MySQL主从复制原理、主从复制（异步）、半同步复制、基于SSL复制

概述 复制通常用来创建主节点的副本，通过添加冗余节点来保证高可用性，当然复制也可以用于其他用途，例如在从节点上进行数据读、分析等等。在横向扩展的业务中，复制很容易实施，主要表现在在利用主节点进行写操作，多个从节点进行读操作，在mysql5.5中默认

概述

复制通常用来创建主节点的副本，通过添加冗余节点来保证高可用性，当然复制也可以用于其他 用途，例如在从节点上进行数据读、分析等等。在横向扩展的业务中，复制很容易实施，主要表现在在利用主节点进行写操作，多个从节点进行读操作，在mysql5.5中默认为异步复制。

mysql 复制的异步性是指：事物首先在主节点上提交，然后复制给从节点并在从节点上应用，这样意味着在同一个时间点主从上的数据可能不一致，异步复制的好处在于它 比同步复制要快，如果对数据的一致性要求很高，还是采用同步复制较好。

mysql-5.5 开始支持semi-synchronous的复制，也叫半同步复制，目的在于事务环境下保持主从一致

mysql-5.6 开始支持延时复制。

mysql复制的原理现阶段都是一样的，master将操作记录到bin-log中，slave的一个线程去master读取bin-log，并将他们保存到relay-log中，slave的另外一个线程去重放relay-log中的操作来实现和master数据同步。

该过程的第一部分就是master记录二进制日志。在每个事务更新数据完成之前，master在二日志记录这些改变。MySQL将事务串行的写入二进制日志，即使事务中的语句都是交叉执行的。在事件写入二进制日志完成后，master通知存储引擎提交事务。
下一步就是slave将master的binary log拷贝到它自己的中继日志。首先，slave开始一个工作线程——I/O线程。I/O线程在master上打开一个普通的连接，然后开始binlog dump process。Binlog dump process从master的二进制日志中读取事件，如果已经跟上master，它会睡眠并等待master产生新的事件。I/O线程将这些事件写入中 继日志。
SQL slave thread（SQL从线程）处理该过程的最后一步。SQL线程从中继日志读取事件，并重放其中的事件而更新slave的数据，使其与master中的数 据一致。只要该线程与I/O线程保持一致，中继日志通常会位于OS的缓存中，所以中继日志的开销很小。
此外，在master中也有一个工作线程：和其它MySQL的连接一样，slave在master中打开一个连接也会使得master开始一个线程。复制 过程有一个很重要的限制——复制在slave上是串行化的，也就是说master上的并行更新操作不能在slave上并行操作。

异步主从复制配置

准备：

OS：rhel5.8_i386

SoftWare: mysql-5.5.28-linux2.6-i686.tar.gz

1、主从安装mysql

   tar xf mysql-5.5.28-linux2.6-i686.tar.gz -C /usr/local/
   # cd /usr/local/
   # ln -s mysql-5.5.28-linux2.6-i686/ mysql
   # groupadd -r mysql
   # useradd -r -g mysql -s /sbin/nologin mysql
   # mkdir /mydata/data -p
   # chown -R mysql.mysql /mydata/data/
   # chown -R root.mysql /usr/local/mysql/*
   # cp support-files/my-large.cnf /etc/my.cnf
   # cp support-files/mysql.server  /etc/init.d/mysqld
       [mysqld]
       innodb_file_per_table = 1
       datadir = /mydata/data #由于是二进制安装的mysql所以必须指定数据库目录位置
   # vim /etc/profile.d/mysqld.sh
       export PAHT=$PATH:/usr/local/mysql/bin
   # . /etc/profile.d/mysqld.sh

2、主服务器配置

    # vim /etc/my.cnf
        [mysqld]
        log-bin = master-bin
        log-bin-index = master-bin.index
        
        server-id = 1
    # scripts/mysql_install_db --user=mysql --datadir=/mydata/data/
    # service mysqld start
    # mysql
    mysql> grant replication slave on *.* to repl@'192.168.100.12' identified by 'asdasd';
    mysql> flush privileges;
    mysql> flush logs;
    mysql> show master logs;
    +-------------------+-----------+
    | Log_name          | File_size |
    +-------------------+-----------+
    | master-bin.000001 |     27326 |
    | master-bin.000002 |   1038693 |
    | master-bin.000003 |       379 |
    | master-bin.000004 |       107 |
    +-------------------+-----------+
    mysql> purge binary logs to 'master-bin.000004';

