自增锁预分配ID

http://www.cnblogs.com/xpchild/p/3825309.html

mysql> show create table pp;

CREATE TABLE `pp` (
  `id` int() NOT NULL AUTO_INCREMENT,
  `name` varchar() DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=gbk 

mysql>  insert into pp(name) values('xx');
Query OK,  row affected (0.18 sec)

mysql> show create table pp;

CREATE TABLE `pp` (
  `id` int() NOT NULL AUTO_INCREMENT,
  `name` varchar() DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=gbk 

mysql> insert into pp(name) values('xx'),('xx'),('xx'),('xx');
Query OK,  rows affected (0.01 sec)
Records:   Duplicates:   Warnings: 

mysql> show create table pp;
CREATE TABLE `pp` (
  `id` int() NOT NULL AUTO_INCREMENT,
  `name` varchar() DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=gbk

mysql> insert into pp(name) select name from pp;   预分配ID值
Query OK,  rows affected (0.20 sec)
Records:   Duplicates:   Warnings: 

mysql> show create table pp;
CREATE TABLE `pp` (
  `id` int() NOT NULL AUTO_INCREMENT,
  `name` varchar() DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=gbk 

mysql> select * from pp;
+----+------+
| id | name |
+----+------+
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|  | xx   |
+----+------+
 rows in set (0.00 sec)

mysql>  insert into pp(name) values('xx');
Query OK,  row affected (0.18 sec)

mysql> select * from pp;
+----+------+
| id | name |
+----+------+
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|  | xx   |
|  | xx   |
+----+------+
 rows in set (0.00 sec)

mysql> insert into pp(name) select name from pp;
Query OK,  rows affected (0.16 sec)
Records:   Duplicates:   Warnings: 

mysql> show create table pp;
CREATE TABLE `pp` (
  `id` int() NOT NULL AUTO_INCREMENT,
  `name` varchar() DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT= DEFAULT CHARSET=gbk |
+

mysql> select * from pp;
+----+------+
| id | name |
+----+------+
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|   | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
|  | xx   |
+----+------+
 rows in set (0.01 sec)

mysql> commit;
Query OK,  rows affected (0.00 sec)

模拟崩溃

kill - `pidof mysqld`

MYSQLD再起动，再测ID

mysql> show create table pp;

CREATE TABLE `pp` (
  `id` int() NOT NULL AUTO_INCREMENT,
  `name` varchar() DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT= DEFAULT CHARSET=gbk

并没有持久化29,

select max(id) from pp   取初值 25    回退了