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MySQL锁阻塞分析
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日常維護中，經常會碰到線程被阻塞，導致數據庫響應非常慢，下面就看看如何獲取是哪個線程導致了阻塞的。
blog地址：http://blog.csdn.net/hw_libo/article/details/39080809
1. 環境說明
RHEL 6.4 x86_64 + MySQL 5.6.19
事務隔離級別：RR
2. 測試過程
3. 查看鎖阻塞線程信息
這里用幾中方法進行分析：
3.1 ?使用show processlist查看
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MySQL?[(none)]>?show?processlist;?? +?? |?Id?|?User?|?Host??????|?db???|?Command?|?Time?|?State????????|?Info?????????????????????????????????????|?? +?? |??2?|?root?|?localhost?|?NULL?|?Query???|????0?|?init?????????|?show?processlist?????????????????????????|?? |??3?|?root?|?localhost?|?test?|?Query???|???70?|?Sending?data?|?select?count(*)?from?t3?a,t3?b???????????|?? |??4?|?root?|?localhost?|?test?|?Query???|???65?|?updating?????|?delete?from?emp?where?empno=7788?????????|?? |??7?|?root?|?localhost?|?test?|?Query???|???68?|?updating?????|?update?emp?set?sal=3500?where?empno=7788?|?? +?? 4?rows?in?set?(0.00?sec)??
如果數據庫存在較多線程的話，這種方法確實不太好確認的。
3.2 ?直接使用show engine innodb status查看
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------------?? TRANSACTIONS?? ------------?? Trx?id?counter?4131?? Purge?done?for?trx's?n:o?<?4119?undo?n:o?<?0?state:?running?but?idle?? History?list?length?126?? LIST?OF?TRANSACTIONS?FOR?EACH?SESSION:?? ---TRANSACTION?0,?not?started?? MySQL?thread?id?2,?OS?thread?handle?0x7f953ffff700,?query?id?115?localhost?root?init?? show?engine?innodb?status?? ---TRANSACTION?4130,?ACTIVE?41?sec?starting?index?read?? mysql?tables?in?use?1,?locked?1?? LOCK?WAIT?2?lock?struct(s),?heap?size?360,?1?row?lock(s)?? MySQL?thread?id?4,?OS?thread?handle?0x7f953ff9d700,?query?id?112?localhost?root?updating?? delete?from?emp?where?empno=7788?? -------?TRX?HAS?BEEN?WAITING?41?SEC?FOR?THIS?LOCK?TO?BE?GRANTED:???##?等待了41s?? RECORD?LOCKS?space?id?16?page?no?3?n?bits?88?index?`PRIMARY`?of?table?`test`.`emp`?trx?id?4130?lock_mode?X?locks?rec?but?not?gap?waiting?? Record?lock,?heap?no?9?PHYSICAL?RECORD:?n_fields?10;?compact?format;?info?bits?0??##?線程4在等待往test.emp中的主鍵上加X鎖，page?num=3?? ?0:?len?4;?hex?80001e6c;?asc????l;;?? ?1:?len?6;?hex?000000001018;?asc???????;;?? ?2:?len?7;?hex?91000001420084;?asc?????B??;;?? ?3:?len?5;?hex?53434f5454;?asc?SCOTT;;?? ?4:?len?7;?hex?414e414c595354;?asc?ANALYST;;?? ?5:?len?4;?hex?80001d8e;?asc?????;;?? ?6:?len?4;?hex?208794f0;?asc?????;;?? ?7:?len?4;?hex?80000bb8;?asc?????;;?? ?8:?SQL?NULL;?? ?9:?len?4;?hex?80000014;?asc?????;;