MySQL 间隙锁

一.根据案例二：不同索引加锁顺序的问题，模拟重现死锁（详细操作步骤）

1.RR级别下，更新操作默认会加行级锁，行级锁会对索引加锁
2.如果更新语句使用多个索引，行级锁会先锁定普通索引，再锁定聚簇索引
3.如果两个SQL用到了不同的普通索引，或者一个用了，另外一个没用
4.会导致这两个SQL加行级锁的顺序不一致，形成多个事物之间X锁的循环等待，形成死锁

1.1表结构

root@slave01 22:28:  [sqltest]> create table user_info (id int primary key,username varchar(20), status tinyint,key(username));

Query OK, 0 rows affected (0.03 sec)

#

root@slave01 22:54:  [sqltest]> show create table user_info;

+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

| Table     | Create Table                                                                                                                                                                                                            |

+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

| user_info | CREATE TABLE `user_info` (

  `id` int(11) NOT NULL,

  `username` varchar(20) DEFAULT NULL,

  `status` tinyint(4) DEFAULT NULL,

  PRIMARY KEY (`id`),

  KEY `username` (`username`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8 |

+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

1 row in set (0.00 sec)

#

insert into user_info values(1,'yzw1',1);

insert into user_info values(3,'yzw3',0);

insert into user_info values(5,'yzw5',1);

1.2执行计划

root@master 23:15:  [sqltest]> desc update user_info set status=1 where username='yzw3';

+----+-------------+-----------+------------+-------+---------------+----------+---------+-------+------+----------+-------------+

| id | select_type | table     | partitions | type  | possible_keys | key      | key_len | ref   | rows | filtered | Extra       |

+----+-------------+-----------+------------+-------+---------------+----------+---------+-------+------+----------+-------------+

|  1 | UPDATE      | user_info | NULL       | range | username      | username | 63      | const |    1 |   100.00 | Using where |

+----+-------------+-----------+------------+-------+---------------+----------+---------+-------+------+----------+-------------+

1 row in set (0.01 sec)

#

root@master 23:15:  [sqltest]> desc update user_info set username='yzw33' where id=3;

+----+-------------+-----------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+

| id | select_type | table     | partitions | type  | possible_keys | key     | key_len | ref   | rows | filtered | Extra       |

+----+-------------+-----------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+

|  1 | UPDATE      | user_info | NULL       | range | PRIMARY       | PRIMARY | 4       | const |    1 |   100.00 | Using where |

+----+-------------+-----------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+

1 row in set (0.00 sec)

1.3重现

session 1	session 2
begin; update user_info set status=1 where username='yzw3';
此时session除了给索引username加x锁，还给主键索引id=3的行记录加了x锁，但是这两个锁并不是同时获取的
第一步先获取普通索引username上的X锁
此时session 2进行更新	begin; update user_info set username='yzw33' where id=3;
	session 2 第一步需要先获取聚簇索引，也就是主键索引上的X锁第二步需要获取普通索引username上的X锁
	出现死锁ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
需要session 2的主键索引X锁	需要session 1的普通索引username X锁

root@master 23:11:  [(none)]> select * from information_schema.innodb_locks;

+-------------------+-------------+-----------+-----------+-----------------------+------------+------------+-----------+----------+-----------+

| lock_id           | lock_trx_id | lock_mode | lock_type | lock_table            | lock_index | lock_space | lock_page | lock_rec | lock_data |

+-------------------+-------------+-----------+-----------+-----------------------+------------+------------+-----------+----------+-----------+

| 48736590:1135:3:3 | 48736590    | X         | RECORD    | `sqltest`.`user_info` | PRIMARY    |       1135 |         3 |        3 | 3         |

| 48733648:1135:3:3 | 48733648    | X         | RECORD    | `sqltest`.`user_info` | PRIMARY    |       1135 |         3 |        3 | 3         |