3、从服务器配置

    # vim /etc/my.cnf
        [mysqld]
        relay-log = relay-log
        relay-log-index = relay-log.index
        read-only = 1
        #innodb_file_per_table = 1
        #binlog_format=mixed
        server-id = 10
    # scripts/mysql_install_db --user=mysql --datadir=/mydata/data/
    # service mysqld start
    mysql> change master to master_host='192.168.100.11',master_user='repl',master_password='asdasd',master_log_file='master-bin.000004',master_log_pos=107;
    mysql> show slave status\G
    *************************** 1. row ***************************
                   Slave_IO_State: 
                      Master_Host: 192.168.100.11
                      Master_User: repl
                      Master_Port: 3306
                    Connect_Retry: 60
                  Master_Log_File: master-bin.000004
              Read_Master_Log_Pos: 107
                   Relay_Log_File: relay-log.000001
                    Relay_Log_Pos: 4
            Relay_Master_Log_File: master-bin.000004
                 Slave_IO_Running: No
                Slave_SQL_Running: No
                  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: 107
                  Relay_Log_Space: 107
                  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: NULL
    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: 0
    1 row in set (0.00 sec)
    mysql> start slave;
    mysql> show slave status\G
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
            ..............

至此主从异步复制就完成了

说明：

slave_id 必须是唯一的

slave没有必要开启二进制日志，但在有些情况下必须设置，如mysql级联. slave为其它slave的master,所以要设置bin_log，默认为hostname，但如果hostname改变则会出问题。

有些人可能开启了slave二进制日志，却没有设置log_slave_updates,然后查看slave的数据是否改变，这是错误的配置。所以尽量使用read_only = 1 ，防止改变数据（除了sql_thread进程）。

start slave :启动从服务器IO_Thread和SQL_Thread线程，这里也可以单独对它们进行启动

在主服务器上需设置sync-binlog = 1 ,用于事务安全

重置change master参数：

            mysql> slave stop;
            mysql> reset slave;
            mysql> change master to master_host='192.168.100.11',master_user='repl',master_password='asdasd',master_log_file='master-bin.000005',master_log_pos=107;

由于slave都会自动连接上master，当我们有时需要手动调整时可以在启动前移动slave数据目录下的master.ino和relay.info文件，或者查看variables中有无“skip-slave-start”变量，有就设置为ON

半同步复制

/usr/local/mysql/lib/plugin/semisync_master.so
/usr/local/mysql/lib/plugin/semisync_slave.so

1、主服务器配置

    mysql> install plugin rpl_semi_sync_master soname 'semisync_master.so';
    mysql> show variables like '%semi%';
    +------------------------------------+-------+
    | Variable_name                      | Value |
    +------------------------------------+-------+
    | rpl_semi_sync_master_enabled       | OFF   |
    | rpl_semi_sync_master_timeout       | 10000 |
    | rpl_semi_sync_master_trace_level   | 32    |
    | rpl_semi_sync_master_wait_no_slave | ON    |
    +------------------------------------+-------+
    mysql> set global rpl_semi_sync_master_enabled=1;
    mysql> set global rpl_semi_sync_master_timeout=1000;

2、Slave上配置

    mysql> install plugin rpl_semi_sync_slave soname 'semisync_slave.so';
    mysql> show variables like '%semi%';
    +---------------------------------+-------+
    | Variable_name                   | Value |
    +---------------------------------+-------+
    | rpl_semi_sync_slave_enabled     | OFF   |
    | rpl_semi_sync_slave_trace_level | 32    |
    +---------------------------------+-------+
    mysql> set global rpl_semi_sync_slave_enabled=1;

如果需要永久生效，请将上面几个变量分别写入master与slave中mysqld字段中。

MySQL复制过滤

MySQL复制过滤可以在Master,也可以在Slave
由于基于Master的过滤操作为影响到二进制日志的完整性，对于我们以后做及时点还原会有影响，所以我们一般不建议在Maser上做复制过滤。

1、基于数据库

    binlog-do-db           //binlog-do-db表示和哪个数据库相关的写入类、修改类指令会被写入
    binlog-ignore-db        //binlog-ignore-db表示忽略（黑名单）

2、基于表
replicate-do-table=
replicate-ignore-table=

3、对于表，还可以用通配符配置过滤
replicate-wild-do-table=
replicate-wild-ignore-table=

SSL复制

要求主从服务器各自都要有证书和私钥；默认情况下主从服务器的SSL功能是没有启用的，需要先启用。

    mysql> show variables like '%ssl%';
    +---------------+----------+
    | Variable_name | Value    |
    +---------------+----------+
    | have_openssl  | DISABLED |
    | have_ssl      | DISABLED |
    | ssl_ca        |          |
    | ssl_capath    |          |
    | ssl_cert      |          |
    | ssl_cipher    |          |
    | ssl_key       |          |
    +---------------+----------+

