A brief discussion on the manifestation and value selection method of innodb_autoinc_lock_mode

mysql> show create table test_autoinc_lock\G
*************************** 1. row ***************************
    Table: test_autoinc_lock
Create Table: CREATE TABLE `test_autoinc_lock` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `a` int(11) DEFAULT NULL,
 PRIMARY KEY (`id`),
 KEY `idx_a` (`a`)
) ENGINE=InnoDB AUTO_INCREMENT=14 DEFAULT CHARSET=utf8

1 row in set (0.00 sec)
mysql> select * from test_autoinc_lock;
+----+------+
| id | a |
+----+------+
| 1 | 1 |
| 12 | 2 |
| 2 | 3 |
| 3 | 5 |
| 4 | 7 |
| 5 | 7 |
| 6 | 9 |
| 7 | 10 |
+----+------+
8 rows in set (0.00 sec)

session1
 begin;delete from test_autoinc_lock where a>7;//session2 is not submitted at this time
mysql> insert into test_autoinc_lock(a) values(100); //Gap lock exists, and the lock is waiting for session 3
mysql> insert into test_autoinc_lock(a) values(2); //This is also in the waiting state. In theory, this is not the locking range of the gap lock, so what is it waiting for? session4
mysql> select * from information_schema.innodb_trx\G
*************************** 1. row ***************************
          trx_id: 2317
         trx_state: LOCK WAIT
        trx_started: 2016-10-31 19:28:05
   trx_requested_lock_id: 2317:20
     trx_wait_started: 2016-10-31 19:28:05
        trx_weight: 1
    trx_mysql_thread_id: 9
         trx_query: insert into test_autoinc_lock(a) values(2)
    trx_operation_state: setting auto-inc lock
     trx_tables_in_use: 1
     trx_tables_locked: 1
     trx_lock_structs: 1
   trx_lock_memory_bytes: 360
      trx_rows_locked: 0
     trx_rows_modified: 0
  trx_concurrency_tickets: 0
    trx_isolation_level: REPEATABLE READ
     trx_unique_checks: 1
  trx_foreign_key_checks: 1
trx_last_foreign_key_error: NULL
 trx_adaptive_hash_latched: 0
 trx_adaptive_hash_timeout: 10000
     trx_is_read_only: 0
trx_autocommit_non_locking: 0

mysql> select * from test_autoinc_lock;
+----+------+
| id | a |
+----+------+
| 1 | 1 |
| 12 | 2 |
| 13 | 2 |
| 2 | 3 |
| 3 | 5 |
| 4 | 7 |
| 5 | 7 |
| 6 | 9 |
| 7 | 10 |
+----+------+
9 rows in set (0.00 sec) //Note that the maximum auto-increment value at this time is 13, which is the previous maximum auto-increment value + 1. In other words, session2 later released the expected auto-increment id and left 13 to session3. The application of auto-increment id values ​​is completely serial.

session1
mysql> begin;
Query OK, 0 rows affected (0.00 sec)


mysql> delete from test_autoinc_lock where a>7;
Query OK, 2 rows affected (0.00 sec)
mysql> select * from test_autoinc_lock;
+----+------+
| id | a |
+----+------+
| 1 | 1 |
| 12 | 2 |
| 13 | 2 |
| 2 | 3 |
| 3 | 5 |
| 4 | 7 |
| 5 | 7 |
| 6 | 9 |
| 7 | 10 |
+----+------+
9 rows in set (0.00 sec) //Note that the maximum auto-increment at this time is 13


session2
mysql> insert into test_autoinc_lock(a) values(100); //The same gap lock exists, and the lock is waiting for session 3
mysql> insert into test_autoinc_lock(a) values(5);
Query OK, 1 row affected (0.00 sec)


mysql> select * from test_autoinc_lock;
+----+------+
| id | a |
+----+------+
| 1 | 1 |
| 12 | 2 |
| 13 | 2 |
| 2 | 3 |
| 3 | 5 |
| 15 | 5 |
| 4 | 7 |
| 5 | 7 |
| 6 | 9 |
| 7 | 10 |
+----+------+
10 rows in set (0.00 sec) //session3 is completed directly, and note that the inserted auto-increment id value is 15, which means that the 14 expected to be assigned to session2 is skipped. You can see that the auto-increment id value is immediately assigned to session3 without having to wait for session2 to complete execution.

master session1
mysql> show variables like '%binlog_for%';
+---------------+-----------+
| Variable_name | Value |
+---------------+-----------+
| binlog_format | STATEMENT |
+---------------+-----------+
1 row in set (0.00 sec)
mysql> insert into test_autoinc_lock(a) select * from test_auto;
Query OK, 8388608 rows affected, 1 warning (29.85 sec)
Records: 8388608 Duplicates: 0 Warnings: 1


master session2 (note that session2 is executed before session1 is completed)
mysql> insert into test_autoinc_lock(a) values(2);
Query OK, 1 row affected (0.01 sec)
mysql> select * from test_autoinc_lock where a=2;
+---------+------+
| id | a |
+---------+------+
| 1376236 | 2 |
+---------+------+
1 row in set (0.00 sec)


slave session1 (you can see 1376236 primary key conflicts at this time)
mysql> show slave status\G
*************************** 1. row ***************************
        Slave_IO_State: Waiting for master to send event
         Master_Host: 10.9.73.139
         Master_User: ucloudbackup
         Master_Port: 3306
        Connect_Retry: 60
       Master_Log_File: mysql-bin.000006
     Read_Master_Log_Pos: 75823243
        Relay_Log_File:mysql-relay.000002
        Relay_Log_Pos: 541
    Relay_Master_Log_File: mysql-bin.000006
       Slave_IO_Running: Yes
      Slave_SQL_Running: No
       Replicate_Do_DB: 
     Replicate_Ignore_DB: 
      Replicate_Do_Table: 
    Replicate_Ignore_Table: 
   Replicate_Wild_Do_Table: 
 Replicate_Wild_Ignore_Table: 
          Last_Errno: 1062
          Last_Error: Error 'Duplicate entry '1376236' for key 'PRIMARY'' on query. Default database: 'test'. Query: 'insert into test_autoinc_lock(a) select * from test_auto'
         Skip_Counter: 0
     Exec_Master_Log_Pos: 75822971

SET INSERT_ID=1376236/*!*/;
#161031 21:44:31 server id 168380811 end_log_pos 75822940 CRC32 0x65797f1c Query thread_id=20 exec_time=0 error_code=0
use `test`/*!*/;
SET TIMESTAMP=1477921471/*!*/;
insert into test_autoinc_lock(a) values(2)
/*!*/;
# at 75822940
#161031 21:44:31 server id 168380811 end_log_pos 75822971 CRC32 0xbb91449d Xid = 274
COMMIT /*!*/;
# at 75822971
#161031 21:44:26 server id 168380811 end_log_pos 75823050 CRC32 0xa297b57b Query thread_id=57 exec_time=30 error_code=0
SET TIMESTAMP=1477921466/*!*/;
BEGIN
/*!*/;
# at 75823050
# at 75823082
#161031 21:44:26 server id 168380811 end_log_pos 75823082 CRC32 0xa5aa31a1 Intvar
SET INSERT_ID=1/*!*/;
#161031 21:44:26 server id 168380811 end_log_pos 75823212 CRC32 0x470282ba Query thread_id=57 exec_time=30 error_code=0
SET TIMESTAMP=1477921466/*!*/;
insert into test_autoinc_lock(a) select * from test_auto