前言
每当我们重启mysql数据库，内存里的数据就都会丢失，特别是innodb的BP里的数据，如果一刚启动并发量大的话，产生的IO将不可估量，percona xtradb有个新特性就是可以重载data page数据，也就是可以恢复重新启动前的data page数据，具体是由两个命令XTRA_LRU_DUMP、XTRA_LRU_RESTORE来执行的，它会在datadir目录下会产生一个ib_lru_dump文件，具体我们来看实例：
- mysql> show status like 'Innodb_buffer_pool_pages_data';
- +-------------------------------+-------+
- | Variable_name | Value |
- +-------------------------------+-------+
- | Innodb_buffer_pool_pages_data | 5067 |
- +-------------------------------+-------+
- 1 row in set (0.00 sec)
#我们用XTRA_LRU_DUMP来备份page data里的数据，它会在datadir下产生ib_lru_dump，注意命令调用的方式
- mysql> select * from information_schema.XTRADB_ADMIN_COMMAND /*!XTRA_LRU_DUMP*/;
- +------------------------------+
- | result_message |
- +------------------------------+
- | XTRA_LRU_DUMP was succeeded. |
- +------------------------------+
- 1 row in set (0.00 sec)
mysql> quit
Bye
[root@localhost swd]# /etc/init.d/mysqld restart
Shutting down MySQL.... [ OK ]
Starting MySQL.. [ OK ]
[root@localhost swd]# mysql
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.1.45-XinYing-log Test
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
#重启数据库之后，BP里的数据会丢失。
- mysql> show status like 'Innodb_buffer_pool_pages_data';
- +-------------------------------+-------+
- | Variable_name | Value |
- +-------------------------------+-------+
- | Innodb_buffer_pool_pages_data | 33 |
- +-------------------------------+-------+
- 1 row in set (0.00 sec)
#调用XTRA_LRU_RESTORE可以恢复重启前的BP数据
- mysql> select * from information_schema.XTRADB_ADMIN_COMMAND /*!XTRA_LRU_RESTORE*/;
- +---------------------------------+
- | result_message |
- +---------------------------------+
- | XTRA_LRU_RESTORE was succeeded. |
- +---------------------------------+
- 1 row in set (0.17 sec)
#再看是不是跟以前的是一样的啦
- mysql> show status like 'Innodb_buffer_pool_pages_data';
- +-------------------------------+-------+
- | Variable_name | Value |
- +-------------------------------+-------+
- | Innodb_buffer_pool_pages_data | 5067 |
- +-------------------------------+-------+
- 1 row in set (0.00 sec)
err日志里会有以下信息显示
091217 11:49:16 InnoDB: administration command 'XTRA_LRU_DUMP' was detected. .... 091217 11:51:44 InnoDB: administration command 'XTRA_LRU_RESTORE' was detected. 091217 11:51:45 InnoDB: reading pages based on the dumped LRU list was done. (requested: 6231, read: 6209)
