MySQL双主架构主库单点故障解决方案

在企业中，一般系统架构的瓶颈会出现在数据库这一部分，Mysql主从架构在很大程度上解决了这部分瓶颈，但是在Mysql主从同步的架构也存在很多问题。比如：

1. 关于数据写入部分(也就是主库)往往很难做到扩展，虽然很多大公司在逻辑业务方面就进行对数据的拆分，比如商品库存按照区域去拆分(一个区域走一个库存也就是一个主库,然后定时同步总的库存)，按照商品类型去划分(一个类型的商品走一套数据库)，但是这对于很多中小型公司来说实现起来还是比较困难的；

2. 主从同步一般都是一个主库，一旦主库出现问题,就有可能直接导致整个主从同步架构崩盘，虽然发现后也是可以慢慢恢复的，但是这个恢复时间对于很多公司来说是难以接受的。

今天的这篇博文主要给解决主库单点故障这个问题提供一个思路：

• 一台主库(我们称之为master-01)提供服务,只负责数据的写入；
• 拿出一台数据库服务器(我们称之为Master-02)资源做master-01主库的从库(之间做主从同步)；
• 两台主库之间做高可用,可以采用keepalived等方案(一定要保证master-01同时也要作为keepalived的主)；
• 程序在调用主库IP地址的地方写为高可用的VIP地址；
• 所有提供服务的从服务器与master-02进行主从同步；
• 建议采用高可用策略的时候,当master-01出现问题切换到master-02的时候,即使master-01恢复了,也不要让它去自动承接VIP地址,否则可能造成数据的混写

这样做可以在一定程度上保证主库的高可用，在一台主库down掉之后,可以在极短的时间内切换到另一台主库上(尽可能减少主库宕机对业务造成的影响)，减少了主从同步给线上主库带来的压力；但是也有几个不足的地方：

• master-02可能会一直处于空闲状态(其实完全可以让它承担一部分从库的角色来负责一部分查询请求的)；
• 这样真正提供服务的从库要等master-02先同步完了数据后才能去master-02上去同步数据，这样可能会造成一定程度的同步延迟时间的加长；
•  如果master-01一旦恢复正常，会不会导致数据写入混乱(这个可以在keepalived中设置响应的规则,让其不”夺权”，我们认为的去调整操作即可。

架构的简易图如下：

具体实施方案：

一、在所有需要提供服务的服务器上安装MySQL服务(建议源码安装)

1、yum安装依赖包

yum -y install cmake make gcc gcc-c++  ncurses-devel bison openssl-devel

2、添加MySQL所需要的用户/组

groupadd mysql
useradd -g mysql -r mysql

3、下载MySQL源码包

wget http://dev.mysql.com/get/Downloads/MySQL-5.5/mysql-5.5.36.tar.gz

4、创建MySQL安装所需要的目录

mkdir /data/mydata/{data,tmp,logs} –pv

5、解压编译安装MySQL

tar xf mysql-5.5.36.tar.gz
cd mysql-5.5.36
cmake . -DCMAKE_INSTALL_PREFIX=/usr/local/mysql \
      -DMYSQL_DATADIR=/data/mydata/data \
      -DSYSCINFDIR=/etc \
      -DWITH_INNOBASE_STORAGE_ENGINE=1 \
      -DWITH_ARCHIVE_STORAGE_ENGINE=1 \
      -DWITH_BLACKHOLE_STORAGE_ENGINE=1 \
      -DWITH_READLINE=1 \
      -DWITH_SSL=system \
      -DWITH_ZLIB=system \
      -DWITH_LIBWARP=0 \
      -DWITH_UNIX_ADDR=/tmp/mysql.sock \
      -DDEFAULT_CHARASET=uft8 \
      -DDEFAULT_COLLATTON=utf9_general_ci \
make && make install

6、为MySQL提供启动脚本

cp support-files/mysql.server /etc/rc.d/init.d/mysqld

7、为master-01主库提供配置文件(32G内存较为保守(满连接占用25G左右内存)的配置文件)

