MyCAT是mysql中间件，前身是阿里大名鼎鼎的Cobar，Cobar在开源了一段时间后，不了了之。于是MyCAT扛起了这面大旗，在大数据时代，其重要性愈发彰显。这篇文章主要是MyCAT的入门部署。
一、安装java
因Mycat是用java开发的，所以需要在实验环境下安装java，官方建议jdk1.7及以上版本
Java Oracle官方下载地址为：
http://www.oracle.com/technetwork/java/javase/archive-139210.html
解压jdk-7u79-linux-x64.tar.gz文件，并配置java的环境变量
# tar xvf jdk-7u79-linux-x64.tar.gz
# mv jdk1.7.0_79/ /usr/local/
编辑/etc/profile文件
# vim /etc/profile 添加如下内容
export JAVA_HOME=/usr/local/jdk1.7.0_79 export PATH=$JAVA_HOME/bin:$PATH export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
# source /etc/profile --使/etc/profile文件生效
# java -version
java version "1.7.0_79" Java(TM) SE Runtime Environment (build 1.7.0_79-b15) Java HotSpot(TM) 64-Bit Server VM (build 24.79-b02, mixed mode)
二、安装MySQL
MySQL官方下载地址如下：
http://dev.mysql.com/downloads/mysql/
里面有各种版本，包括RPM，二进制，源码包。
为了方便起见，我这里选择是RPM包
# yum install -y mysql-community-server-5.6.26-2.el5.x86_64.rpm
启动MySQL
# /etc/init.d/mysqld start
Starting mysqld (via systemctl): [ OK ]
为root账户创建密码
# mysqladmin -u root password "123456"
建议为123456，后面MyCAT配置文件schema.xml中会用到
三、安装MyCAT
创建MyCAT用户并设置密码
# useradd mycat
# passwd mycat
解压MyCAT文件
# tar xvf Mycat-server-1.5-alpha-20151221110028-linux.tar.gz
# mv mycat/ /usr/local/
设置mycat目录的属主和属组
# chown -R mycat.mycat /usr/local/mycat/
四、测试MyCAT
首先在MySQL上创建三个数据库：db1，db2，db3。
mysql> create database db1; Query OK, 1 row affected (0.00 sec)mysql
> create database db2;
Query OK, 1 row affected (0.00 sec)mysql
> create database db3;
Query OK, 1 row affected (0.00 sec)
启动mycat服务
# cd /usr/local/mycat/bin/
# ./mycat start
Starting Mycat-server...
查看mycat服务是否启动
# ps -ef |grep mycat
root 9640 7257 0 22:47 pts/3 00:00:00 grep --color=auto mycat
并没有启动
查看日志
# cd /usr/local/mycat/logs/
# cat wrapper.log
STATUS | wrapper | 2016/01/07 22:44:23 | --> Wrapper Started as Daemon STATUS | wrapper | 2016/01/07 22:44:23 | Launching a JVM... ERROR | wrapper | 2016/01/07 22:44:25 | JVM exited while loading the application. INFO | jvm 1 | 2016/01/07 22:44:25 | Error: Exception thrown by the agent : java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: MySQL-Server1: MySQL-Server1: Name or service not known STATUS | wrapper | 2016/01/07 22:44:29 | Launching a JVM... ERROR | wrapper | 2016/01/07 22:44:29 | JVM exited while loading the application. INFO | jvm 2 | 2016/01/07 22:44:29 | Error: Exception thrown by the agent : java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: MySQL-Server1: MySQL-Server1: Name or service not known STATUS | wrapper | 2016/01/07 22:44:34 | Launching a JVM... ERROR | wrapper | 2016/01/07 22:44:34 | JVM exited while loading the application. INFO | jvm 3 | 2016/01/07 22:44:34 | Error: Exception thrown by the agent : java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: MySQL-Server1: MySQL-Server1: Name or service not known STATUS | wrapper | 2016/01/07 22:44:38 | Launching a JVM... ERROR | wrapper | 2016/01/07 22:44:38 | JVM exited while loading the application. INFO | jvm 4 | 2016/01/07 22:44:38 | Error: Exception thrown by the agent : java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: MySQL-Server1: MySQL-Server1: Name or service not known STATUS | wrapper | 2016/01/07 22:44:42 | Launching a JVM... ERROR | wrapper | 2016/01/07 22:44:43 | JVM exited while loading the application. INFO | jvm 5 | 2016/01/07 22:44:43 | Error: Exception thrown by the agent : java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: MySQL-Server1: MySQL-Server1: Name or service not known FATAL | wrapper | 2016/01/07 22:44:43 | There were 5 failed launches in a row, each lasting less than 300 seconds. Giving up. FATAL | wrapper | 2016/01/07 22:44:43 | There may be a configuration problem: please check the logs. STATUS | wrapper | 2016/01/07 22:44:43 | <-- Wrapper Stopped
根据报错信息，怀疑主机名没有绑定
修改hosts文件，绑定主机名
# vim /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 192.168.244.144 MySQL-Server1
重新启动mycat服务
# cd /usr/local/mycat/bin/
# ./mycat start
这次mycat正常启动
# ps -ef |grep mycat
root 10725 1 0 22:54 ? 00:00:00 /usr/local/mycat/bin/./wrapper-linux-x86-64 /usr/local/mycat/conf/wrapper.conf wrapper.syslog.ident=mycat wrapper.pidfile=/usr/local/mycat/logs/mycat.pid wrapper.daemonize=TRUE wrapper.lockfile=/var/lock/subsys/mycat root 10881 7257 0 22:55 pts/3 00:00:00 grep --color=auto mycat
下面以Travelrecord为例，来进行插入，查询，路由分析等基本操作。
首先利用mycat连接mysql数据库
# mysql -utest -ptest -h127.0.0.1 -P8066 -DTESTDB
其中8066是mycat的监听端口，类似于mysql的3306端口，其中-u，-p，-h分别是用户名，密码和主机，-D是连接的逻辑库。
至于为什么是这些，这个跟配置文件有关。
红色部分表明连接的是mycat。
创建Travelrecord表