?? ?? ------------------?? ---TRANSACTION?4129,?ACTIVE?45?sec?starting?index?read?? mysql?tables?in?use?1,?locked?1?? LOCK?WAIT?2?lock?struct(s),?heap?size?360,?1?row?lock(s)?? MySQL?thread?id?7,?OS?thread?handle?0x7f953ff6c700,?query?id?111?localhost?root?updating?? update?emp?set?sal=3500?where?empno=7788?? -------?TRX?HAS?BEEN?WAITING?45?SEC?FOR?THIS?LOCK?TO?BE?GRANTED:???##?等待了45s?? RECORD?LOCKS?space?id?16?page?no?3?n?bits?88?index?`PRIMARY`?of?table?`test`.`emp`?trx?id?4129?lock_mode?X?locks?rec?but?not?gap?waiting?? Record?lock,?heap?no?9?PHYSICAL?RECORD:?n_fields?10;?compact?format;?info?bits?0??##?線程7在等待往test.emp中的主鍵上加X鎖，page?num=3?? ?0:?len?4;?hex?80001e6c;?asc????l;;?? ?1:?len?6;?hex?000000001018;?asc???????;;?? ?2:?len?7;?hex?91000001420084;?asc?????B??;;?? ?3:?len?5;?hex?53434f5454;?asc?SCOTT;;?? ?4:?len?7;?hex?414e414c595354;?asc?ANALYST;;?? ?5:?len?4;?hex?80001d8e;?asc?????;;?? ?6:?len?4;?hex?208794f0;?asc?????;;?? ?7:?len?4;?hex?80000bb8;?asc?????;;?? ?8:?SQL?NULL;?? ?9:?len?4;?hex?80000014;?asc?????;;?? ?? ------------------?? ---TRANSACTION?4128,?ACTIVE?51?sec?? 2?lock?struct(s),?heap?size?360,?1?row?lock(s)?? MySQL?thread?id?3,?OS?thread?handle?0x7f953ffce700,?query?id?110?localhost?root?cleaning?up??
我們知道，主要根因還是thread=3引起的，但從innodb status中卻無法分析得到這個結果。
從上面來看，線程4和線程7都在等待往test.emp中的主鍵上加X鎖，page num=3，但是線程7等待的時間為45s，而線程4等待的時間為41s，是較線程7之后申請的鎖，所以可以判斷是線程7阻塞了線程4。至于線程7為什么出現等待，這里分析不到根因。
3.3 ?使用mysqladmin debug查看
# mysqladmin -S /tmp/mysql3306.sock debug
然后在error日志中，會看到：
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Thread?database.table_name??????????Locked/Waiting????????Lock_type?? ?? ?? 3???????test.t3?????????????????????Locked?-?read?????????Low?priority?read?lock?? 7???????test.emp????????????????????Locked?-?write????????High?priority?write?lock??
這種方法中，能找到線程ID=3和7是阻塞者，但還是不太準確，判斷不出來線程7也是被線程ID=3阻塞的。
3.4 ?使用innodb_lock_monitor來獲取阻塞鎖線程
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MySQL?[test]>?CREATE?TABLE?innodb_lock_monitor?(a?INT)?ENGINE=INNODB;??##?隨便在一個數據庫中創建這個表，就會打開lock?monitor?? Query?OK,?0?rows?affected,?1?warning?(0.07?sec)?? ?? MySQL?[test]>?show?warnings\G?? ***************************?1.?row?***************************?? ??Level:?Warning?? ???Code:?131?? Message:?Using?the?table?name?innodb_lock_monitor?to?enable?diagnostic?output?is?deprecated?and?may?be?removed?in?future?releases.?Use?INFORMATION_SCHEMA?or?PERFORMANCE_SCHEMA?tables?or?SET?GLOBAL?innodb_status_output=ON.?? 1?row?in?set?(0.00?sec)??
