在上两篇文章（MySQL备份与恢复之冷备，MySQL备份与恢复之真实环境使用冷备）中，我们提到了冷备和真实环境中使用冷备。那从这篇文章开始我们看下热备。显然热备和冷备是两个相对的概念，冷备是把数据库服务，比如MySQL，Oracle停下来，然后使用拷贝、打包或者压缩命令对数据目录进行备份；那么我们很容易想到热备就是在MySQL或者其他数据库服务在运行的情况下进行备份。但是，这里存在一个问题，因为生产库在运行的情况下，有对该库的读写，读写频率有可能高，也可能低，不管频率高低，总会就会造成备份出来的数据和生产库中的数据不一致的情况。热备这段时间，其他人不可以操作是不现实的，因为你总不可能终止用户访问Web程序。要解决这个问题，可以采用指定备份策略，比如哪个时间段进行备份，备份哪些数据等等，总之，保证数据的完整性和一致性，切记，备份重于一切！！！
热备可以对多个库进行备份，可以对单张表或者某几张表进行备份。但是无法同时备份多个库多个表，只有分开备份。下面我们看下热备的示意图，并进行热备模拟。
示意图
热备模拟
1、对单个库进行备份
第一步，移除LVM快照。（如果没有创建，忽略此步）
[root@serv01 data]# lvremove /dev/data/smydata Do you really want to remove active logical volume smydata? [y/n]: y Logical volume "smydata" successfully removed
第二步，设置MySQL的密码
mysql> set password=password("123456");
Query OK, 0 rows affected (0.00 sec)
第三步，查看MySQL是否启动。因为是热备，所以要求MySQL服务启动
[root@serv01 data]# /etc/init.d/mysqld status SUCCESS! MySQL running (2664)
第四步，导出单个数据库
[root@serv01 data]# cd /databackup/ #本质是导出为SQL [root@serv01 databackup]# mysqldump -uroot -p123456 --database larrydb -- MySQL dump 10.13 Distrib 5.5.29, for Linux (x86_64) -- -- Host: localhost Database: larrydb -- ------------------------------------------------------ -- Server version 5.5.29-log /*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */; /*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */; /*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */; /*!40101 SET NAMES utf8 */; /*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */; /*!40103 SET TIME_ZONE='+00:00' */; /*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */; /*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */; /*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */; /*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */; -- -- Current Database: `larrydb` -- CREATE DATABASE /*!32312 IF NOT EXISTS*/ `larrydb` /*!40100 DEFAULT CHARACTER SET latin1 */; USE `larrydb`; -- -- Table structure for table `class` -- DROP TABLE IF EXISTS `class`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!40101 SET character_set_client = utf8 */; CREATE TABLE `class` ( `cid` int(11) DEFAULT NULL, `cname` varchar(30) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1; /*!40101 SET character_set_client = @saved_cs_client */; -- -- Dumping data for table `class` -- LOCK TABLES `class` WRITE; /*!40000 ALTER TABLE `class` DISABLE KEYS */; INSERT INTO `class` VALUES (1,'linux'),(2,'oracle'); /*!40000 ALTER TABLE `class` ENABLE KEYS */; UNLOCK TABLES; -- -- Table structure for table `stu` -- DROP TABLE IF EXISTS `stu`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!40101 SET character_set_client = utf8 */; CREATE TABLE `stu` ( `sid` int(11) DEFAULT NULL, `sname` varchar(30) DEFAULT NULL, `cid` int(11) DEFAULT NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1; /*!40101 SET character_set_client = @saved_cs_client */; -- -- Dumping data for table `stu` -- LOCK TABLES `stu` WRITE; /*!40000 ALTER TABLE `stu` DISABLE KEYS */; INSERT INTO `stu` VALUES (1,'larry01',1),(2,'larry02',2); /*!40000 ALTER TABLE `stu` ENABLE KEYS */; UNLOCK TABLES; /*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */; /*!40101 SET SQL_MODE=@OLD_SQL_MODE */; /*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */; /*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */; /*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */; /*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */; /*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */; /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */; Dump completed on 2013-09-10 18:56:06 #将输出结果保存到文件中 [root@serv01 databackup]# mysqldump -uroot -p123456 --database larrydb > larrydb.sql
第五步，模拟数据丢失，进入MySQL，删除数据库
[root@serv01 data]# mysql -uroot -p123456 Welcome to the MySQL monitor. Commands end with ; or g. Your MySQL connection id is 4 Server version: 5.5.29-log Source distribution Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or 'h' for help. Type 'c' to clear the current input statement. mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | crm | | game | | hello | | larrydb | | mnt | | mysql | | performance_schema | | test | +--------------------+ 9 rows in set (0.00 sec) mysql> drop database larrydb; Query OK, 2 rows affected (0.01 sec) mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | crm | | game | | hello | | mnt | | mysql | | performance_schema | | test | +--------------------+ 8 rows in set (0.00 sec) mysql> exit Bye
第六步，导入数据
[root@serv01 databackup]# mysql -uroot -p123456第七步，登录MySQL，查看数据是否正常
