主从的作用：
1.可以当做一种备份方式
2.用来实现读写分离，缓解一个数据库的压力
MySQL主从备份原理：
Mysql的主从复制至少是需要两个Mysql的服务，当然Mysql的服务是可以分布在不同的服务器上，也可以在一台服务器上启动多个服务。
如果想配置成为同一台上的话，注意安装的时候，选择两个不同的prefix=路径，同时开启服务器的时候，端口不能相同。
(1)首先确保主从服务器上的Mysql版本相同（做主从服务器的原则是，MYSQL版本要相同，如果不能满足，最起码从服务器的MYSQL的版本必须高于主服务器的MYSQL版本 ）
(2)在主服务器上,设置一个从数据库的账户,使用REPLICATION SLAVE赋予权限,如:
mysql> GRANT REPLICATION SLAVE ON *.* TO 'slave001'@'192.168.0.99' IDENTIFIED BY
'123456';
Query OK, 0 rows affected (0.13 sec)
[原理]master 上提供binlog ,
slave 通过 I/O线程从 master拿取 binlog,并复制到slave的中继日志中
slave 通过 SQL线程从 slave的中继日志中读取binlog ,然后解析到slave中
主从复制大前提
需要master与slave同步，因为笔者的数据库数据量不大，所以无需考虑太多，直接把
master上的data复制到了slave上，但是如果是大的数据量，比如像taobao这个的系统
实验环境准备：
OS： CentOS5.4
Mysql:Mysql-5.0.41.tar.gz
辅助工具:SSH Secure Shell Client
两台测试IP&服务器：
Master Server: 192.168.1.2/Linux CentOS5.4/MYSQL 5.0
Slave Server: 192.168.1.3/Linux CentOS5.4/MYSQL 5.0
安装配置步骤：
1、首先在Linux环境下分配好磁盘分区以便留足MySQL数据库的备份空间
[root@vps mysql]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/simfs 30G 2.0G 29G 7% /
2、MySQL数据库的安装：
1>将Mysql-5.0.41.tar.gz通过SSH 工具 上传到Linux系统的home目录下
2>建立MySQL使用者和群组:
#groupadd mysql
#useradd -g mysql mysql
3>解压缩Mysql-5.0.41.tar.gz源码包
#cd /usr/local/sofrware
#tar zxvf Mysql-5.0.41.tar.gz
4>进入源码目录编译安装
#cd /home/Mysql-5.0.41
#./configure --prefix=/usr/local/mysql --with-charset=gbk |注:配置Mysql安装路径并且支持中文
#make |注:编译
#make install |注:编译安装
5>替换/etc/my.cnf文件,进入源码包,执行命令
#cd /home/Mysql-5.0.41
#cp support-files/my-medium.cnf /etc/my.cnf
6>完成以上操作以后进行初始化数据库,进入已经安装好的mysql目录
#cd /usr/local/mysql
#bin/mysql_install_db --user=mysql |注:--user=mysql 初始化表并且规定用mysql用户
7>设置给mysql和root用户设定访问权限 我们先进入mysql目录
#cd /usr/local/mysql
#chown -R root /usr/local/mysql 注:设定root能访问/usr/local/mysq
#chown -R mysql /usr/local/mysql/var 注:设定mysql用户能访问/usr/local/mysql/var
#chgrp -R mysql /usr/local/mysql 注:设定mysql组能够访问/usr/local/mysq
8>启动mysql,进入已经安装好的目录
#cd /usr/local/mysql
#bin/mysqld_safe --user=mysql &
9>
修改mysql数据库超级用户root的缺省密码:
/usr/local/mysql/bin/mysqladmin -u root password 'mysql'
关闭mysql服务器
cd /usr/local/mysql/bin
./mysqladmin -u root -p shutdown
10>设定开机就启动mysql,进入源码目录下
# cd /home/Mysql-5.0.41
# cp support-files/mysql.server /etc/init.d/mysql
# chmod +x /etc/init.d/mysql
# chkconfig --level 345 mysql on
# service mysql restart
Shutting down MySQL. [ 确定 ]
Starting MySQL [ 确定 ]
[root@localhost mysql]#
到这里MySQL就装好了。
3、配置MySQL5.0的复制（Replication）功能
一.将master设置为只读。
mysql> flush tables with read lock;
二.用master中的data文件夹替换slave中的data文件夹
比如 用 tar zcvf mysql_data.gz /media/raid10/mysql/3306/data
然后 mv mysql_data.gz /media/raid10/htdocs/blog/wordpress/
因为我的 /media/raid10/htdocs/blog/wordpress/ 是 Nginx 的主目录
所以可以在 slave上，用wget下载这个文件，然后 解压，并覆盖slave上的data文件
注意：覆盖之前最好备份源文件
三.配置master的my.cnf,添加以下内容
在[mysqld]配置段添加如下字段
server-id=1
log-bin=/media/raid10/mysql/3306/binlog/binlog //这里写你的binlog绝对路径名
binlog-do-db=blog //需要同步的数据库，如果没有本行，即表示同步所有的数据库
binlog-ignore-db=mysql //被忽略的数据库
这里给出我的my.cnf配置文件
[client]
character-set-server = utf8
port = 3306
socket = /tmp/mysql.sock
[mysqld]
character-set-server = utf8