說明：這個在5.6中有一個warning，但不影響使用。
然后再使用show engine innodb status查看：
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------------?? TRANSACTIONS?? ------------?? Trx?id?counter?4667?? Purge?done?for?trx's?n:o?<?4659?undo?n:o?<?0?state:?running?but?idle?? History?list?length?138?? LIST?OF?TRANSACTIONS?FOR?EACH?SESSION:?? ---TRANSACTION?0,?not?started?? MySQL?thread?id?9,?OS?thread?handle?0x7f813c5f7700,?query?id?152?localhost?root?init?? show?engine?innodb?status?? ---TRANSACTION?4663,?ACTIVE?78?sec?starting?index?read?? mysql?tables?in?use?1,?locked?1?? LOCK?WAIT?2?lock?struct(s),?heap?size?360,?1?row?lock(s)?? MySQL?thread?id?4,?OS?thread?handle?0x7f813c628700,?query?id?149?localhost?root?updating?? delete?from?emp?where?empno=7788?? -------?TRX?HAS?BEEN?WAITING?78?SEC?FOR?THIS?LOCK?TO?BE?GRANTED:???##?等待了78s?? RECORD?LOCKS?space?id?16?page?no?3?n?bits?88?index?`PRIMARY`?of?table?`test`.`emp`?trx?id?4663?lock_mode?X?locks?rec?but?not?gap?waiting?? Record?lock,?heap?no?9?PHYSICAL?RECORD:?n_fields?10;?compact?format;?info?bits?0??##?線程4在等待往test.emp中的主鍵上加X鎖，page?num=3?? ?0:?len?4;?hex?80001e6c;?asc????l;;?? ?1:?len?6;?hex?000000001018;?asc???????;;?? ?2:?len?7;?hex?91000001420084;?asc?????B??;;?? ?3:?len?5;?hex?53434f5454;?asc?SCOTT;;?? ?4:?len?7;?hex?414e414c595354;?asc?ANALYST;;?? ?5:?len?4;?hex?80001d8e;?asc?????;;?? ?6:?len?4;?hex?208794f0;?asc?????;;?? ?7:?len?4;?hex?80000bb8;?asc?????;;?? ?8:?SQL?NULL;?? ?9:?len?4;?hex?80000014;?asc?????;;?? ?? ------------------?? TABLE?LOCK?table?`test`.`emp`?trx?id?4663?lock?mode?IX???##?在給主鍵行上加X鎖之前，先要在表上加意向鎖IX?? RECORD?LOCKS?space?id?16?page?no?3?n?bits?88?index?`PRIMARY`?of?table?`test`.`emp`?trx?id?4663?lock_mode?X?locks?rec?but?not?gap?waiting?? Record?lock,?heap?no?9?PHYSICAL?RECORD:?n_fields?10;?compact?format;?info?bits?0?? ?0:?len?4;?hex?80001e6c;?asc????l;;?? ?1:?len?6;?hex?000000001018;?asc???????;;?? ?2:?len?7;?hex?91000001420084;?asc?????B??;;?? ?3:?len?5;?hex?53434f5454;?asc?SCOTT;;?? ?4:?len?7;?hex?414e414c595354;?asc?ANALYST;;?? ?5:?len?4;?hex?80001d8e;?asc?????;;?? ?6:?len?4;?hex?208794f0;?asc?????;;?? ?7:?len?4;?hex?80000bb8;?asc?????;;?? ?8:?SQL?NULL;?? ?9:?len?4;?hex?80000014;?asc?????;;?? ?? ---TRANSACTION?4662,?ACTIVE?81?sec?starting?index?read?? mysql?tables?in?use?1,?locked?1?? LOCK?WAIT?2?lock?struct(s),?heap?size?360,?1?row?lock(s)?? MySQL?thread?id?7,?OS?thread?handle?0x7f813c5c6700,?query?id?148?localhost?root?updating?? update?emp?set?sal=3500?where?empno=7788?? -------?TRX?HAS?BEEN?WAITING?81?SEC?FOR?THIS?LOCK?TO?BE?GRANTED:??##?等待了81s?? RECORD?LOCKS?space?id?16?page?no?3?n?bits?88?index?`PRIMARY`?of?table?`test`.`emp`?trx?id?4662?lock_mode?X?locks?rec?but?not?gap?waiting?? Record?lock,?heap?no?9?PHYSICAL?RECORD:?n_fields?10;?compact?format;?info?bits?0??