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按照非索引列更新
在可重复读的事务隔离级别下，在非索引列上进行更新和删除会对所有数据行进行加锁，阻止其他会话对边进行任何数据的增删改操作。 如果更新或删除条件为c3=4且c3列上没有索引则： 1、不允许其他会话插入任意记录，因为所有记录的主键索引上存在X排他锁，无法申请插入意向X锁（lock_mode X insert intention waiting Record lock） 2、不允许其他会话删除任意记录，因为所有记录的主键索引上存在X排他锁 3、不允许其他会话更新任意记录。因为所有记录的主键索引上存在X排他锁
##=========================================## 测试数据： CREATE TABLE `tb4001` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `c1` int(11) DEFAULT NULL, `c2` varchar(200) DEFAULT NULL, `c3` int(11) DEFAULT NULL, PRIMARY KEY (`id`), KEY `idx_c1` (`c1`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8; insert into tb4001(c1,c2,c3) values(2,2,2); insert into tb4001(c1,c2,c3) values(4,4,4); insert into tb4001(c1,c2,c3) values(7,7,7); insert into tb4001(c1,c2,c3) values(8,8,8); ##=========================================## ##测试1：在没有索引的列上更新 ##事务隔离级别：RR 会话1： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=777 where c3=7; ##=========================================## 会话2: SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; insert into tb4001(c1,c2,c3) values(9,9,9); ##执行结果：会话2被阻塞 使用SHOW ENGINE INNODB STATUS G查看阻塞发生时的锁信息 ------- TRX HAS BEEN WAITING 13 SEC FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 75 page no 3 n bits 80 index PRIMARY of table `test1`.`tb4001` trx id 10573 lock_mode X insert intention waiting Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0 0: len 8; hex 73757072656d756d; asc supremum;; ------------------ ---TRANSACTION 10571, ACTIVE 404 sec 2 lock struct(s), heap size 1136, 5 row lock(s), undo log entries 1 MySQL thread id 52, OS thread handle 140674621650688, query id 1201 127.0.0.1 admin ##=========================================## 会话2: SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=888 where c3=8; ##执行结果：会话2被阻塞 使用SHOW ENGINE INNODB STATUS G查看阻塞发生时的锁信息 ------- TRX HAS BEEN WAITING 5 SEC FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 75 page no 3 n bits 80 index PRIMARY of table `test1`.`tb4001` trx id 10573 lock_mode X waiting Record lock, heap no 2 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 8; hex 8000000000000001; asc ;; 1: len 6; hex 00000000293c; asc )<;; 2: len 7; hex b90000001c0110; asc ;; 3: len 4; hex 80000002; asc ;; 4: len 1; hex 32; asc 2;; 5: len 4; hex 80000002; asc ;; ------------------ ---TRANSACTION 10571, ACTIVE 681 sec 2 lock struct(s), heap size 1136, 5 row lock(s), undo log entries 1 MySQL thread id 52, OS thread handle 140674621650688, query id 1201 127.0.0.1 admin ##=========================================## 会话2: SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; delete from tb4001 where c3=8; ##执行结果：会话2被阻塞 使用SHOW ENGINE INNODB STATUS G查看阻塞发生时的锁信息 ------- TRX HAS BEEN WAITING 4 SEC FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 75 page no 3 n bits 80 index PRIMARY of table `test1`.`tb4001` trx id 10573 lock_mode X waiting Record lock, heap no 2 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 8; hex 8000000000000001; asc ;; 1: len 6; hex 00000000293c; asc )<;; 2: len 7; hex b90000001c0110; asc ;; 3: len 4; hex 80000002; asc ;; 4: len 1; hex 32; asc 2;; 5: len 4; hex 80000002; asc ;; ------------------ ---TRANSACTION 10571, ACTIVE 790 sec 2 lock struct(s), heap size 1136, 5 row lock(s), undo log entries 1 MySQL thread id 52, OS thread handle 140674621650688, query id 1201 127.0.0.1 admin
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按照非唯一索引更新
在可重复读的事务隔离级别下，按照非主键非唯一索引进行更新和删除，会对满足条件的行加行锁+满足条件的区域加gap锁 如果更新或删除条件为c1=4且c1列上有非唯一索引则： 1、允许其他会话插入c1<>4的记录，但不允许插入c1=4的记录 2、允许其他会话更新c1<>4的记录，但不允许将记录更新为c1=4的记录 3、允许其他会话删除c1<>4的记录。 4、允许插入删除修改在c1列索引上与c1=4相邻的记录，虽然操作会影响gap锁的边界值。