[client]
port = 3306
socket = /var/lib/mysql/mysql.sock
default-character-set = utf-8
[mysqld]
server-id = 1
port = 3306
user = mysql
basedir = /usr/local/mysql
datadir = /data/mydata/data
tmpdir = /data/mydata/tmp
socket = /var/lib/mysql/mysql.sock
skip-external-locking
skip-name-resolve
default-storage-engine = INNODB
character-set-server = utf8
wait-timeout = 100
connect_timeout = 20
interactive_timeout = 100
back_log = 300
myisam_recover
event_scheduler = on
log-bin=/data/mydata/logs/mysql-bin
binlog_format = row
max_binlog_size = 64M
binlog_cache_size = 1M
slave-net-timeout = 10
skip-slave-start
slow_query_log  = 1
long_query_time = 1
slow_query_log_file = /data/mydata/mysqllog/logs/mysql.slow
log-error = /data/mydata/mysqllog/logs/error.log
max_connections = 1000
max_user_connections = 1000
max_connect_errors = 10000
key_buffer_size = 32M     #以MyISAM为主的服务器,要调大此值
max_allowed_packet = 64M
table_cache = 4096
table_open_cache = 4096
table_definition_cache = 4096
sort_buffer_size = 512K
read_buffer_size = 512K
read_rnd_buffer_size = 512K
join_buffer_size = 512K
tmp_table_size = 64M
max_heap_table_size = 64M
query_cache_type = 0
query_cache_size = 0
bulk_insert_buffer_size = 16M
thread_cache_size = 64
thread_concurrency = 16       #CPU核数*2
thread_stack = 256K
innodb_data_home_dir = /data/mydata/data
innodb_log_group_home_dir = /data/mydata/mysqllog/logs
innodb_data_file_path = ibdata1:1G:autoextend
innodb_buffer_pool_size = 16G
innodb_buffer_pool_instances = 4
innodb_additional_mem_pool_size = 16M
innodb_log_file_size = 512M
innodb_log_buffer_size = 32M
innodb_log_files_in_group = 3
innodb_flush_log_at_trx_commit = 2
innodb_lock_wait_timeout = 10
innodb_sync_spin_loops = 40
innodb_max_dirty_pages_pct = 90
innodb_support_xa = 1
innodb_thread_concurrency = 0
innodb_thread_sleep_delay = 500
innodb_file_io_threads = 4
innodb_concurrency_tickets = 1000
log_bin_trust_function_creators = 1
innodb_flush_method = O_DIRECT
innodb_file_per_table          #是否采用单表单空间
innodb_write_io_threads = 8
innodb_read_io_threads = 8
innodb_io_capacity = 1000
innodb_file_format = Barracuda    #不开启单表单空间,此选项无效
innodb_purge_threads = 1
innodb_purge_batch_size = 32
innodb_old_blocks_pct = 75
innodb_change_buffering = all
transaction_isolation = READ-COMMITTED
[mysqldump]
quick
max_allowed_packet = 32M
[mysql]
no-auto-rehash
[myisamchk]
key_buffer_size = 64M
sort_buffer_size = 256M
read_buffer = 2M
write_buffer = 2M
[mysqlhotcopy]
interactive-timeout
[mysqld_safe]
open-files-limit = 10240

8、为master-02提供配置文件

master-02的配置文件仅需在master-01上稍作修改
server-id = 20
log_slave_updates = 1    #添加(将复制事件写入binlog,一台服务器既做主库又做从库此选项必须要开启)
replicate-same-server-id=0 #添加(防止MySQL循环更新)
relay_log_recovery = 1   #添加(MySQLrelay_log的自动修复功能)

9、为从库提供配置文件(8G)