replicate-ignore-db = mysql
replicate-ignore-db = test
replicate-ignore-db = information_schema
user = mysql
port = 3306
socket = /tmp/mysql.sock
basedir = /usr/local/webserver/mysql
datadir = /media/raid10/mysql/3306/data
log-error = /media/raid10/mysql/3306/mysql_error.log
pid-file = /media/raid10/mysql/3306/mysql.pid
open_files_limit = 10240
back_log = 600
max_connections = 5000
max_connect_errors = 6000
table_cache = 614
external-locking = FALSE
max_allowed_packet = 16M
sort_buffer_size = 1M
join_buffer_size = 1M
thread_cache_size = 300
#thread_concurrency = 8
query_cache_size = 20M
query_cache_limit = 2M
query_cache_min_res_unit = 2k
default-storage-engine = MyISAM
thread_stack = 192K
transaction_isolation = READ-COMMITTED
tmp_table_size = 20M
max_heap_table_size = 20M
long_query_time = 3
log-slave-updates
log-bin = /media/raid10/mysql/3306/binlog/binlog
binlog-do-db=blog
binlog-ignore-db=mysql
binlog_cache_size = 4M
binlog_format = MIXED
max_binlog_cache_size = 8M
max_binlog_size = 20M
relay-log-index = /media/raid10/mysql/3306/relaylog/relaylog
relay-log-info-file = /media/raid10/mysql/3306/relaylog/relaylog
relay-log = /media/raid10/mysql/3306/relaylog/relaylog
expire_logs_days = 30
key_buffer_size = 10M
read_buffer_size = 1M
read_rnd_buffer_size = 6M
bulk_insert_buffer_size = 4M
myisam_sort_buffer_size = 8M
myisam_max_sort_file_size = 20M
myisam_repair_threads = 1
myisam_recover
interactive_timeout = 120
wait_timeout = 120
skip-name-resolve
#master-connect-retry = 10
slave-skip-errors = 1032,1062,126,1114,1146,1048,1396
#master-host = 192.168.1.2
#master-user = username
#master-password = password
#master-port = 3306
server-id = 1
innodb_additional_mem_pool_size = 16M
innodb_buffer_pool_size = 20M
innodb_data_file_path = ibdata1:56M:autoextend
innodb_file_io_threads = 4
innodb_thread_concurrency = 8
innodb_flush_log_at_trx_commit = 2
innodb_log_buffer_size = 16M
innodb_log_file_size = 20M
innodb_log_files_in_group = 3
innodb_max_dirty_pages_pct = 90
innodb_lock_wait_timeout = 120
innodb_file_per_table = 0
#log-slow-queries = /media/raid10/mysql/3306/slow.log
#long_query_time = 10
[mysqldump]
quick
max_allowed_packet = 32M
四.在master机上为slave机添加一同步帐号
mysql> grant replication slave on *.* to 'admin'@'172.29.141.115' identified by '12345678';
mysql> flush privileges ;
五.配置slave的my.cnf,添加以下内容
注意:
1.如果mysql是5.5.3-m3 的版本，只需
在[mysqld]字段下添加如下内容
server-id=2
2.如果是5.0x的版本，需要
在[mysqld]字段下添加如下内容
server-id=2
log-bin=mysql-bin //这是同步的binlog，具体以你的binlog为准
master-host=172.29.141.112
master-user=admin
master-password=12345678
master-port=3306
master-connect-retry=60 //如果发现主服务器断线，重新连接的时间差；
replicate-do-db=blog //同步的数据库，不写本行 表示 同步所有数据库
replicate-ignore-db=mysql //不需要备份的数据库
log-slave-update
slave-skip-errors
我的mysql是5.5.3，这里给出我的slave my.cnf配置文件
[client]
character-set-server = utf8
port = 3306
socket = /tmp/mysql.sock
[mysqld]
character-set-server = utf8
replicate-ignore-db = mysql
replicate-ignore-db = test
replicate-do-db = blog
replicate-ignore-db = information_schema