+-------------------+-------------+-----------+-----------+-----------------------+------------+------------+-----------+----------+-----------+

2 rows in set, 1 warning (0.00 sec)

1.4重现

1.给status列增加索引

create index idx_status on user_info(status);

2.执行计划，两条语句都是走的普通索引

root@master 23:26:  [sqltest]> desc update user_info set status=1 where username='yzw3';

+----+-------------+-----------+------------+-------+---------------+----------+---------+-------+------+----------+-------------+

| id | select_type | table     | partitions | type  | possible_keys | key      | key_len | ref   | rows | filtered | Extra       |

+----+-------------+-----------+------------+-------+---------------+----------+---------+-------+------+----------+-------------+

|  1 | UPDATE      | user_info | NULL       | range | username      | username | 63      | const |    1 |   100.00 | Using where |

+----+-------------+-----------+------------+-------+---------------+----------+---------+-------+------+----------+-------------+

1 row in set (0.04 sec)

#

root@master 23:29:  [sqltest]> desc update user_info set username='yzw33' where status=0;

+----+-------------+-----------+------------+-------+---------------+------------+---------+-------+------+----------+-------------+

| id | select_type | table     | partitions | type  | possible_keys | key        | key_len | ref   | rows | filtered | Extra       |

+----+-------------+-----------+------------+-------+---------------+------------+---------+-------+------+----------+-------------+

|  1 | UPDATE      | user_info | NULL       | range | idx_status    | idx_status | 2       | const |    1 |   100.00 | Using where |

+----+-------------+-----------+------------+-------+---------------+------------+---------+-------+------+----------+-------------+

1 row in set (0.01 sec)

3.两个会话更新索引

session 1	session 2
begin; update user_info set status=1 where username='yzw3';
第一步已经获取了username的普通索引X锁	begin; update user_info set username='yzw33' where status=0;
	第一步已经获取status的普通索引X锁第二步给主键索引加X锁
第二步需要给主键索引加X锁，无法获取	出现死锁ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
	因为要更新非主键索引username，因此要给username加X锁，但是无法获取

root@master 23:30:  [sqltest]> select * from information_schema.innodb_locks;

+-------------------+-------------+-----------+-----------+-----------------------+------------+------------+-----------+----------+-----------+

| lock_id           | lock_trx_id | lock_mode | lock_type | lock_table            | lock_index | lock_space | lock_page | lock_rec | lock_data |

+-------------------+-------------+-----------+-----------+-----------------------+------------+------------+-----------+----------+-----------+

| 48739611:1135:5:2 | 48739611    | X         | RECORD    | `sqltest`.`user_info` | idx_status |       1135 |         5 |        2 | 0, 3      |

| 48738737:1135:5:2 | 48738737    | X         | RECORD    | `sqltest`.`user_info` | idx_status |       1135 |         5 |        2 | 0, 3      |

+-------------------+-------------+-----------+-----------+-----------------------+------------+------------+-----------+----------+-----------+

2 rows in set, 1 warning (0.00 sec)

1.5多查询一次取主键，解决死锁

begin;

update user_info set status=1 where id in (select id  from (select id from user_info where username='yzw3') t);

begin;

update user_info set username='yzw33' where id in (select id from  (select id from user_info where status=0) t);

root@master 23:56:  [sqltest]> select * from information_schema.innodb_locks;

+-------------------+-------------+-----------+-----------+-----------------------+------------+------------+-----------+----------+-----------+

| lock_id           | lock_trx_id | lock_mode | lock_type | lock_table            | lock_index | lock_space | lock_page | lock_rec | lock_data |

+-------------------+-------------+-----------+-----------+-----------------------+------------+------------+-----------+----------+-----------+

| 48744368:1135:3:3 | 48744368    | X         | RECORD    | `sqltest`.`user_info` | PRIMARY    |       1135 |         3 |        3 | 3         |

| 48744353:1135:3:3 | 48744353    | X         | RECORD    | `sqltest`.`user_info` | PRIMARY    |       1135 |         3 |        3 | 3         |