[root@serv01 data]# mysql -uroot -p123456 Welcome to the MySQL monitor. Commands end with ; or g. Your MySQL connection id is 6 Server version: 5.5.29-log Source distribution Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or 'h' for help. Type 'c' to clear the current input statement. mysql> show database; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'database' at line 1 mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | crm | | game | | hello | | larrydb | | mnt | | mysql | | performance_schema | | test | +--------------------+ 9 rows in set (0.00 sec) mysql> use larrydb; Database changed mysql> select * from class; +------+--------+ | cid | cname | +------+--------+ | 1 | linux | | 2 | oracle | +------+--------+ 2 rows in set (0.00 sec) mysql> select * from stu; +------+---------+------+ | sid | sname | cid | +------+---------+------+ | 1 | larry01 | 1 | | 2 | larry02 | 2 | +------+---------+------+ 2 rows in set (0.00 sec)对多个库进行备份
第一步，查看有哪些数据库
mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | crm | | game | | hello | | larrydb | | mnt | | mysql | | performance_schema | | test | +--------------------+ 9 rows in set (0.00 sec) mysql> use game; Database changed mysql> show tables; +----------------+ | Tables_in_game | +----------------+ | country | | fight | | hero | +----------------+ 3 rows in set (0.00 sec) mysql> select * from country; +-----+---------+----------+ | cno | cname | location | +-----+---------+----------+ | 10 | caowei | luoyang | | 20 | shuhan | chengdou | | 30 | sunwu | nanjing | | 40 | houhan | luoyang | | 50 | beisong | kaifeng | | 60 | 魏国 | 洛阳 | +-----+---------+----------+ 6 rows in set (0.00 sec)第二步，备份多个库
[root@serv01 databackup]# mysqldump -uroot -p123456 --databases larrydb game > larrydb_game.sql [root@serv01 databackup]# ll larrydb_game.sql -rw-r--r--. 1 root root 6159 Sep 10 19:05 larrydb_game.sql第三步，模拟数据丢失。
mysql> drop database game; Query OK, 3 rows affected (0.01 sec) mysql> drop database larrydb; Query OK, 2 rows affected (0.00 sec) mysql> use crm; Database changed mysql> show tables; +---------------+ | Tables_in_crm | +---------------+ | test | +---------------+ 1 row in set (0.00 sec) mysql> select * from test; Empty set (0.00 sec) mysql> drop database crm; Query OK, 1 row affected (0.00 sec)第四步，恢复数据
[root@serv01 databackup]# mysql -uroot -p123456 < larrydb_game.sql第五步，查看数据是否正常
[root@serv01 data]# mysql -uroot -p123456 Welcome to the MySQL monitor. Commands end with ; or g. Your MySQL connection id is 9 Server version: 5.5.29-log Source distribution Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or 'h' for help. Type 'c' to clear the current input statement. mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | game | | hello | | larrydb | | mnt | | mysql | | performance_schema | | test | +--------------------+ 8 rows in set (0.00 sec) mysql> use game; Database changed mysql> select * from country; +-----+---------+----------+ | cno | cname | location | +-----+---------+----------+ | 10 | caowei | luoyang | | 20 | shuhan | chengdou | | 30 | sunwu | nanjing | | 40 | houhan | luoyang | | 50 | beisong | kaifeng | | 60 | 魏国 | 洛阳 | +-----+---------+----------+ 6 rows in set (0.00 sec) mysql> use larrydb; Database changed mysql> select * from class; +------+--------+ | cid | cname | +------+--------+ | 1 | linux | | 2 | oracle | +------+--------+ 2 rows in set (0.00 sec)备份所有的库
[root@serv01 databackup]# mysqldump --help | grep all-database OR mysqldump [OPTIONS] --all-databases [OPTIONS] -A, --all-databases Dump all the databases. This will be same as --databases --databases= or --all-databases), the logs will be --all-databases or --databases is given. all-databases FALSE [root@serv01 databackup]# mysqldump -uroot -p123456 --all-databases > all_databases.sql [root@serv01 databackup]# ll all_databases.sql -h -rw-r--r--. 1 root root 506K Sep 10 19:16 all_databases.sql备份某张表或者某几张表
第一步，备份某张表和某几张表
[root@serv01 databackup]# mysqldump game hero country -uroot -p123456 > game_hero_country.sql [root@serv01 databackup]# ll game_hero_country.sql -rw-r--r—. 1 root root 3955 Sep 10 19:11 game_hero_country.sql第二步，模拟数据丢失
mysql> use game; Database changed mysql> show tables; +----------------+ | Tables_in_game | +----------------+ | country | | fight | | hero | +----------------+ 3 rows in set (0.00 sec) mysql> drop table hero; Query OK, 0 rows affected (0.00 sec) mysql> drop table country; Query OK, 0 rows affected (0.00 sec)第三步，查看数据是否正常
[root@serv01 databackup]# mysql -uroot -p123456 < game_hero_country.sql ERROR 1046 (3D000) at line 22: No database selected [root@serv01 databackup]# mysql -uroot -p123456 --database game < game_hero_country.sql [root@serv01 databackup]# mysql -uroot -p123456 -e "select * from game.country" +-----+---------+----------+ | cno | cname | location | +-----+---------+----------+ | 10 | caowei | luoyang | | 20 | shuhan | chengdou | | 30 | sunwu | nanjing | | 40 | houhan | luoyang | | 50 | beisong | kaifeng | | 60 | 魏国 | 洛阳 | +-----+---------+----------+通过这两天关于MySQL热备和冷备的学习，大家是不是对MySQL备份与恢复的了解更加深入了，不管是冷备还是热备其目的都是一致的保证数据的完整性和一致性，切记，备份重于一切！！！
相信今天所学的知识在之后的学习工作中对大家有所帮助。
