Mycat catlet跨库JOIN与全局JOIN

基于catlet的分库JOIN为数据库表按类型分库提供了很好的支持，而全局表在每个节点都有DDL实现也可以实现直接JOIN操作。当表设置为全局表后可以与任意一个表进行JOIN操作。

Mysql分库

这里我们将基础和业务分别放在不同的数据库分片上，创建m和n数据库实例名。

m基础配置数据库：包含t_user

n业务数据数据库：包含t_service

Mycat 跨库JOIN

只需要修改${MYCAT_HOME}/conf/schema.xml

<?xml version="1.0"?><!DOCTYPE mycat:schema SYSTEM "schema.dtd"><mycat:schema xmlns:mycat="http://io.mycat/">        <schema name="TESTDB" checkSQLschema="false" sqlMaxLimit="100">                <!-- auto sharding by id (long) -->                <table name="t_user"   primaryKey="u_id" autoIncrement="true"   dataNode="dn1" rule="mod-long" >                   <!--  <childTable name="t_service" primaryKey="s_id" joinKey="s_uid" parentKey="u_id"/> -->                </table>                <table name="t_service" primaryKey="s_id" autoIncrement="true"   dataNode="dn2"  rule="mod-long" />                <!-- random sharding using mod sharind rule -->                <!-- <table name="dual" primaryKey="ID" dataNode="dnx,dnoracle2" type="global"                        needAddLimit="false"/> <table name="worker" primaryKey="ID" dataNode="jdbc_dn1,jdbc_dn2,jdbc_dn3"                        rule="mod-long" /> -->                       </schema>         <!-- <dataNode name="dn1$0-743" dataHost="localhost1" database="db$0-743"                /> -->        <dataNode name="dn1" dataHost="localhost1" database="m" />        <dataNode name="dn2" dataHost="localhost1" database="n" />                <!--<dataNode name="dn4" dataHost="sequoiadb1" database="SAMPLE" />         <dataNode name="jdbc_dn1" dataHost="jdbchost" database="db1" />        <dataNode       name="jdbc_dn2" dataHost="jdbchost" database="db2" />        <dataNode name="jdbc_dn3"       dataHost="jdbchost" database="db3" /> -->        <dataHost name="localhost1" maxCon="1000" minCon="10" balance="0"                          writeType="0" dbType="mysql" dbDriver="native" switchType="1"  slaveThreshold="100">                <heartbeat>select user()</heartbeat>                <!-- can have multi write hosts -->                <writeHost host="hostM1" url="192.168.178.128:3306" user="root"   password="123456">                        <!-- can have multi read hosts -->                        <readHost host="hostS2" url="192.168.178.128:3306" user="root" password="123456" />                </writeHost>                <!-- <writeHost host="hostM2" url="localhost:3316" user="root" password="123456"/> -->        </dataHost>       </mycat:schema>                                                       

利用catlets人工智能解析工具JOIN：

/*!mycat:catlet=io.mycat.catlets.ShareJoin */SELECT * from t_service s,t_user u ON u.u_id=s.s_uid;

Mycat 全局JOIN

当表设置为全局表后可以与任意一个表进行JOIN操作。

分类全局表

一个真实的业务系统中，往往存在大量的类似字典表的表格，它们与业务表之间可能有关系，这种关系，可以理解为“标签”，而不应理解为通常的“主从关系”，这些表基本上很少变动，可以根据主键ID进行缓存，下面这张图说明了一个典型的“标签关系”图：

 

         在分片的情况下，当业务表因为规模而进行分片以后，业务表与这些附属的字典表之间的关联，就成了比较棘手的问题，考虑到字典表具有以下几个特性：

• 变动不频繁
• 数据量总体变化不大
• 数据规模不大，很少有超过数十万条记录。

鉴于此，MyCAT定义了一种特殊的表，称之为“全局表”，全局表具有以下特性：

• 全局表的插入、更新操作会实时在所有节点上执行，保持各个分片的数据一致性
• 全局表的查询操作，只从一个节点获取
• 全局表可以跟任何一个表进行JOIN操作

将字典表或者符合字典表特性的一些表定义为全局表，则从另外一个方面，很好的解决了数据JOIN的难题。通过全局表+基于E-R关系的分片策略，MyCAT可以满足80%以上的企业应用开发。