+-------------------+-------------+-----------+-----------+-----------------------+------------+------------+-----------+----------+-----------+

2 rows in set, 1 warning (0.00 sec)

> 依然存在死锁，因为都给主键id加了X锁

二.根据方案三：TMS死锁分析和处理，模拟重现死锁（详细操作步骤）

1.构造数据

create table user_info1 (id int primary key,name varchar(10), level tinyint);

insert into user_info1 values(1,'AA',0);

insert into user_info1 values(3,'CC',0);

insert into user_info1 values(5,'EE',2);

insert into user_info1 values(7,'GG',5);

insert into user_info1 values(9,'GG',7);

insert into user_info1 values(11,'JJ',20);

session 1 >select * from user_info1;

+----+------+-------+

| id | name | level |

+----+------+-------+

|  1 | AA   |     0 |

|  3 | CC   |     0 |

|  5 | EE   |     2 |

|  7 | GG   |     5 |

|  9 | GG   |     7 |

| 11 | JJ   |    20 |

+----+------+-------+

6 rows in set (0.00 sec)

2.过程

session 1	session 2
	begin; insert into user_info1 values(2,'BB',1);
delete from user_info1 where name='BB'; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction	此时是RC级别 session 2首先插入数据并给这一行加X锁，因为没有索引，同时在两边加gap锁
delete from user_info1 where name='BC'; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
delete from user_info1 where level=8; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
delete where条件没有索引，会对整表扫描并加gap锁，但是此时session2已经加了gap锁，session1的delete事务被回退

delete from user_info1 where  name='BB'

------- TRX HAS BEEN WAITING 10 SEC FOR THIS LOCK TO BE GRANTED:

RECORD LOCKS space id 1137 page no 3 n bits 80 index PRIMARY of table `sqltest`.`user_info1` trx id 48906774 lock_mode X locks rec but not gap waiting

Record lock, heap no 8 PHYSICAL RECORD: n_fields 5; compact format; info bits 0

3保持RCset tx_isolation='READ-COMMITTED';级别，增加索引

session 1 >create index idx_name_level on user_info1(name,level);

Query OK, 0 rows affected (0.12 sec)

Records: 0  Duplicates: 0  Warnings: 0

session 1	session 2
	begin; insert into user_info1 values(2,'BB',1);
delete from user_info1 where name='BB'; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction	此时是RC级别 session 2首先插入数据并加gap锁，
session 1 >delete from user_info1 where name='BC'; Query OK, 0 rows affected (0.00 sec)	RC级别下，增加了索引，没有了gap锁
session 1 >delete from user_info1 where name='BB'; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction session 1 >delete from user_info1 where level=8; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction session 1 >delete from user_info1 where level=20; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction session 1 >delete from user_info1 where level=7; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction session 1 >delete from user_info1 where level=2; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction	索引(a,b)，如果where字段使用了索引a，则不存在gap锁了，猜测是单独使用索引b还是会存在gap锁，因为无法使用索引

root@master 16:31:  [(none)]> select * from information_schema.innodb_locks;

+-------------------+-------------+-----------+-----------+------------------------+------------+------------+-----------+----------+-----------+

| lock_id           | lock_trx_id | lock_mode | lock_type | lock_table             | lock_index | lock_space | lock_page | lock_rec | lock_data |

+-------------------+-------------+-----------+-----------+------------------------+------------+------------+-----------+----------+-----------+

| 48942672:1137:3:8 | 48942672    | X         | RECORD    | `sqltest`.`user_info1` | PRIMARY    |       1137 |         3 |        8 | 2         |

| 48942589:1137:3:8 | 48942589    | S         | RECORD    | `sqltest`.`user_info1` | PRIMARY    |       1137 |         3 |        8 | 2         |

