主从复制主要用途：
1.灾备切换
2.读写分离
3.备份，避免影响业务
4.高可用和故障切换
5.mysql测试升级
首先，异步主从复制主要步骤：
1.主库中开启log_bin
2.全备份主库
3.授权（grant replication slave on . ）
4.配置复制，并启动（change master to）
5.查看主从复制信息
异步主从复制存在的主要问题：
1.主机宕机后，数据可能丢失
2.从库只有一个sql thread，当主库有大量写入时候，从库容易丢失数据
异步复制的演示：
第一步：主库中开启log_bin=1,在my.cnf文件中设置，这里就不详细介绍了。
第二步：用mysqldump进行主库全备份
[root@VM_85_42_centos downloads]# ps -ef |grep mysqld #查看配置位置
root 5307 1 0 Apr03 ? 00:00:00 /bin/sh /usr/local/mysql56/bin/mysqld_safe --defaults-file=/mysqldata/my.cnf
mysql 5539 5307 0 Apr03 ? 00:00:50 /usr/local/mysql56/bin/mysqld --defaults-file=/mysqldata/my.cnf --basedir=/usr/local/mysql56 --datadir=/mysqldata/node1 --plugin-dir=/usr/local/mysql56/lib/plugin --user=mysql --log-error=/mysqldata/node1/VM_85_42_centos.err --pid-file=/mysqldata/node1/VM_85_42_centos.pid --socket=/tmp/mysql.sock --port=6000
root 13332 20569 0 23:19 pts/0 00:00:00 grep --color=auto mysqld
[root@VM_85_42_centos downloads]# mysqldump -uroot -p --socket=/tmp/mysql.sock --single-transaction -A --master-data=1 > all_data.sql
[root@VM_85_42_centos downloads]# mysqldump -uroot -p --socket=/tmp/mysql.sock --single-transaction -A --master-data=1 > all_data.sql
Enter password:
[root@VM_85_42_centos downloads]# ls
all_data.sql使用远程登入从库myqsl
mysql -utest -ptest -h(从库IP) -P（端口号）
登入从库后用
mysql>source all_data.sql; # 导入主库第三步：主库授权用户
grant replication slave on *.* to replication@'(从库IP)' identified by 'replication';
从库配置复制
CHANGE MASTER TO
MASTER_HOST='主库IP',
MASTER_USER='replication',
MASTER_PASSWORD='replication',
MASTER_PORT=（根据my.cnf配置端口）,
MASTER_LOG_FILE='master2-bin.XXX',
MASTER_LOG_POS=X,
MASTER_CONNECT_RETRY=X; #等一系列参数
我的实例配置
mysql> change master to
MASTER_HOST='119.29.215.56',
MASTER_USER='replication',
MASTER_PASSWORD='replication',
MASTER_PORT=6000,
MASTER_LOG_FILE='mysql-bin.000002', MASTER_LOG_POS=630；
#MASTER_LOG_FILE，MASTER_LOG_POS参数记录在刚才的 all_data.sql，可以用less命令查看。
配置完成以后启动：
mysql> start stave;
mysql> show slave status \G #是否启动看running是yes
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 119.29.215.56
Master_User: repl
Master_Port: 6000
Connect_Retry: 60
Master_Log_File: mysql-bin.000002
Read_Master_Log_Pos: 952
Relay_Log_File: VM_91_3_centos-relay-bin.000002
Relay_Log_Pos: 605
Relay_Master_Log_File: mysql-bin.000002
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 952
Relay_Log_Space: 787
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 6000
Master_UUID: cf441ef0-181b-11e7-b566-525400ef16de
Master_Info_File: /mysqldata/node1/master.info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set:
Auto_Position: 0
1 row in set (0.00 sec)
上面各类参数都是可以配置的，需要查看文档
