浅谈innodb_autoinc_lock_mode的表现形式和选值参考方法

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;//这时未提交
session2
mysql> insert into test_autoinc_lock(a) values(100);//gap锁的存在，这时处于锁等待
session3
mysql> insert into test_autoinc_lock(a) values(2);//这时同样处于等待状态，理论上这个不是gap锁的锁定范围，那么它是在等什么呢
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)//注意看这时的最大自增值是13，也就是之前自增最大值上+1，也就是说session2后来释放了预计生成的自增id，将13留给了session3，自增id值的申请完全是串行顺序的。

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)//注意看这时的最大自增值是13


session2
mysql> insert into test_autoinc_lock(a) values(100);//同样gap锁的存在，这时处于锁等待
session3
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直接完成了，并且注意观察自增id值是15，也就是跳过了预计分配给session2的14，可以看到自增id值立马就分配给了session3，而不必等session2执行完成

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（注意session2在session1执行完成之前执行）
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（这时可看到1376236主键冲突）
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