+-------------------+-------------+-----------+-----------+------------------------+------------+------------+-----------+----------+-----------+

2 rows in set, 1 warning (0.00 sec)

4增加索引(b)，验证

session 1 >create index idx_level on user_info1(level);

Query OK, 0 rows affected (0.08 sec)

Records: 0  Duplicates: 0  Warnings: 0

session 1 | session 2

---|---

&nbsp; | begin;</br>insert into user_info1 values(2,'BB',1);

delete from user_info1 where  name='BB';</br>ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction | 此时是RC级别 session 2首先插入数据并加X锁

session 1 >delete from user_info1 where name='BC';</br>Query OK, 0 rows affected (0.00 sec)</br>session 1 >delete from user_info1 where name='BB';</br>ERROR 1205 (HY000): Lock wait timeout xceeded; try restarting transaction</br>session 1 >delete from user_info1 where level=8;</br>Query OK, 0 rows affected (0.01 sec)</br>session 1 >delete from user_info1 where level=20;</br>Query OK, 1 row affected (0.01 sec)</br>session 1 >delete from user_info1 where level=7;</br>Query OK, 1 row affected (0.00 sec)</br>session 1 >delete from user_info1 where level=2;</br>Query OK, 1 row affected (0.00 sec)</br>|此时b有了索引，RC级别下也就不存在gap锁了

5更改为RR级别set tx_isolation='REPEATABLE-READ';，先使用索引(a,b)

session 2 >drop index idx_level on user_info1;

Query OK, 0 rows affected (0.16 sec)

Records: 0  Duplicates: 0  Warnings: 0

session 2 >begin;

Query OK, 0 rows affected (0.00 sec)

#

session 2 >insert into user_info1 values(2,'BB',1);

Query OK, 1 row affected (0.00 sec)

#

session 1 >delete from user_info1 where name='BB';

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

session 1 >delete from user_info1 where name='BC';

Query OK, 0 rows affected (0.00 sec)

#

session 1 >delete from user_info1 where level=8;

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

session 1 >delete from user_info1 where level=2;

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

session 1 >delete from user_info1 where name='CB';

Query OK, 0 rows affected (0.00 sec)

#

session 1 >delete from user_info1 where name='BA';

Query OK, 0 rows affected (0.00 sec)

6总结

RC和RR级别下如果更新没有索引的字段，会加gap锁
必须能用上索引，(a,b)只用b是无效索引
RC增加了索引后就不存在gap锁了
RR级别在没有索引的情况，用不上索引也会产生gap锁
解决方法，最好使用RC级别+索引，或者RR下修改参数innodb_locks_unsafe_for_binlog=on
间隙锁只会block住insert操作

session 1 >select * from user_info1;

+----+------+-------+

| id | name | level |

+----+------+-------+

|  1 | AA   |     0 |

|  3 | BA   |     1 |

|  5 | EE   |     2 |

|  7 | GG   |     5 |

|  9 | GG   |     7 |

| 11 | JJ   |    20 |

+----+------+-------+

6 rows in set (0.00 sec)

#

session 1 >begin;

Query OK, 0 rows affected (0.00 sec)

#

session 1 >update user_info1 set level=3 where name='BA';

Query OK, 1 row affected (0.00 sec)

Rows matched: 1  Changed: 1  Warnings: 0

session 2 >begin;

Query OK, 0 rows affected (0.01 sec)

#

session 2 >insert into user_info1 values(2,'AB',1);

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

三.根据案例四：MySQL间隙锁导致的Deadlock分析，模拟重现死锁（详细操作步骤）

3.1 造数据

create table t3 (id int auto_increment,coupon_id int,uid int,is_inuse tinyint,primary key(id),key (coupon_id,uid));

insert into t3 (coupon_id,uid,is_inuse) values(16,160825,1);

insert into t3 (coupon_id,uid,is_inuse) values(16,160835,1);

insert into t3 (coupon_id,uid,is_inuse) values(16,160845,1);

insert into t3 (coupon_id,uid,is_inuse) values(16,160855,1);

insert into t3 (coupon_id,uid,is_inuse) values(16,160865,1);

root@master 22:56:  [sqltest]> select * from t3;