1、配置Master为CA证书服务器

# vim /etc/pki/tls/openssl.cnf
# cd /etc/pki/CA/
# (umask 077; openssl genrsa 1024 >private/cakey.pem)
# openssl req -new -x509 -key private/cakey.pem -out cacert.pem
    Country Name (2 letter code) [GB]:CN 
    State or Province Name (full name) [Berkshire]:GD
    Locality Name (eg, city) [Newbury]:ZS
    Organization Name (eg, company) [My Company Ltd]:NEO
    Organizational Unit Name (eg, section) []:tech
    Common Name (eg, your name or your server's hostname) []:station01.neo.com
# mkdir newcerts certs crl
# touch index.txt
# echo 01 >serial

2、为Master上的MySQL准备私钥以及颁发证书

# mkdir /usr/local/mysql/ssl
# cd /usr/local/mysql/ssl/
#(umask 077; openssl genrsa 1024 > mysql.key)
# openssl req -new -key mysql.key -out mysql.csr -days 3650
    Country Name (2 letter code) [GB]:CN
    State or Province Name (full name) [Berkshire]:GD
    Locality Name (eg, city) [Newbury]:ZS
    Organization Name (eg, company) [My Company Ltd]:NEO
    Organizational Unit Name (eg, section) []:tech
    Common Name (eg, your name or your server's hostname) []:station01.neo.com
    Email Address []:
    
    Please enter the following 'extra' attributes
    to be sent with your certificate request
    A challenge password []:
    An optional company name []:
# openssl ca -in mysql.csr -out mysql.crt
Using configuration from /etc/pki/tls/openssl.cnf
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number: 1 (0x1)
        Validity
            Not Before: May 28 02:26:17 2014 GMT
            Not After : May 28 02:26:17 2015 GMT
        Subject:
            countryName               = CN
            stateOrProvinceName       = GD
            organizationName          = NEO
            organizationalUnitName    = tech
            commonName                = station01.neo.com
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:FALSE
            Netscape Comment: 
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier: 
                A4:B7:A6:98:9F:60:08:BE:86:87:65:5F:B6:13:BC:4A:5B:D4:44:3A
            X509v3 Authority Key Identifier: 
                keyid:4F:D8:57:42:D9:39:17:7D:39:44:91:01:A4:01:DE:32:92:D6:F9:DF

Certificate is to be certified until May 28 02:26:17 2015 GMT (365 days)
Sign the certificate? [y/n]:y


1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated
# chown mysql.mysql *

3、Slave上申请证书

# mkdir /usr/local/mysql/ssl
# (umask 077; openssl genrsa 1024 >mysql.key)
# openssl req -new -key mysql.key -out mysql.csr -days 3650
    Country Name (2 letter code) [GB]:CN
    State or Province Name (full name) [Berkshire]:GD
    Locality Name (eg, city) [Newbury]:ZS
    Organization Name (eg, company) [My Company Ltd]:NEO
    Organizational Unit Name (eg, section) []:tech
    Common Name (eg, your name or your server's hostname) []:station02.neo.com
    Email Address []:
    
    Please enter the following 'extra' attributes
    to be sent with your certificate request
    A challenge password []:
    An optional company name []:
# scp mysql.csr 192.168.100.11:/root/

4、Master上为Slave签发证书

# openssl ca -in mysql.csr -out mysql.crt
Using configuration from /etc/pki/tls/openssl.cnf
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number: 2 (0x2)
        Validity
            Not Before: May 28 02:36:24 2014 GMT
            Not After : May 28 02:36:24 2015 GMT
        Subject:
            countryName               = CN
            stateOrProvinceName       = GD
            organizationName          = NEO
            organizationalUnitName    = tech
            commonName                = station02.neo.com
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:FALSE
            Netscape Comment: 
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier: 
                81:9F:5B:E7:06:D0:64:B7:E6:81:3F:98:95:71:D4:DF:C6:B8:CE:3D
            X509v3 Authority Key Identifier: 
                keyid:4F:D8:57:42:D9:39:17:7D:39:44:91:01:A4:01:DE:32:92:D6:F9:DF

Certificate is to be certified until May 28 02:36:24 2015 GMT (365 days)
Sign the certificate? [y/n]:yes


1 out of 1 certificate requests certified, commit? [y/n]yes
Write out database with 1 new entries
Data Base Updated
# scp mysql.crt 192.168.100.12:/usr/local/mysql/ssl/
# scp /etc/pki/CA/cacert.pem 192.168.100.12:/usr/local/mysql/ssl/