##?線程7在等待往test.emp中的主鍵上加X鎖，page?num=3?? ?0:?len?4;?hex?80001e6c;?asc????l;;?? ?1:?len?6;?hex?000000001018;?asc???????;;?? ?2:?len?7;?hex?91000001420084;?asc?????B??;;?? ?3:?len?5;?hex?53434f5454;?asc?SCOTT;;?? ?4:?len?7;?hex?414e414c595354;?asc?ANALYST;;?? ?5:?len?4;?hex?80001d8e;?asc?????;;?? ?6:?len?4;?hex?208794f0;?asc?????;;?? ?7:?len?4;?hex?80000bb8;?asc?????;;?? ?8:?SQL?NULL;?? ?9:?len?4;?hex?80000014;?asc?????;;?? ?? ------------------?? TABLE?LOCK?table?`test`.`emp`?trx?id?4662?lock?mode?IX???##?在給主鍵行上加X鎖之前，先要在表上加意向鎖IX?? RECORD?LOCKS?space?id?16?page?no?3?n?bits?88?index?`PRIMARY`?of?table?`test`.`emp`?trx?id?4662?lock_mode?X?locks?rec?but?not?gap?waiting?? Record?lock,?heap?no?9?PHYSICAL?RECORD:?n_fields?10;?compact?format;?info?bits?0?? ?0:?len?4;?hex?80001e6c;?asc????l;;?? ?1:?len?6;?hex?000000001018;?asc???????;;?? ?2:?len?7;?hex?91000001420084;?asc?????B??;;?? ?3:?len?5;?hex?53434f5454;?asc?SCOTT;;?? ?4:?len?7;?hex?414e414c595354;?asc?ANALYST;;?? ?5:?len?4;?hex?80001d8e;?asc?????;;?? ?6:?len?4;?hex?208794f0;?asc?????;;?? ?7:?len?4;?hex?80000bb8;?asc?????;;?? ?8:?SQL?NULL;?? ?9:?len?4;?hex?80000014;?asc?????;;?? ?? ---TRANSACTION?4615,?ACTIVE?1579?sec,?thread?declared?inside?InnoDB?1222?? mysql?tables?in?use?2,?locked?0?? 2?lock?struct(s),?heap?size?360,?1?row?lock(s)?? MySQL?thread?id?3,?OS?thread?handle?0x7f813c659700,?query?id?147?localhost?root?Sending?data?? select?count(*)?from?t3?a,t3?b???##?這是線程3當前正在執行的SQL?? Trx?read?view?will?not?see?trx?with?id?>=?4662,?sees?<?4659?? TABLE?LOCK?table?`test`.`emp`?trx?id?4615?lock?mode?IX??##?線程3中正在擁有表上的意向IX鎖，并且有test.emp表上主鍵的行級X鎖，page?num=3?? RECORD?LOCKS?space?id?16?page?no?3?n?bits?88?index?`PRIMARY`?of?table?`test`.`emp`?trx?id?4615?lock_mode?X?locks?rec?but?not?gap?? Record?lock,?heap?no?9?PHYSICAL?RECORD:?n_fields?10;?compact?format;?info?bits?0?? ?0:?len?4;?hex?80001e6c;?asc????l;;?? ?1:?len?6;?hex?000000001018;?asc???????;;?? ?2:?len?7;?hex?91000001420084;?asc?????B??;;?? ?3:?len?5;?hex?53434f5454;?asc?SCOTT;;?? ?4:?len?7;?hex?414e414c595354;?asc?ANALYST;;?? ?5:?len?4;?hex?80001d8e;?asc?????;;?? ?6:?len?4;?hex?208794f0;?asc?????;;?? ?7:?len?4;?hex?80000bb8;?asc?????;;?? ?8:?SQL?NULL;?? ?9:?len?4;?hex?80000014;?asc?????;;??
為什么線程3當前執行的是一個select t3表操作，但卻鎖住了test.emp表上page num=3？
有可能是線程3之前對test.emp表的操作事務沒有及時提交導致。
所以得出：線程3阻塞了線程7，而線程7又阻塞了線程4，所以根因就是線程3，讓線程3盡快提交或是kill掉即可。
4. 結論
在分析innodb中鎖阻塞時，幾種方法的對比情況：
（1）使用show processlist查看不靠譜；
（2）直接使用show engine innodb status查看，無法判斷到問題的根因；
（3）使用mysqladmin debug查看，能看到所有產生鎖的線程，但無法判斷哪個才是根因；
（4）開啟innodb_lock_monitor后，再使用show engine innodb status查看，能夠找到鎖阻塞的根因。
blog地址：http://blog.csdn.net/hw_libo/article/details/39080809
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