+----+-----------+--------+----------+

| id | coupon_id | uid    | is_inuse |

+----+-----------+--------+----------+

|  1 |        16 | 160825 |        1 |

|  2 |        16 | 160835 |        1 |

|  3 |        16 | 160845 |        1 |

|  4 |        16 | 160855 |        1 |

|  5 |        16 | 160865 |        1 |

+----+-----------+--------+----------+

5 rows in set (0.00 sec)

3.2 行记录两边间隙锁范围内无法插入

1.session 1给id=3的行记录加X锁，同时加间隙锁：160835_{160845，160845}160855

set tx_isolation='REPEATABLE-READ';

set autocommit=0;

start transaction;

select * from t3 where (uid=160845 and coupon_id=16 and is_inuse=1) for update;

+----+-----------+--------+----------+

| id | coupon_id | uid    | is_inuse |

+----+-----------+--------+----------+

|  3 |        16 | 160845 |        1 |

+----+-----------+--------+----------+

1 row in set (0.00 sec)

2.session 2插入记录，在间隙范围：160835~160845

set tx_isolation='REPEATABLE-READ';

set autocommit=0;

start transaction;

insert into t3 (coupon_id,uid,is_inuse) values (16,160840,1);

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

3.lock

root@master 23:08:  [sqltest]> select * from information_schema.innodb_locks;

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+---------------+

| lock_id           | lock_trx_id | lock_mode | lock_type | lock_table     | lock_index | lock_space | lock_page | lock_rec | lock_data     |

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+---------------+

| 49020303:1139:4:4 | 49020303    | X,GAP     | RECORD    | `sqltest`.`t3` | coupon_id  |       1139 |         4 |        4 | 16, 160845, 3 |

| 49020011:1139:4:4 | 49020011    | X         | RECORD    | `sqltest`.`t3` | coupon_id  |       1139 |         4 |        4 | 16, 160845, 3 |

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+---------------+

2 rows in set, 1 warning (0.00 sec)

4.session 2插入记录，在间隙范围：160845~160855

set tx_isolation='REPEATABLE-READ';

set autocommit=0;

start transaction;

insert into t3 (coupon_id,uid,is_inuse) values (16,160850,1);

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

5.lock

root@master 23:11:  [sqltest]> select * from information_schema.innodb_locks;

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+---------------+

| lock_id           | lock_trx_id | lock_mode | lock_type | lock_table     | lock_index | lock_space | lock_page | lock_rec | lock_data     |

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+---------------+

| 49022356:1139:4:5 | 49022356    | X,GAP     | RECORD    | `sqltest`.`t3` | coupon_id  |       1139 |         4 |        5 | 16, 160855, 4 |

| 49020011:1139:4:5 | 49020011    | X,GAP     | RECORD    | `sqltest`.`t3` | coupon_id  |       1139 |         4 |        5 | 16, 160855, 4 |

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+---------------+

2 rows in set, 1 warning (0.00 sec)

3.3 行记录间隙锁范围外可以插入

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

session 2 >insert into t3 (coupon_id,uid,is_inuse) values (16,160860,1);

Query OK, 1 row affected (0.01 sec)

3.4 update不存在的记录，也会加间隙锁

1.数据

session 1 >select * from t3;

+----+-----------+--------+----------+

| id | coupon_id | uid    | is_inuse |

+----+-----------+--------+----------+

|  1 |        16 | 160825 |        1 |

|  2 |        16 | 160835 |        1 |

|  3 |        16 | 160845 |        1 |

|  4 |        16 | 160855 |        1 |

|  5 |        16 | 160865 |        1 |

+----+-----------+--------+----------+

5 rows in set (0.00 sec)

