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今天就跟大家聊聊有關MySQL數據庫中的鎖阻塞是什么，可能很多人都不太了解，為了讓大家更加了解，小編給大家總結了以下內容，希望大家根據這篇文章可以有所收獲。
1. 環境說明
RHEL 6.4 x86_64 + MySQL 5.6.19
事務隔離級別：RR
這里用幾中方法進行分析：
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。
------------ 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。
# mysqladmin -S /tmp/mysql3306.sock debug
然后在error日志中，會看到：
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。
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：
------------ 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。
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。
看完上述內容，你們對MySQL數據庫中的鎖阻塞是什么有進一步的了解嗎？如果還想了解更多知識或者相關內容，請關注億速云行業資訊頻道，感謝大家的支持。
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