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上一篇：2020年MySQL数据库面试题总结

快照和复制技术的结合可以保证我们得到一个实时的在线MySQL备份解决方案。

当主库发生误操作时，只需要恢复备库上的快照，然后再根据binlog执行point-in-time的恢复即可。

下面假定一个场景：
主从架构，没有延迟，某DBA误操作：drop database
接下来我们按照以上场景进行备份恢复模拟测试

1.主库准备测试数据

mysql> create database cnfol;
Query OK, 1 row affected (0.00 sec)

mysql> create table cnfol.t (id int primary key);
Query OK, 0 rows affected (0.02 sec)

mysql> insert into cnfol.t select 1;
Query OK, 1 row affected (0.01 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into cnfol.t select 2;
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

到备库确认：

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| cnfol              |
| mysql              |
| test               |
+--------------------+
4 rows in set (0.00 sec)

mysql> select * from cnfol.t;
+----+
| id |
+----+
|  1 |
|  2 |
+----+
2 rows in set (0.00 sec)

2.加个全局读锁
在备库

mysql> flush tables with read lock;
Query OK, 0 rows affected (0.00 sec)

3.为备库所在分区创建快照

[root@localhost ~]# lvcreate --size 1G --snapshot --name backup_mysql /dev/vg/mysql
  Logical volume "backup_mysql" created

[root@localhost ~]# lvs
  LV           VG   Attr   LSize Origin Snap%  Move Log Copy%  Convert
  backup_mysql vg   swi-a- 1.00G mysql    0.00
  mysql        vg   owi-ao 2.00G

4.获取二进制日志坐标

在备库：
mysql> show master status;
+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000003 |      727 |              |                  |
+------------------+----------+--------------+------------------+
1 row in set (0.00 sec)

解锁
在备库：

mysql> unlock tables;
Query OK, 0 rows affected (0.00 sec)

6.挂载快照

[root@localhost ~]# mount /dev/vg/backup_mysql  /mnt/backup
[root@localhost ~]# cd /mnt/backup/mysql/data/cnfol/ && ls -alh
总计 32K
drwx------ 2 mysql dba 4.0K 10-14 09:57 .
drwx------ 5 mysql dba 4.0K 10-14 09:57 ..
-rw-rw---- 1 mysql dba   61 10-14 09:57 db.opt
-rw-rw---- 1 mysql dba 8.4K 10-14 09:57 t.frm
-rw-rw---- 1 mysql dba   14 10-14 09:57 t.MYD
-rw-rw---- 1 mysql dba 2.0K 10-14 10:06 t.MYI

7.主库某无经验DBA误操作

mysql> drop database cnfol;
Query OK, 1 row affected (0.05 sec)

记录下此时时间：2013-10-14 10:17:10

备库确认是否存在库cnfol:

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| test               |
+--------------------+
3 rows in set (0.01 sec)

8.备份快照

[root@localhost backup]# pwd
/mnt/backup
[root@localhost backup]# tar -jcv -f /mnt/snapshot/mysql.tar.bz2 *

这里做备份的原因有2点
* 其一，昂贵的IO，因为磁头要在快照区和系统区来回跑
* 其二，快照区空间不足，因为是COW原理

9.删除快照

[root@localhost ~]# umount /mnt/backup
[root@localhost ~]# lvremove --force /dev/vg/backup_mysql
Logical volume "backup_mysql" successfully removed

10.格式化备库所在分区

[mysql@localhost ~]$ mysqladmin -uroot -poracle shutdown
131014 10:32:40 mysqld_safe mysqld from pid file /mnt/lvm/mysql/data/localhost.localdomain.pid ended
[1]+  Done                    mysqld_safe

[root@localhost ~]# umount /mnt/lvm
[root@localhost ~]# mkfs -t ext3 /dev/vg/mysql

[root@localhost ~]# mount /dev/vg/mysql  /mnt/lvm
[root@localhost ~]# lvs
  LV    VG   Attr   LSize Origin Snap%  Move Log Copy%  Convert
  mysql vg   -wi-ao 2.00G

[root@localhost ~]# vgs
  VG   #PV #LV #SN Attr   VSize VFree
  vg     4   1   0 wz--n- 3.81G 1.81G

11.解压缩快照到备库所在分区

# tar -jxv -f /mnt/snapshot/mysql.tar.bz2 -C /mnt/lvm/
[root@localhost lvm]# pwd
/mnt/lvm

[root@localhost lvm]# ls
lost+found  mysql

12.启动MySQL

13.利用binlog执行point-in-time恢复

[mysql@localhost ~]$ mysqlbinlog --stop-datetime="2013-10-14 10:17:10" /mnt/lvm/mysql/data/mysql-bin.000003 | mysql -uroot -poracle

14.确认数据

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| cnfol              |
| mysql              |
| test               |
+--------------------+
4 rows in set (0.00 sec)

mysql> select * from cnfol.t;
+----+
| id |
+----+
|  1 |
|  2 |
+----+
2 rows in set (0.00 sec)

原文链接：http://www.jh-floor.com/shujuku/Mariadb/10070.html
作者：jh-floor

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