art_info where id=1 for update;
	begin 模擬開啟事務(wù)
	select * from account where id=2 for update;
select * from art_info where id=2 for update; ---->一直等待
	select * from art_info where id=1 for update; —> Deadlock found when trying to get lock; try restarting transaction

大多數(shù)情況mysql可以自動(dòng)檢測(cè)死鎖并回滾產(chǎn)生死鎖的那個(gè)事務(wù)，但是有些情況mysql沒(méi)法自動(dòng)檢測(cè)死鎖

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排查過(guò)程

【模擬鎖等待 】

session1session2

begin 模擬開啟事務(wù)
select * from art_info where id=1 for update;
	begin 模擬開啟事務(wù)
	select * from account where id=2 for update;
select * from account where id=2 for update;

mysql> select * from art_info where id =2 for update ; 1205 - Lock wait timeout exceeded; try restarting transaction

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-- 查看事務(wù) select * from information_schema.INNODB_TRX; -- 查看鎖 select * from information_schema.INNODB_LOCKS; -- 查看鎖等待 select * from information_schema.INNODB_LOCK_WAITS;-- 鎖釋放 information_schema.INNODB_TRX 查詢 trx_mysql_thread_id 然后去 kill 對(duì)應(yīng)的value kill trx_mysql_thread_id

來(lái)吧 ，用上面的SQL查吧

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查看近期死鎖日志信息

show engine innodb status \G;

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查詢鎖等待命令及kill 鎖

-- 查看事務(wù) select * from information_schema.INNODB_TRX; -- 查看鎖 select * from information_schema.INNODB_LOCKS; -- 查看鎖等待 select * from information_schema.INNODB_LOCK_WAITS;-- 鎖釋放 information_schema.INNODB_TRX 查詢 trx_mysql_thread_id 然后去 kill 對(duì)應(yīng)的value kill trx_mysql_thread_id

鎖等待有自己的超時(shí)時(shí)間，超過(guò)后一般都會(huì)自動(dòng)釋放

mysql> select * from art_info where id =2 for update ; 1205 - Lock wait timeout exceeded; try restarting transaction

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優(yōu)化建議

• 盡可能讓所有數(shù)據(jù)檢索都通過(guò)索引來(lái)完成，避免無(wú)索引行鎖升級(jí)為表鎖
• 合理設(shè)計(jì)索引，盡量縮小鎖的范圍
• 盡可能減少檢索條件范圍，避免間隙鎖
• 盡量控制事務(wù)大小，減少鎖定資源量和時(shí)間長(zhǎng)度，涉及事務(wù)加鎖的sql盡量放在事務(wù)最后執(zhí)行
• 盡可能低級(jí)別事務(wù)隔離

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搞定MySQL

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