说起mysql的集群估计很多人会首先想起mysql自带的replication或者mysql-mmm。mysql-mmm其实也是基于mysql自带的replication的，不过封装的更好用一些，但是配置起来还是比较麻烦，而且对于动态增减master节点可以说是无能为力的。
偶然的情况下了解到有一个基于mysql的集群galera，除了只支持InnoDB以外，基本就没什么缺点了。大家看看官方是怎么说的：
Features
MySQL/Galera is synchronous multi-master cluster for MySQL/InnoDB database, having features like:
Synchronous replication
Active-active multi-master topology
Read and write to any cluster node
Automatic membership control, failed nodes drop from the cluster
Automatic node joining
True parallel replication, on row level
Direct client connections, native MySQL look & feel
Benefits
These features yield un-seen benefits for a DBMS clustering solution:
No slave lag
No lost transactions
Both read and write scalability
Smaller client latencies
废话少说，马上开始动手测试，测试用的OS是64位的CentOS 6。首先，添加MariaDB的软件仓库，创建文件“/etc/yum.repos.d/MariaDB.repo”，内容
# MariaDB 5.5 CentOS repository list - created 2013-11-05 06:30 UTC # http://mariadb.org/mariadb/repositories/ [mariadb] name = MariaDB baseurl = http://yum.mariadb.org/5.5/centos6-amd64 gpgkey=https://yum.mariadb.org/RPM-GPG-KEY-MariaDB gpgcheck=1
然后，安装MariaDB-Galera集成版
# yum -y install MariaDB-Galera-server.x86_64 MariaDB-client.x86_64 galera.x86_64
# cp /usr/share/mysql/wsrep.cnf /etc/my.cnf.d/
Galera默认试用4567端口同步数据，需要修改防火墙，这里为了方便直接把防火墙给关闭了
# /etc/init.d/iptables stop
MariaDB-Galera貌似没有给你提供配套的selinux配置，为了方便，直接把selinux给禁止了
# setenforce 0
既然是集群，当然不能只有一台机器
| 机器a | 192.168.56.103 |
| 机器b | 192.168.56.104 |
| 机器c | 192.168.56.105 |
修改机器a的“/etc/my.cnf.d/wsrep.cnf”，改动内容
# Full path to wsrep provider library or 'none' wsrep_provider=/usr/lib64/galera/libgalera_smm.so # Group communication system handle wsrep_cluster_address="gcomm://" # Address which donor should send State Snapshot to. # Should be the address of THIS node. DON'T SET IT TO DONOR ADDRESS!!! # (SST method dependent. Defaults to the first IP of the first interface) wsrep_sst_receive_address=192.168.56.103
因为机器a是第一个节点，wsrep_cluster_address直接填"gcomm://"就可以了。如果是要加入到某个集群，那就填集群里面随便一个节点的ip就可以，例如"gcomm://192.168.56.103:4567"。wsrep_sst_receive_address是本机用来接收同步数据的ip，默认是机器网络配置里面找到的第一个ip，如果机器有多个ip的话最好指定一下，例如“192.168.56.103”。启动mysql数据库服务
# /etc/init.d/mysql start
现在要把机器b加入到集群，同样修改配置文件“/etc/my.cnf.d/wsrep.cnf”，改动内容
# Full path to wsrep provider library or 'none' wsrep_provider=/usr/lib64/galera/libgalera_smm.so # Group communication system handle wsrep_cluster_address="gcomm://192.168.56.103:4567" # Address which donor should send State Snapshot to. # Should be the address of THIS node. DON'T SET IT TO DONOR ADDRESS!!! # (SST method dependent. Defaults to the first IP of the first interface) wsrep_sst_receive_address=192.168.56.104
启动机器b的mysql服务。
到这里集群就搭建完毕了，现在开始正式测试集群。首先，链接机器a的mysql服务，创建一个数据库和一张表，表里面有一个让mysql-mmm比较麻烦和头疼的AUTO_INCREMENT字段，顺便添加乐一个用来访问这个数据库的用户
