Shulou(Shulou.com)06/01 Report--

1. Table structure

CREATE TABLE `t3` ( `id` int(11) NOT NULL, `id2` int(11) DEFAULT NULL, `id3` int(11) DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `id2` (`id2`,`id3`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

2. Data

mysql> select *from t3; +----+------+------+ | id | id2 | id3 | +----+------+------+ | 6 | 1 | 1 | | 8 | 1 | 2 | | 10 | 1 | 3 | | 7 | 4 | 4 | | 1 | 6 | 6 | | 4 | 7 | 7 | +----+------+------+ 6 rows in set (0.00 sec)

3. Insert data

mysql> insert into t3 values(11,1,3); ERROR 1062 (23000): Duplicate entry '1-3' for key 'id2'

4、show engine innodb status\G

---TRANSACTION 17751, ACTIVE 17 sec 2 lock struct(s), heap size 320, 1 row lock(s) MySQL thread id 10, OS thread handle 0xa32ffb90, query id 193 localhost root init show engine innodb status TABLE LOCK table `yzs`.` t3` trx id 17751 lock mode IX RECORD LOCKS space id 30 page no 4 n bits 80 index `id2` of table `yzs`.` t3` trx id 17751 lock mode S Record lock, heap no 7 PHYSICAL RECORD: n_fields 3; compact format; info bits 0 0: len 4; hex 80000001; asc ;; 1: len 4; hex 80000003; asc ;; 2: len 4; hex 8000000a; asc ;;

5, locking schematic diagram

6. Summary

In the unique secondary index duplicate key check, if a duplicate key is encountered, an S type next-key lock will be added to the duplicate key. Note: No matter what isolation level is added here, it is next-key lock.

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