5、Master上编缉/etc/my.cnf启用ssl，并设置主从

# vim /etc/my.cnf
[mysqld] 
log-bin=mysql-bin 
sync_binlog = 1                          ##二进制日志 
server-id = 1                            ##此id必须全局唯一 
innodb_flush_log_at_trx_commit=1         ##每秒将事务日志立刻刷写到磁盘 
ssl                                      ##启用ssl默认是不开启的,mysql中show variables like '%ssl%'查看 
ssl_ca =/usr/local/mysql/ssl/cacert.pem      ##ca文件的位置 
ssl_cert= /usr/local/mysql/ssl/mysql.crt     ##证书文件的位置 
ssl_key = /usr/local/mysql/ssl/mysql.key     ##私钥文件的位置

6、启动mysql，并查看ssl信息

# service mysqld start 
# mysql 
mysql> show variables like '%ssl%'; 
+---------------+---------------------------------+ 
| Variable_name | Value                           | 
+---------------+---------------------------------+ 
| have_openssl  | YES                             | 
| have_ssl      | YES                             | 
| ssl_ca        | /usr/local/mysql/ssl/cacert.pem | 
| ssl_capath    |                                 | 
| ssl_cert      | /usr/local/mysql/ssl/mysql.crt  | 
| ssl_cipher    |                                 | 
| ssl_key       | /usr/local/mysql/ssl/mysql.key  | 
+---------------+---------------------------------+

7、为同步建立一最小权限账户，并要求ssl

mysql> create user 'backup_ssl'@'192.168.100.12' identified by 'redhat'; 
mysql> revoke all privileges,grant option from 'backup_ssl'@'192.168.100.12'; 
mysql> grant replication slave,replication client on *.* to 'backup_ssl'@'192.168.100.12' require ssl; 
mysql> flush privileges;
mysql> flush logs;

8、Slave上编缉/etc/my.cnf，启用ssl，并设置主从

# vim /etc/my.cnf
[mysqld] 
server-id = 2                        ##此id必须全局唯一 
##log-bin = mysql-bin                ##注释掉，从服务器不需要二进制日志
relay-log = mysql-relay              ##中继日志 
relay-log-index = mysql-ralay.index  ##中继目录 
read-only = 1                        ##从服务器只读
ssl                                  ##启用ssl默认是不开启的,mysql中show variables like '%ssl%'查看 
ssl_ca =/usr/local/mysql/ssl/cacert.pem  ##ca文件的位置 
ssl_cert= /usr/local/mysql/ssl/mysql.crt ##证书文件的位置 
ssl_key = /usr/local/mysql/ssl/mysql.key ##私钥文件的位置

9、启用mysqld并查看ssl相关信息

# servie mysqld start 
mysql> show variables like '%ssl%'; 
+---------------+---------------------------------+ 
| Variable_name | Value                           | 
+---------------+---------------------------------+ 
| have_openssl  | YES                             | 
| have_ssl      | YES                             | 
| ssl_ca        | /usr/local/mysql/ssl/cacert.pem | 
| ssl_capath    |                                 | 
| ssl_cert      | /usr/local/mysql/ssl/mysql.crt  | 
| ssl_cipher    |                                 | 
| ssl_key       | /usr/local/mysql/ssl/mysql.key  | 
+---------------+---------------------------------+

10、启动slave同步进程，连接主服务器

mysql> change master to  
    -> master_host='192.168.100.11', 
    -> master_user='backup_ssl', 
    -> master_password='redhat', 
    -> master_log_file='mysql-bin.000004', 
    -> master_ssl=1, 
    -> master_ssl_ca='/usr/local/mysql/ssl/cacert.pem', 
    -> master_ssl_cert='/usr/local/mysql/ssl/mysql.crt', 
    -> master_ssl_key='/usr/local/mysql/ssl/mysql.key'; 
mysql> start slave 
mysql> show slave status\G; ##查看slave状态

11、关注以下参数：

Slave_IO_Running: Yes                                  ##IOthread是否运行，如果为No代表slave运行不正常 
Slave_SQL_Running: Yes                                 ##SQLthread是否运行，如果为No代表slave运行不正常 
Master_SSL_CA_File: /usr/local/mysql/ssl/cacert.pem    ##是否启用了ssl 
Master_SSL_Cert: /usr/local/mysql/ssl/mysql.crt 
Master_SSL_Key: /usr/local/mysql/ssl/mysql.key 
Master_Log_File: mysql-bin.00005                       ##最后接收的主服务器的二进制 
Exec_Master_Log_Pos: 338                               ##最后执行的位置，查看master中是不是该位置 
Last_IO_Errno: 0                                       ##最后一次IOthread有没有报错