[client]
port = 3306
socket = /var/lib/mysql/mysql.sock
default-character-set = utf8
[mysqld]
server-id = 2
port = 3306
user = mysql
basedir = /usr/local/mysql
datadir = /data/mydata/data
tmpdir  = /data/mydata/tmp
socket  = /var/lib/mysql/mysql.sock
skip-external-locking
skip-name-resolve
default-storage-engine = INNODB
character-set-server = utf8
wait-timeout = 100
connect_timeout = 20
interactive_timeout = 100
back_log = 300
myisam_recover
event_scheduler = on
log-bin=/data/mydata/logs/mysql-bin
binlog_format = row
max_binlog_size = 64M
binlog_cache_size = 1M
slave-net-timeout = 10
relay_log_recovery = 1
slow_query_log = 1
long_query_time = 1
slow_query_log_file = /data/mydata/mysqllog/logs/mysql.slow
log-error = /data/mydata/mysqllog/logs/error.log
max_connections = 500
max_user_connections = 500
max_connect_errors = 10000
key_buffer_size = 32M     #以MyISAM为主的服务器,要调大此值
max_allowed_packet = 64M
table_cache = 2048
table_open_cache = 2048
table_definition_cache = 2048
sort_buffer_size = 128K
read_buffer_size = 128K
read_rnd_buffer_size = 128K
join_buffer_size = 128K
tmp_table_size = 16M
max_heap_table_size = 16M
query_cache_type = 0
query_cache_size = 0
bulk_insert_buffer_size = 16M
thread_cache_size = 64
thread_concurrency = 4       #CPU核数*2
thread_stack = 128K
innodb_data_home_dir = /data/mydata/data
innodb_log_group_home_dir = /data/mydata/mysqllog/logs
innodb_data_file_path = ibdata1:1G:autoextend
innodb_buffer_pool_size = 2G
innodb_buffer_pool_instances = 4
innodb_additional_mem_pool_size = 4M
innodb_log_file_size = 512M
innodb_log_buffer_size = 16M
innodb_log_files_in_group = 3
innodb_flush_log_at_trx_commit = 2
innodb_lock_wait_timeout = 10
innodb_sync_spin_loops = 40
innodb_max_dirty_pages_pct = 90
innodb_support_xa = 1
innodb_thread_concurrency = 0
innodb_thread_sleep_delay = 500
innodb_file_io_threads = 4
innodb_concurrency_tickets = 1000
log_bin_trust_function_creators = 1
innodb_flush_method = O_DIRECT
innodb_file_per_table                #是否采用单表单空间
innodb_write_io_threads = 8
innodb_read_io_threads = 8
innodb_io_capacity = 1000
innodb_file_format = Barracuda     #不开启单表单空间,此选项无效
innodb_purge_threads = 1
innodb_purge_batch_size = 32
innodb_old_blocks_pct = 75
innodb_change_buffering = all
transaction_isolation = READ-COMMITTED
[mysqldump]
quick
max_allowed_packet = 32M
[mysql]
no-auto-rehash
[myisamchk]
key_buffer_size = 64M
sort_buffer_size = 256M
read_buffer = 2M
write_buffer = 2M
[mysqlhotcopy]
interactive-timeout
[mysqld_safe]
open-files-limit = 10240

10、初始化MySQL

/usr/local/mysql/scripts/mysql_install_db --user=mysql --datadir=/data/mydata/data/ --basedir=/usr/local/mysql

11、为启动脚本赋予可执行权限并启动MySQL

chmod +x /etc/rc.d/init.d/mysqld
/etc/init.d/mysqld start

二、 配置master-01

1、添加主从同步账户

mysql> grant replication slave on *.* to 'repl'@'192.168.237.%' idetified by '123456';
mysql> flush privileges;

2、查看主库的状态

mysql> show master status;
+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000009 |      652 |              |                  |
+------------------+----------+--------------+------------------+
1 row in set (0.01 sec)

3、因为这是测试环境,可以保证没数据写入,否则需要先锁表-->查看状态-->备份数据-->查看状态(保证没变)-->解锁表

三、 配置master-02

1、配置master-02为master-01的从

#若是线上有数据需要先导入数据
mysql> CHANGE MASTER TO
  -> MASTER_HOST='192.168.237.128',
  -> MASTER_PORT=3306,
  -> MASTER_USER='repl',
  -> MASTER_PASSWORD='123456',
  -> MASTER_LOG_FILE='mysql-bin.000009',
  -> MASTER_LOG_POS=652;
Query OK, 0 rows affected (0.03 sec)
mysql> start slave;
mysql> show slave status \G
   Slave_IO_Running: Yes   #确保为yes
   Slave_SQL_Running: Yes  #确保为yes

2、配置master-02的同步用户

mysql> grant replication slave on *.* to 'repl’@’192.168.237.%' identified by '123456';
mysql> flush privileges;

3、查看master-02的状态

mysql> show master status;
+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000004 |      689 |              |                  |
+------------------+----------+--------------+------------------+
1 row in set (0.00 sec)

四、从库根据上面步骤配置为master-02的从即可(为了节省篇幅不再一一赘述)

五、在master-01上创建一个数据库测试同步效果

六、去master-02跟从库上分别查看是否已经同步过数据来

好了，至此数据同步已经完成。关于keepalived实现双主高可用，我会总结在下篇keepalived实现MySQL高可用文章中，届时分享给各位。