前言：为什么MySQL要做主从复制（读写分离）?
通俗来讲，如果对数据库的读和写都在同一个数据库服务器中操作，业务系统性能会降低。
为了提升业务系统性能，优化用户体验，可以通过做主从复制（读写分离）来减轻主数据库的负载。
而且如果主数据库宕机，可快速将业务系统切换到从数据库上，可避免数据丢失。
本文提纲
一.主从复制的概念
二.配置主从复制
MySQL主从复制（读写分离）和集群的区别：
一.主从复制相关概念
（读写分离）：一般需要两台及以上数据库服务器即可（一台用于写入数据，一台用于同步主的数据并用于数据查询操作）。
局限性：
（1）配置好主从复制之后，同一张表，只能对一个服务器写操作。如果在从上执行了写操作，而之后主也操作了这张表，或导致主从不同步；据说可以配置成主主方式，但我还没有研究到。
（2）主数据库服务器宕机，需要手动将业务系统切换到从数据库服务器。无法做到高可用性（除非再通过部署keepalive做成高可用方案）。
2.集群是由N台数据库服务器组成，数据的写入和查询是随机到任意一台数据库服务器的，其他数据库服务器会自动同步数据库的操作。
任何一台数据库宕机，不会对整个集群造成大的影响。
二.配置主从复制
1.准备工作：
（1）配置MySQL主从复制（读写分离）之前，需要在主从两台服务器先安装好MySQL5.6。
（2）目前最新的MySQL5.6 GA版本是MySQL5.6.22
操作系统：centos6.3
之前有讲过源码包安装mysql5.6，这里不做解释:
主数据库IP：192.168.100.241
从数据库IP：192.168.100.242
2.修改主从数据库的my.cnf文件
先修改主配置文件模版 /etc/my.cnf（最好先备份原配置文件）
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html
[client]
port=
socket=/var/lib/mysql/mysql-.sock
default-character-set=utf8 [mysqld]
explicit_defaults_for_timestamp
sync_binlog=
server-id=
port=
socket=/var/lib/mysql/mysql-.sock
pid-file=/var/lib/mysql/mysql-.pid #user=mysql datadir=/usr/local/mysql/data
log-bin=/usr/local/mysql/data/mysqlmaster-bin
log-error=/usr/local/mysql/logs/error.log
slow_query_log_file=/usr/local/mysql/logs/slow.log
inlog_format=mixed
slow_query_log
long_query_time=
wait_timeout=
interactive_timeout=
max_connections=
max_user_connections=
max_connect_errors=
character_set_server=utf8
skip-external-locking
key_buffer_size = 128M
max_allowed_packet = 5M
table_open_cache =
sort_buffer_size = 2M
read_buffer_size = 2M
read_rnd_buffer_size = 8M
myisam_sort_buffer_size = 64M
thread_cache_size =
query_cache_size = 32M
# Try number of CPU's*2 for thread_concurrency
#thread_concurrency =
binlog-ignore-db=mysql
binlog-ignore-db=information_schema
replicate_ignore_db=mysql
replicate_ignore_db=information_schema
expire-logs-days=
skip-slave-start
skip-name-resolve
lower_case_table_names=
log_bin_trust_function_creators= # InnoDB
innodb_data_home_dir=/usr/local/mysql/data
innodb_log_group_home_dir=/usr/local/mysql/logs
innodb_data_file_path=ibdata1:128M:autoextend
innodb_buffer_pool_size=2G
innodb_log_file_size=10M
innodb_log_buffer_size=8M
innodb_lock_wait_timeout=
innodb_file_per_table
innodb_flush_log_at_trx_commit= #sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES
sql_mode=STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION,NO_AUTO_VALUE_ON_ZERO [mysqldump]
quick
max_allowed_packet = 16M [mysql]
no-auto-rehash [myisamchk]
key_buffer_size = 256K
sort_buffer_size = 256K
read_buffer = 256K
write_buffer = 256K [mysqlhotcopy]
interactive-timeout
3.从配置文件模版
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html
[client]
port=
socket=/var/lib/mysql/mysql-.sock
default-character-set=utf8 [mysqld]
sync_binlog=
server-id=
port=
socket=/var/lib/mysql/mysql-.sock
pid-file=/var/lib/mysql/mysql-.pid
user=mysql
datadir=/usr/local/mysql/data
tmpdir=/usr/local/mysql/temp/
log-bin=/usr/local/mysql/data/mysqlslave-bin
log-error=/usr/local/mysql/logs/error.log
slow_query_log_file=/usr/local/mysql/logs/slow.log
binlog_format=mixed
slow_query_log
long_query_time=
wait_timeout=
interactive_timeout=
max_connections=
max_user_connections=
max_connect_errors=
character_set_server=utf8
skip-external-locking
key_buffer_size = 128M
max_allowed_packet = 5M
table_open_cache =
sort_buffer_size = 2M
read_buffer_size = 2M
read_rnd_buffer_size = 8M
myisam_sort_buffer_size = 64M
thread_cache_size =
query_cache_size = 32M
# Try number of CPU's*2 for thread_concurrency
thread_concurrency =
binlog-ignore-db=mysql
binlog-ignore-db=information_schema
replicate_ignore_db=mysql
replicate_ignore_db=information_schema
expire-logs-days=
#skip-slave-start
skip-name-resolve
lower_case_table_names=
log_bin_trust_function_creators= # InnoDB
innodb_data_home_dir=/usr/local/mysql/data
innodb_log_group_home_dir=/usr/local/mysql/logs
innodb_data_file_path=ibdata1:128M:autoextend
innodb_buffer_pool_size=2G
innodb_log_file_size=10M
innodb_log_buffer_size=8M
innodb_lock_wait_timeout=
innodb_file_per_table
innodb_flush_log_at_trx_commit= #sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES
sql_mode=STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION,NO_AUTO_VALUE_ON_ZERO [mysqldump]
quick
max_allowed_packet = 16M [mysql]
no-auto-rehash [myisamchk]
key_buffer_size = 256K
sort_buffer_size = 256K
read_buffer = 256K
write_buffer = 256K [mysqlhotcopy]
interactive-timeout
修改之后要重启mysql：
/etc/init.d/mysql restart 或者service mysql restart (前提是安装了服务)
4.解决配置过程中遇到的问题
注意：修改my.cnf文件之后重启服务一般会遇到问题
MySQL: Starting MySQL….. ERROR! The server quit without updating PID file
1.问题
[root@localhost mysql]# /etc/rc.d/init.d/mysql status
MySQL is not running, but lock file (/var/lock/subsys/mysql[FAILED]
[root@localhost mysql]# /etc/rc.d/init.d/mysql start
Starting MySQL...The server quit without updating PID file (/usr/local/mysql/data/localhost.localdomain.pid). [FAILED]
2.原因
没有初始化权限表
[root@localhost ~]# cd /usr/local/mysql
[root@localhost mysql]# chown -R mysql.mysql .