user = mysql
port = 3306
socket = /tmp/mysql.sock
basedir = /usr/local/webserver/mysql
datadir = /media/raid10/mysql/3306/data
log-error = /media/raid10/mysql/3306/mysql_error.log
pid-file = /media/raid10/mysql/3306/mysql.pid
open_files_limit = 10240
back_log = 600
max_connections = 5000
max_connect_errors = 6000
table_cache = 614
external-locking = FALSE
max_allowed_packet = 16M
sort_buffer_size = 1M
join_buffer_size = 1M
thread_cache_size = 300
#thread_concurrency = 8
query_cache_size = 20M
query_cache_limit = 2M
query_cache_min_res_unit = 2k
default-storage-engine = MyISAM
thread_stack = 192K
transaction_isolation = READ-COMMITTED
tmp_table_size = 20M
max_heap_table_size = 20M
long_query_time = 3
log-slave-updates
log-bin = /media/raid10/mysql/3306/binlog/binlog
binlog_cache_size = 4M
binlog_format = MIXED
max_binlog_cache_size = 8M
max_binlog_size = 20M
relay-log-index = /media/raid10/mysql/3306/relaylog/relaylog
relay-log-info-file = /media/raid10/mysql/3306/relaylog/relaylog
relay-log = /media/raid10/mysql/3306/relaylog/relaylog
expire_logs_days = 30
key_buffer_size = 10M
read_buffer_size = 1M
read_rnd_buffer_size = 6M
bulk_insert_buffer_size = 4M
myisam_sort_buffer_size = 8M
myisam_max_sort_file_size = 20M
myisam_repair_threads = 1
myisam_recover
interactive_timeout = 120
wait_timeout = 120
skip-name-resolve
#master-connect-retry = 60
slave-skip-errors = 1032,1062,126,1114,1146,1048,1396
#master-host=172.29.141.112
#master-user = admin
#master-password = 12345678
#master-port = 3306
server-id = 2
innodb_additional_mem_pool_size = 16M
innodb_buffer_pool_size = 20M
innodb_data_file_path = ibdata1:56M:autoextend
innodb_file_io_threads = 4
innodb_thread_concurrency = 8
innodb_flush_log_at_trx_commit = 2
innodb_log_buffer_size = 16M
innodb_log_file_size = 20M
innodb_log_files_in_group = 3
innodb_max_dirty_pages_pct = 90
innodb_lock_wait_timeout = 120
innodb_file_per_table = 0
#log-slow-queries = /media/raid10/mysql/3306/slow.log
#long_query_time = 10
[mysqldump]
quick
max_allowed_packet = 32M
六.通过查看master的状态(在master上查看)，为配置slave做准备
mysql> show master status/G;
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id: 13
Current database: blog
*************************** 1. row ***************************
File: binlog.000005
Position: 592
Binlog_Do_DB: blog
Binlog_Ignore_DB: mysql
1 row in set (0.01 sec)
ERROR:
No query specified
从上面的信息，可以看出，master现在使用的binlog是binlog.000005，position是592,那么下面的slave配置必须与这个对应。
其实binlog.000005是当前master使用的binlog日志文件
position是当前master使用的binlog.000005日志文件的位置
简单理解为master正在使用哪个binlog的哪个数据行(位置)。
七.如果是5.5.3-m3版本mysql,需要启动slave后，配置与master相关对应的信息(在slave上配置)
注意，这个与第六步相对应
mysql> stop slave ;
mysql> change master to master_host='172.29.141.112', master_user='admin', master_password='12345678', master_log_file='binlog.000005', master_log_pos=488;
mysql> CHANGE MASTER TO MASTER_CONNECT_RETRY=60;
这个与5.0的配置my.cnf作用是一样的，配置成与master相对应的内容
主要是配置slave，让slave知道从master的哪个binlog上的哪个位置复制数据。所以需要知道master的ip,user_name,user_passwd,binlog,binlog_position以及多长时间连接一次master