[root@centos6 ~]# mysql -u root Welcome to the MariaDB monitor. Commands end with ; or g. Your MariaDB connection id is 3 Server version: 5.5.33a-MariaDB MariaDB Server, wsrep_23.7.6.rXXXX Copyright (c) 2000, 2013, Oracle, Monty Program Ab and others. Type 'help;' or 'h' for help. Type 'c' to clear the current input statement. MariaDB [(none)]> create database asdf; Query OK, 1 row affected (0.03 sec) MariaDB [(none)]> grant all on asdf.* to 'aauu'@'localhost' identified by '123456'; Query OK, 0 rows affected (0.00 sec) MariaDB [(none)]> use asdf; Database changed MariaDB [asdf]> create table aatt (aa int primary key auto_increment); Query OK, 0 rows affected (0.14 sec) MariaDB [asdf]> insert into aatt values (null); Query OK, 1 row affected (0.01 sec) MariaDB [asdf]> insert into aatt values (null); Query OK, 1 row affected (0.00 sec) MariaDB [asdf]> select * from aatt; +----+ | aa | +----+ | 2 | | 4 | +----+ 2 rows in set (0.00 sec)
auto_increment的步进自动变成2了，是不是很智能？现在我们去到机器b，用新建的用户名登录mysql服务，执行类似的操作
[root@centos6 ~]# mysql -u aauu -p Enter password: Welcome to the MariaDB monitor. Commands end with ; or g. Your MariaDB connection id is 4 Server version: 5.5.33a-MariaDB MariaDB Server, wsrep_23.7.6.rXXXX Copyright (c) 2000, 2013, Oracle, Monty Program Ab and others. Type 'help;' or 'h' for help. Type 'c' to clear the current input statement. MariaDB [(none)]> use asdf; Database changed MariaDB [asdf]> insert into aatt values (null); Query OK, 1 row affected (0.01 sec) MariaDB [asdf]> insert into aatt values (null); Query OK, 1 row affected (0.04 sec) MariaDB [asdf]> select * from aatt; +----+ | aa | +----+ | 2 | | 4 | | 5 | | 7 | +----+ 4 rows in set (0.00 sec)
看到没有？刚才插入的数据都在这个就没什么值得说的，厉害的是机器a上新建的用户在这里可以用！现在我们来动态把机器c加入到集群里面去
# Full path to wsrep provider library or 'none' wsrep_provider=/usr/lib64/galera/libgalera_smm.so # # Group communication system handle wsrep_cluster_address="gcomm://192.168.56.104:4567" # # Address which donor should send State Snapshot to. # # Should be the address of THIS node. DON'T SET IT TO DONOR ADDRESS!!! # # (SST method dependent. Defaults to the first IP of the first interface) wsrep_sst_receive_address=192.168.56.105
之前说过的，加入到集群里面随便一个节点的ip都可以。启动机器c的mysql服务，然后执行类似操作
[root@centos6 ~]# mysql -u root Welcome to the MariaDB monitor. Commands end with ; or g. Your MariaDB connection id is 3 Server version: 5.5.33a-MariaDB MariaDB Server, wsrep_23.7.6.rXXXX Copyright (c) 2000, 2013, Oracle, Monty Program Ab and others. Type 'help;' or 'h' for help. Type 'c' to clear the current input statement. MariaDB [(none)]> use asdf; Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed MariaDB [asdf]> insert into aatt values (null); Query OK, 1 row affected (0.00 sec) MariaDB [asdf]> insert into aatt values (null); Query OK, 1 row affected (0.00 sec) MariaDB [asdf]> select * from aatt; +----+ | aa | +----+ | 2 | | 4 | | 5 | | 7 | | 9 | | 12 | +----+ 6 rows in set (0.00 sec)
auto_increment的步进自动变成3了，看到没有？
这里我只是简单的列举了Galera的一个使用场景，还有很多它先进的地方这里没有提到，它大家可以上它的官方网站看看。
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