[root@localhost mysql]# su - mysql
[mysql@localhost ~]$ cd /usr/local/mysql
[mysql@localhost mysql]$ scripts/mysql_install_db
Installing MySQL system tables...
OK
Filling help tables...
OK
To start mysqld at boot time you have to copy
support-files/mysql.server to the right place for your system
PLEASE REMEMBER TO SET A PASSWORD FOR THE MySQL root USER !
To do so, start the server, then issue the following commands:
./bin/mysqladmin -u root password 'new-password'
./bin/mysqladmin -u root -h localhost.localdomain password 'new-password'
Alternatively you can run:
./bin/mysql_secure_installation
which will also give you the option of removing the test
databases and anonymous user created by default. This is
strongly recommended for production servers.
See the manual for more instructions.
You can start the MySQL daemon with:
cd . ; ./bin/mysqld_safe &
You can test the MySQL daemon with mysql-test-run.pl
cd ./mysql-test ; perl mysql-test-run.pl
Please report any problems with the ./bin/mysqlbug script!
[mysql@localhost mysql]$ /usr/local/mysql/bin/mysqld_safe --user=mysql &
[1] 11767
[mysql@localhost mysql]$ 120502 07:01:17 mysqld_safe Logging to '/usr/local/mysql/data/localhost.localdomain.err'.
120502 07:01:17 mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/data
[mysql@localhost mysql]$ /etc/rc.d/init.d/mysql status
MySQL running (11830) [ OK ]
[mysql@localhost mysql]$ /etc/rc.d/init.d/mysql start
Starting MySQL [ OK ]
注意：master和slave的server-id一定不能相同，这里master：server-id=1，slave：server-id=2
配置时因为粗心将两个server-id=1，查了好多资料才解决。
5.设置主从同步
登录到主数据库：
(1).在主数据库上创建用于主从复制的账户（192.168.100.242换成你的从数据库IP）：
GRANT REPLICATION SLAVE ON *.* TO 'java'@'192.168.100.242' IDENTIFIED BY 'java@123456';
(2).主数据库锁表（禁止再插入数据以获取主数据库的的二进制日志坐标）:
FLUSH TABLES WITH READ LOCK;
(3).打开MySQL命令行：
#mysql -uroot -p
mysql>
SHOW MASTER STATUS; +------------------------+----------+--------------+------------------+-------------------+ |
File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set | +------------------------+----------+--------------+------------------+-------------------+ |
mysqlmaster-bin. | | | | |
+------------------------+----------+--------------+------------------+-------------------+
row in set (0.00 sec) mysql>exit;
查询结果显示：在这个例子中，二进制日志文件是mysqlmaster-bin.000002，位置是120，记录下这两个值，稍后要用到。
(4).在主数据库上使用mysqldump命令备份一下数据库：
mysqldump -uroot -p jobs > /usr/local/mysql/jobs.sql
SSH登录到从数据库：
(1).通过FTP、SFTP或其他方式，将上一步备份的主数据库快照jobs.sql上传到从数据库某个路径，例如我放在了/user/local/mysql目录下；
(2).从导入主库的备份：
#创建数空据库
CREATE DATABASE `jobs` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci
#mysqldump 恢复数据
mysql -uroot -p -B jobs </usr/local/mysql/jobs.sql
(3).给从数据库设置复制的主数据库信息（注意修改MASTER_LOG_FILE和MASTER_LOG_POS的值）
#停止从数据库的复制线程
stop slave;
#给从数据库设置复制的主数据库信息
CHANGE MASTER TO MASTER_HOST='192.168.100.241',MASTER_USER='java',MASTER_PASSWORD='java@1228',MASTER_LOG_FILE='mysqlmaster-bin.000002',
MASTER_LOG_POS=120;
#启动从数据库的复制线程
start slave;
(4).接着查询数据库的slave状态：
mysql> SHOW slave STATUS \G #如果下面两个参数都是Yes，则说明主从配置成功！ Slave_IO_Running:Yes Slave_SQL_Running:Yes
(4).接下来你可以在主数据库上创建数据库、表、插入数据，然后看从数据库是否同步了这些操作.
可能会遇到 "slave_io_running: no"问题
解决办法
mysql>stop slave ;
mysql> set GLOBAL SQL_SLAVE_SKIP_COUNTER=;
mysql>start slave ;
然后在查看主从状态
mysql> SHOW slave STATUS \G #如果下面两个参数都是Yes，则说明主从配置成功！ Slave_IO_Running:Yes Slave_SQL_Running:Yes