全局表配置

全局表配置比较简单，不用写 Rule 规则，如下配置即可：

<table name="company" primaryKey="ID" type="global" dataNode="dn1,dn2,dn3" />

需要注意的是，全局表每个分片节点上都要有运行创建表的 DDL 语句。

人工智能JOIN测试数据

非limit查询

boonya@ubuntu:~$ mysql -h192.168.178.128  -uroot -p123456  -P8666Warning: Using a password on the command line interface can be insecure.Welcome to the MySQL monitor.  Commands end with ; or \g.Your MySQL connection id is 5Server version: 5.6.29-mycat-1.6-RELEASE-20161028204710 MyCat Server (OpenCloundDB)Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> /*!mycat:catlet=demo.catlets.ShareJoin */SELECT * from t_service s,t_user u ON u.u_id=s.s_uid;ERROR 1064 (HY000): java.lang.ClassNotFoundException: demo.catlets.ShareJoinmysql> /*!mycat:catlet=io.mycat.catlets.ShareJoin */SELECT * from t_service s,t_user u ON u.u_id=s.s_uid;Empty set (0.15 sec)mysql> show databases;+----------+| DATABASE |+----------+| TESTDB   |+----------+1 row in set (0.00 sec)mysql> /*!mycat:catlet=io.mycat.catlets.ShareJoin */SELECT * from t_service s,t_user u ON u.u_id=s.s_uid;+------+--------------+-------+-------+--------+----------------+| s_id | s_name       | s_uid | s_uid | u_name | u_email        |+------+--------------+-------+-------+--------+----------------+|    1 | MYCATSERVICE |     1 |     1 | boonya | [e-mail] |+------+--------------+-------+-------+--------+----------------+1 row in set (0.02 sec)mysql> /*!mycat:catlet=io.mycat.catlets.ShareJoin */SELECT * from t_service s,t_user u ON u.u_id=s.s_uid;ERROR 2006 (HY000): MySQL server has gone awayNo connection. Trying to reconnect...Connection id:    15Current database: *** NONE ***+------+--------------+-------+-------+--------+-----------------+| s_id | s_name       | s_uid | s_uid | u_name | u_email         |+------+--------------+-------+-------+--------+-----------------+|    1 | MYCATSERVICE |     1 |     1 | boonya | [e-mail]  ||    2 | SHOPPING     |     2 |     2 | niuniu | [e-mail] |+------+--------------+-------+-------+--------+-----------------+2 rows in set (0.02 sec)mysql> 

JOIN查询有效。

limit查询

+------+--------------+-------+-------+--------+-----------------+| s_id | s_name       | s_uid | s_uid | u_name | u_email         |+------+--------------+-------+-------+--------+-----------------+|    1 | MYCATSERVICE |     1 |     1 | boonya | [e-mail]  ||    2 | SHOPPING     |     2 |     2 | niuniu | [e-mail] |+------+--------------+-------+-------+--------+-----------------+2 rows in set (0.37 sec)mysql> /*!mycat:catlet=io.mycat.catlets.ShareJoin */SELECT * from t_service s,t_user u ON u.u_id=s.s_uid limit 2;+------+--------------+-------+-------+--------+-----------------+| s_id | s_name       | s_uid | s_uid | u_name | u_email         |+------+--------------+-------+-------+--------+-----------------+|    1 | MYCATSERVICE |     1 |     1 | boonya | [e-mail]  ||    2 | SHOPPING     |     2 |     2 | niuniu | [e-mail] |+------+--------------+-------+-------+--------+-----------------+2 rows in set (0.06 sec)mysql> /*!mycat:catlet=io.mycat.catlets.ShareJoin */SELECT * from t_service s,t_user u ON u.u_id=s.s_uid limit 1;+------+--------------+-------+-------+--------+----------------+| s_id | s_name       | s_uid | s_uid | u_name | u_email        |+------+--------------+-------+-------+--------+----------------+|    1 | MYCATSERVICE |     1 |     1 | boonya | [e-mail] |+------+--------------+-------+-------+--------+----------------+1 row in set (0.02 sec)

最终看得到数据表对应关系如下：