##=========================================## 测试数据： CREATE TABLE `tb4001` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `c1` int(11) DEFAULT NULL, `c2` varchar(200) DEFAULT NULL, `c3` int(11) DEFAULT NULL, PRIMARY KEY (`id`), KEY `idx_c1` (`c1`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8; insert into tb4001(c1,c2,c3) values(2,2,2); insert into tb4001(c1,c2,c3) values(4,4,4); insert into tb4001(c1,c2,c3) values(7,7,7); insert into tb4001(c1,c2,c3) values(8,8,8); ##=========================================## ##测试1：在没有索引的列上更新 ##事务隔离级别：RR 会话1： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=777 where c1=7; ##=========================================## 会话2: begin; SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; insert into tb4001(c1,c2,c3) values(9,9,9); 会话2未被阻塞成功执行 ##=========================================## 会话2: SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; insert into tb4001(c1,c2,c3) values(7,7,7); ##执行结果：会话2被阻塞 使用SHOW ENGINE INNODB STATUS G查看阻塞发生时的锁信息 ---TRANSACTION 10600, ACTIVE 7 sec inserting mysql tables in use 1, locked 1 LOCK WAIT 2 lock struct(s), heap size 1136, 1 row lock(s), undo log entries 1 MySQL thread id 53, OS thread handle 140674620851968, query id 1317 127.0.0.1 admin update insert into tb4001(c1,c2,c3) values(7,7,7) ------- TRX HAS BEEN WAITING 7 SEC FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 75 page no 4 n bits 72 index idx_c1 of table `test1`.`tb4001` trx id 10600 lock_mode X locks gap before rec insert intention waiting Record lock, heap no 5 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 80000008; asc ;; 1: len 8; hex 8000000000000004; asc ;; ------------------ ---TRANSACTION 10598, ACTIVE 270 sec 4 lock struct(s), heap size 1136, 3 row lock(s), undo log entries 1 MySQL thread id 52, OS thread handle 140674621650688, query id 1306 127.0.0.1 admin ##=========================================## 会话2: SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; delete from tb4001 where c1=8; 会话2未被阻塞成功执行 ##=========================================## 会话2: SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=888 where c1=8; 会话2未被阻塞成功执行 ##=========================================## 会话2: SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; delete from tb4001 where c1=4; 会话2未被阻塞成功执行 ##=========================================##
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按照非唯一索引+条件更新
在可重复读事务隔离级别下，按照对非唯一索引列进行更新，会对扫描到的所有索引记录进行更新，无论该记录是否满足WHERE中的其他条件。
##=========================================## 测试数据： CREATE TABLE `tb4001` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `c1` int(11) DEFAULT NULL, `c2` varchar(200) DEFAULT NULL, `c3` int(11) DEFAULT NULL, PRIMARY KEY (`id`), KEY `idx_c1` (`c1`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8; insert into tb4001(c1,c2,c3) values(2,2,2); insert into tb4001(c1,c2,c3) values(4,4,4); insert into tb4001(c1,c2,c3) values(4,4,44); insert into tb4001(c1,c2,c3) values(7,7,7); insert into tb4001(c1,c2,c3) values(8,8,8); ##=========================================## ##会话1： ##事务隔离级别：RR 会话1： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=444 where c1=4 and c3=4; ##=========================================## ##会话2： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=444 where c1=4 and c3=44; 会话2未被阻塞成功执行 ##执行结果：会话2被阻塞 mysql tables in use 1, locked 1 LOCK WAIT 2 lock struct(s), heap size 1136, 1 row lock(s) MySQL thread id 76, OS thread handle 140674621384448, query id 1636 127.0.0.1 admin updating update tb4001 set c2=444 where c1=4 and c3=44 ------- TRX HAS BEEN WAITING 13 SEC FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 79 page no 4 n bits 72 index idx_c1 of table `test1`.`tb4001` trx id 10781 lock_mode X waiting Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 80000004; asc ;; 1: len 8; hex 8000000000000002; asc ;; ------------------ ---TRANSACTION 10780, ACTIVE 52 sec 4 lock struct(s), heap size 1136, 5 row lock(s), undo log entries 1 MySQL thread id 75, OS thread handle 140674621916928, query id 1618 127.0.0.1 admin ##=========================================##
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按照非唯一组合索引更新
假设表TB1上有列C1和C2，有索引IDC_C1_C2(C1,C2) 在可重复提交事务隔离级别下,会话1按照C1=3 AND C2=4进行更新，则： 1、会话2按照C1=3 AND C2=4进行更新,更新操作被阻塞 2、会话2按照C1=3 AND C2=M(M<>4)进行更新,更新操作不会被阻塞 3、会话2可以在C1=3 AND C2=4之后间隙插入记录，但不能在C1=3 AND C2=4之前的间隙插入记录