create table travelrecord (id bigint not null primary key,user_id varchar(100),traveldate DATE, fee decimal,days int);
插入数据
mysql> insert into travelrecord(id,user_id,traveldate,fee,days) values(1,'Victor',20160101,100,10); Query OK, 1 row affected (0.00 sec)mysql
> insert into travelrecord(id,user_id,traveldate,fee,days) values(5000001,'Job',20160102,100,10);
Query OK, 1 row affected (0.00 sec)mysql
> insert into travelrecord(id,user_id,traveldate,fee,days) values(10000001,'Slow',20160103,100,10);
Query OK, 1 row affected (0.00 sec)
至于ID为什么取三个值，这个与conf目录下autopartition-long.txt的定义有关，这个文件主要定义auto-sharding-long的规则。
# range start-end ,data node index # K=1000,M=10000. 0-500M=0 500M-1000M=1 1000M-1500M=2
我主要是测试在id取不同区间的值时，分片的效果。
下面来看看分片的效果
mysql> select * from db1.travelrecord; +----+---------+------------+------+------+ | id | user_id | traveldate | fee | days | +----+---------+------------+------+------+ | 1 | Victor | 2016-01-01 | 100 | 10 | +----+---------+------------+------+------+ 1 row in set (0.00 sec)mysql
> select * from db2.travelrecord;
+---------+---------+------------+------+------+
| id | user_id | traveldate | fee | days |
+---------+---------+------------+------+------+
| 5000001 | Job | 2016-01-02 | 100 | 10 |
+---------+---------+------------+------+------+
1 row in set (0.00 sec)mysql
> select * from db3.travelrecord;
+----------+---------+------------+------+------+
| id | user_id | traveldate | fee | days |
+----------+---------+------------+------+------+
| 10000001 | Slow | 2016-01-03 | 100 | 10 |
+----------+---------+------------+------+------+
1 row in set (0.00 sec)
果然是分配到三个不同的节点上了。
如果想看MyCAT具体会将数据分配到哪个节点上，可通过路由分析。
语法其实蛮简单，就是SQL语句前加上explain语句。
下面根据explain命令查看create语句和insert语句具体会分配到哪些Datanode上。
mysql> explain create table travelrecord (id bigint not null primary key,user_id varchar(100),traveldate DATE, fee decimal,days int); +-----------+-----------------------------------------------------------------------------------------------------------------------+ | DATA_NODE | SQL | +-----------+-----------------------------------------------------------------------------------------------------------------------+ | dn1 | create table travelrecord (id bigint not null primary key,user_id varchar(100),traveldate DATE, fee decimal,days int) | | dn2 | create table travelrecord (id bigint not null primary key,user_id varchar(100),traveldate DATE, fee decimal,days int) | | dn3 | create table travelrecord (id bigint not null primary key,user_id varchar(100),traveldate DATE, fee decimal,days int) | +-----------+-----------------------------------------------------------------------------------------------------------------------+ 3 rows in set (0.00 sec)mysql
> explain insert into travelrecord(id,user_id,traveldate,fee,days) values(1,'Victor',20160101,100,10);
+-----------+----------------------------------------------------------------------------------------------+
| DATA_NODE | SQL |
+-----------+----------------------------------------------------------------------------------------------+
| dn1 | insert into travelrecord(id,user_id,traveldate,fee,days) values(1,'Victor',20160101,100,10) |
+-----------+----------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)mysql
> explain insert into travelrecord(id,user_id,traveldate,fee,days) values(5000001,'Job',20160102,100,10);
+-----------+-------------------------------------------------------------------------------------------------+
| DATA_NODE | SQL |
+-----------+-------------------------------------------------------------------------------------------------+
| dn2 | insert into travelrecord(id,user_id,traveldate,fee,days) values(5000001,'Job',20160102,100,10) |
+-----------+-------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)mysql
> explain insert into travelrecord(id,user_id,traveldate,fee,days) values(10000001,'Slow',20160103,100,10);
+-----------+---------------------------------------------------------------------------------------------------+
| DATA_NODE | SQL |
+-----------+---------------------------------------------------------------------------------------------------+
| dn3 | insert into travelrecord(id,user_id,traveldate,fee,days) values(10000001,'Slow',20160103,100,10) |
+-----------+---------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
总结：
关于MyCAT的配置其实是蛮简单的，最主要的是熟悉各配置文件的规则。以上用户名，密码，如何分库，都是在配置文件中定义的，后续，有时间再一一详表。
关于配置文件，conf目录下主要以下三个需要熟悉。
server.xml是Mycat服务器参数调整和用户授权的配置文件
schema.xml是逻辑库定义和表以及分片定义的配置文件
rule.xml是分片规则的配置文件