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 -p123456welcome to the mysql monitor. commands end with ; or \g.your mysql connection id is 4server version: 5.5.29-log source distributioncopyright (c) 2000, 2012, oracle and/or its affiliates. all rights reserved.oracle is a registered trademark of oracle corporation and/or itsaffiliates. other names may be trademarks of their respectiveowners.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> exitbye
第六步，导入数据
[root@serv01 databackup]# mysql -uroot -p123456 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 1mysql> 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 changedmysql> 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 changedmysql> 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 changedmysql> 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 show databases;+--------------------+| database |+--------------------+| information_schema || game || hello || larrydb || mnt || mysql || performance_schema || test |+--------------------+8 rows in set (0.00 sec)mysql> use game;database changedmysql> 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 changedmysql> 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-databaseor 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 changedmysql> 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。