2.update一条不存在的记录，此时gap锁范围：160835_{160845，160845}160855

set tx_isolation='REPEATABLE-READ';

set autocommit=0;

start transaction;

update t3 set is_inuse=0 where coupon_id=16 and uid=160845 and is_inuse=1;

3.在间隙范围插入新值会产生死锁

set tx_isolation='REPEATABLE-READ';

set autocommit=0;

start transaction;

insert into t3 (coupon_id,uid,is_inuse) values (16,160840,1);

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

4.lock

root@master 23:11:  [sqltest]> select * from information_schema.innodb_locks;

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+---------------+

| lock_id           | lock_trx_id | lock_mode | lock_type | lock_table     | lock_index | lock_space | lock_page | lock_rec | lock_data     |

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+---------------+

| 49023844:1139:4:4 | 49023844    | X,GAP     | RECORD    | `sqltest`.`t3` | coupon_id  |       1139 |         4 |        4 | 16, 160845, 3 |

| 49023813:1139:4:4 | 49023813    | X         | RECORD    | `sqltest`.`t3` | coupon_id  |       1139 |         4 |        4 | 16, 160845, 3 |

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+---------------+

2 rows in set, 1 warning (0.00 sec)

3.5删除索引，即使是间隙范围外的插入也会被block

1.删除索引

session 2 >drop index coupon_id on t3;

Query OK, 0 rows affected (0.09 sec)

Records: 0  Duplicates: 0  Warnings: 0

#

session 2 >commit;

Query OK, 0 rows affected (0.00 sec)

2.事务1加锁

set tx_isolation='REPEATABLE-READ';

set autocommit=0;

start transaction;

select * from t3 where (uid=160845 and coupon_id=16 and is_inuse=1) for update;

3.事务2在间隙锁范围外插入，此时不是间隙锁，而是全表锁，无法插入

set tx_isolation='REPEATABLE-READ';

set autocommit=0;

start transaction;

select * from t3 where (uid=160850 and coupon_id=16 and is_inuse=1) for update;

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

4.lock

root@master 23:27:  [sqltest]> select * from information_schema.innodb_locks;

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+-----------+

| lock_id           | lock_trx_id | lock_mode | lock_type | lock_table     | lock_index | lock_space | lock_page | lock_rec | lock_data |

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+-----------+

| 49025074:1139:3:2 | 49025074    | X         | RECORD    | `sqltest`.`t3` | PRIMARY    |       1139 |         3 |        2 | 1         |

| 49025016:1139:3:2 | 49025016    | X         | RECORD    | `sqltest`.`t3` | PRIMARY    |       1139 |         3 |        2 | 1         |

+-------------------+-------------+-----------+-----------+----------------+------------+------------+-----------+----------+-----------+

2 rows in set, 1 warning (0.00 sec)

3.6 总结

1.RR级别下，有索引，更新的时候会给行加X锁，前后加GAP锁
2.gap锁范围内无法插入新数据，避免产生幻读
3.gap锁范围外可以正常插入新数据
4.如果没有索引，更新的事务则加的就是全表锁了
5.间隙内或者间隙外都无法插入新数据

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MySQL 间隙锁

一.根据案例二：不同索引加锁顺序的问题，模拟重现死锁（详细操作步骤）

1.1表结构

1.2执行计划

1.3重现

1.4重现

1.5多查询一次取主键，解决死锁

二.根据方案三：TMS死锁分析和处理，模拟重现死锁（详细操作步骤）

三.根据案例四：MySQL间隙锁导致的Deadlock分析，模拟重现死锁（详细操作步骤）

3.1 造数据

3.2 行记录两边间隙锁范围内无法插入

3.3 行记录间隙锁范围外可以插入

3.4 update不存在的记录，也会加间隙锁

3.5删除索引，即使是间隙范围外的插入也会被block

3.6 总结

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