八.开启slave
mysql> start slave;
九.解除master只读限制,并做测试
mysql> unlock tables;
mysql> use blog;
mysql> create longxibendi ( a int, b int );
十.从slave上查看
mysql> use blog;
mysql> show tables;
+-----------------------+
| Tables_in_blog |
+-----------------------+
| longxibendi |
| wp_commentmeta |
| wp_comments |
| wp_links |
| wp_options |
| wp_postmeta |
| wp_posts |
| wp_term_relationships |
| wp_term_taxonomy |
| wp_terms |
| wp_usermeta |
| wp_users |
+-----------------------+
12 rows in set (0.00 sec)
可以看到成功了！！
十一.配置过程中，可以用 show slave status/G; 在 slave上
查看 slave的复制情况
十二.如果出现什么问题，可能是防火墙的问题
/etc/init.d/iptables stop 关闭 master 上的防火墙，或者进行相应的配置
常遇到的错误与解决：
1.[mysql]ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)
这个错误，网上有很多说法，其实直接的原因是mysql服务器没有启动
之前我按照5.0x配置master-slave，然后启动slave，在连接slave,就会报这个错误
后来发现原因是，mysql slave没有启动起来，然后去查错误日志，发现以下的字段
110505 01:55:20 mysqld_safe mysqld from pid file /media/raid10/mysql/3306/mysql.pid ended
110505 02:04:41 mysqld_safe Starting mysqld daemon with databases from /media/raid10/mysql/3306/data
InnoDB: The InnoDB memory heap is disabled
InnoDB: Mutexes and rw_locks use InnoDB's own implementation
110505 2:04:41 InnoDB: highest supported file format is Barracuda.
110505 2:04:41 InnoDB Plugin 1.0.6 started; log sequence number 44338
110505 2:04:41 [ERROR] /usr/local/webserver/mysql/libexec/mysqld: unknown variable 'master-connect-retry=60'
110505 2:04:41 [ERROR] Aborting
110505 2:04:41 InnoDB: Starting shutdown...
110505 2:04:43 InnoDB: Shutdown completed; log sequence number 44348
110505 2:04:43 [Note] /usr/local/webserver/mysql/libexec/mysqld: Shutdown complete
110505 02:04:43 mysqld_safe mysqld from pid file /media/raid10/mysql/3306/mysql.pid ended
110505 02:07:44 mysqld_safe Starting mysqld daemon with databases from /media/raid10/mysql/3306/data
InnoDB: The InnoDB memory heap is disabled
InnoDB: Mutexes and rw_locks use InnoDB's own implementation
110505 2:07:44 InnoDB: highest supported file format is Barracuda.
110505 2:07:45 InnoDB Plugin 1.0.6 started; log sequence number 44348
110505 2:07:45 [ERROR] /usr/local/webserver/mysql/libexec/mysqld: unknown variable 'master-host=172.29.141.112'
110505 2:07:45 [ERROR] Aborting
从上面的ERROR，知道 master-connect-retry=60这个my.cnf中的参数有问题，后来从网上搜资料，发现，mysql5.5.3-m3版本不支持这个参数，
然后我把这个参数注释掉，又发现不支持这个参数master-host，从上面的ERROR字段可以看出来。后来，就知道，5.5.3-m3不能按5.0.x那样配置
原来不需要从my.cnf中配置master相关信息，当然server-id是必须的。其他信息，通过 在命令行中 ，登陆 mysql服务器配置。
其实server-id的作用是
第一，标识，区分不同的slave,第二，防止环备份的发生
2.Last_Error: Last_SQL_Error：等错误
这个是从 slave上，运行 show slave status/G; 得到的。出现这个问题，最根本的原因是，slave 没有与当前的master的binlog 和binlog的position对应上
也就是说，slave传输的master binlog 不与当前master正使用的binlog以及binlog的行数对应。
3.[ERROR] Slave I/O: error connecting to master 'admin@172.29.141.112:3306' - retry-time: 60 retries: 86400, Error_code: 2003
这个就是因为防火墙的问题，所以用 /etc/init.d/iptables stop 关闭防火墙就OK了。
4.遇到ERROR 2013 (HY000): Lost connection to MySQL server during query错误。
在/ect/my.cnf的[mysqld]中添加skip-name-resolve