##=========================================## ##测试数据 CREATE TABLE `tb4001` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `c1` int(11) DEFAULT NULL, `c2` varchar(200) DEFAULT NULL, `c3` int(11) DEFAULT NULL, PRIMARY KEY (`id`), KEY `idx_c1_c3` (`c1`,`c3`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8; insert into tb4001(c1,c2,c3) values(2,2,2); insert into tb4001(c1,c2,c3) values(4,4,4); insert into tb4001(c1,c2,c3) values(4,4,44); insert into tb4001(c1,c2,c3) values(7,7,7); insert into tb4001(c1,c2,c3) values(8,8,8); ##=========================================## ##会话1： ##事务隔离级别：RR 会话1： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=444 where c1=4 and c3=4; ##=========================================## ##会话2： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=444 where c1=4 and c3=44; 会话2未被阻塞成功执行 ##=========================================## ##会话2： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=444 where c1=2 and c3=2; 会话2未被阻塞成功执行 ##=========================================## ##会话2： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; insert into tb4001(c1,c2,c3) values(4,4,3); 会话2被阻塞 ##=========================================##
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按照唯一索引进行更新
在可重复读的事务隔离级别下，在唯一索引列上进行更新和删除在唯一索引的索引行上加排他锁。 如果更新或删除条件为c1=7且c1列上存在唯一索引则： 1、阻止其他会话删除和修改c1=7的记录 2、阻止其他会话插入c1=7的记录 3、允许其他会话插入删除修改c1<>7的记录，但不允许将记录修改为c1=7的记录 以上限制通过在唯一索引的索引记录上加排他锁X来实现，不会生产GAP锁 在根据唯一索引进行更新时，读提交事务隔离级别(RC)和可重复读事务隔离级别(RR)都只需要依赖唯一索引便可以保证事务ACID特性，无须使用GAP锁。
##=========================================## 测试数据： CREATE TABLE `tb4001` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `c1` int(11) DEFAULT NULL, `c2` varchar(200) DEFAULT NULL, `c3` int(11) DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `idx_c1` (`c1`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8; insert into tb4001(c1,c2,c3) values(2,2,2); insert into tb4001(c1,c2,c3) values(4,4,4); insert into tb4001(c1,c2,c3) values(7,7,7); insert into tb4001(c1,c2,c3) values(8,8,8); ##=========================================## ##测试1：在没有索引的列上更新 ##事务隔离级别：RR 会话1： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=777 where c1=7; ##=========================================## 会话2： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; insert into tb4001(c1,c2,c3) values(6,6,6); 会话2未被阻塞成功执行 ##=========================================## 会话2： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; insert into tb4001(c1,c2,c3) values(7,7,7); ##执行结果：会话2被阻塞 使用SHOW ENGINE INNODB STATUS G查看阻塞发生时的锁信息 ---TRANSACTION 10727, ACTIVE 9 sec inserting mysql tables in use 1, locked 1 LOCK WAIT 2 lock struct(s), heap size 1136, 1 row lock(s), undo log entries 1 MySQL thread id 53, OS thread handle 140674620851968, query id 1553 127.0.0.1 admin update insert into tb4001(c1,c2,c3) values(7,7,7) ------- TRX HAS BEEN WAITING 9 SEC FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 77 page no 4 n bits 72 index idx_c1 of table `test1`.`tb4001` trx id 10727 lock mode S waiting Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 80000007; asc ;; 1: len 8; hex 8000000000000003; asc ;; ------------------ ---TRANSACTION 10721, ACTIVE 32 sec 3 lock struct(s), heap size 1136, 2 row lock(s), undo log entries 1 MySQL thread id 52, OS thread handle 140674621650688, query id 1544 127.0.0.1 admin ##=========================================## 会话2： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c2=888 where c1=8; 会话2未被阻塞成功执行 ##=========================================## 会话2： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; update tb4001 set c1=7 where c1=8; 会话2未被阻塞成功执行 ##执行结果：会话2被阻塞 使用SHOW ENGINE INNODB STATUS G查看阻塞发生时的锁信息 ---TRANSACTION 10730, ACTIVE 4 sec updating or deleting mysql tables in use 1, locked 1 LOCK WAIT 4 lock struct(s), heap size 1136, 3 row lock(s), undo log entries 1 MySQL thread id 53, OS thread handle 140674620851968, query id 1567 127.0.0.1 admin updating update tb4001 set c1=7 where c1=8 ------- TRX HAS BEEN WAITING 4 SEC FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 77 page no 4 n bits 72 index idx_c1 of table `test1`.`tb4001` trx id 10730 lock mode S waiting Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 80000007; asc ;; 1: len 8; hex 8000000000000003; asc ;; ------------------ ---TRANSACTION 10721, ACTIVE 100 sec 3 lock struct(s), heap size 1136, 2 row lock(s), undo log entries 1 MySQL thread id 52, OS thread handle 140674621650688, query id 1544 127.0.0.1 admin ##=========================================## 会话2： SET SESSION tx_isolation='REPEATABLE-READ'; START TRANSACTION; SELECT @@GLOBAL.tx_isolation, @@SESSION.tx_isolation; delete from tb4001 where c1=8; 会话2未被阻塞成功执行
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