ER分片介绍

   以mycat逻辑库里面自带的例子,例如客户（CUSTOMER）跟订单（orders）以及订单条目（orders_item),订单条目依赖订单表，订单表依赖客户，这样客户与订单以及订单条目之间存在依赖关系，这类似业务的切分可以抽象出合适的切分规则，比如根据用户ID切分,其它相关的表都依赖于用户ID，再或者根据订单ID进行切分，总之部分业务总会可以抽象出父子关系的表。这类表适用于ER分片表，子表的记录与所关联的父表记录存放在同一个数据分片上，避免数据Join跨库操作，以order与order_item例子为例和customer与order，schema.xml中定义合适的分片配置,order,order_item根据id迕行数据切分，保证相同id的数据分到同一个分片上，在进行数据插入操作时，Mycat会获取order所在的分片，然后将order_item也插入到order所在的分片。同理order与customer也是这样关系。

1 修改 scehma.xml 添加 ER分片对应的父子表

#customer 采用rule是sharding-by-intfile，是枚举类型，类似range，可以看成是range特例情况.[root@localhost conf]# vi schema.xml<?xml version="1.0"?>
<!DOCTYPE mycat:schema SYSTEM "schema.dtd">
<mycat:schema xmlns:mycat="http://org.opencloudb/"><schema name="TESTDB" checkSQLschema="false" sqlMaxLimit="100"><table name="travelrecord" dataNode="dn1,dn2,dn3" rule="auto-sharding-long" /><table name="T_VOTE" dataNode="dn1,dn2,dn3" rule="sharding-by-murmur" /><table name="customer" primaryKey="ID" dataNode="dn1,dn2" rule="sharding-by-intfile"><childTable name="orders" primaryKey="ID" joinKey="customer_id"  parentKey="id"><childTable name="order_items" joinKey="order_id"parentKey="id" /></childTable><childTable name="customer_addr" primaryKey="ID" joinKey="customer_id"parentKey="id" /></table></schema><dataNode name="dn1" dataHost="192.168.2.130" database="db1" /><dataNode name="dn2" dataHost="192.168.2.130" database="db2" /><dataNode name="dn3" dataHost="192.168.2.130" database="db3" /><dataHost name="192.168.2.130" maxCon="1000" minCon="10" balance="0"writeType="0" dbType="mysql" dbDriver="native" switchType="1"  slaveThreshold="100"><heartbeat>select user()</heartbeat><writeHost host="hostM1" url="192.168.2.130:3306" user="root"password="root123"></writeHost></dataHost>
</mycat:schema>

2 修改 rule.xml

   #修改默认规则columns里面对应sharding_id变成id <tableRule name="sharding-by-intfile"><rule><columns>id</columns><algorithm>hash-int</algorithm></rule></tableRule><function name="hash-int"class="org.opencloudb.route.function.PartitionByFileMap"><property name="mapFile">partition-hash-int.txt</property></function>#修改func 对应的文本:定义2个值对应datanode[root@localhost conf]# vi partition-hash-int.txt10000=010010=1#reload configmysql> reload @@config;Query OK, 1 row affected (0.24 sec)Reload config success

3 在逻辑库中创建需要表

注释:创建customer和customer_addr表演示ER分片.
[root@localhost bin]# mysql -h 192.168.2.130  -P8066  -u test -ptest
Warning: Using a password on the command line interfa ce can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 17
Server version: 5.5.8-mycat-1.5.1-RELEASE-20161130213509 MyCat Server (OpenCloundDB)Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql>
mysql>
mysql> show databases;
+----------+
| DATABASE |
+----------+
| TESTDB   |
+----------+
1 row in set (0.00 sec)mysql> use TESTDB
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -ADatabase changed
mysql> show tables;
+------------------+
| Tables in TESTDB |
+------------------+
| customer         |
| customer_addr    |
| orders           |
| order_items      |
| travelrecord     |
| t_vote           |
+------------------+
6 rows in set (0.00 sec)mysql> create table customer(id int not null,customer_id int not null,datanode varchar(10),primary key(id));
Query OK, 0 rows affected (0.09 sec)mysql>  create table customer_addr(id int not null,customer_id int not null,customer_addr varchar(200),datanode varchar(10),primary key(id));
Query OK, 0 rows affected (0.04 sec)

插入数据到customer和customer_addr表

a:插入数据到customer

mysql> insert into customer(id,customer_id,datanode) values(10000,1,database());
Query OK, 1 row affected (0.07 sec)

对应的日志

可以看到写入到db1

b:插入数据到 customer_addr

mysql> insert into customer_addr (id, customer_id, customer_addr, datanode) values (10000, 10000, 'shanghai', DATABASE())
Query OK, 1 row affected (0.11 sec)

对应的日志

c:继续插入数据到dn2

mysql> insert into customer(id,customer_id,datanode) values(10010,2,database());
Query OK, 1 row affected (0.01 sec)mysql> insert into customer_addr(id,customer_id,customer_addr,datanode) values(10010,10010,'chengdu',database());
Query OK, 1 row affected (0.11 sec)

4 验证ER分片

#获取全部数据
mysql> explain select customer.id,customer.customer_id,customer.datanode,customer_addr.customer_addr from customer,customer_addr where customer.id=customer_addr.customer_id;
+-----------+-----------------------------------------------------------+
| DATA_NODE | SQL                                                       |
+-----------+-----------------------------------------------------------+
| dn1       |select customer.id,customer.customer_id,customer.datanode, |
|           |       customer_addr.customer_addr                         |
|           |from customer,customer_addr                                |
|           |where customer.id=customer_addr.customer_id;               |
|           |                                                           |
| dn2       |select customer.id,customer.customer_id,customer.datanode, |
|           |       customer_addr.customer_addr                         |
|           |from customer,customer_addr                                |
|           |where customer.id=customer_addr.customer_id;               |
+-----------+-----------------------------------------------------------+

对应的日志

由上可知走的是全部路由

#获取单个分片上的数据
mysql> explain select customer.id,customer.customer_id,customer.datanode,customer_addr.customer_addr from customer,customer_addr where customer.id=customer_addr.customer_id and customer.id=10000;
+-----------+--------------------------------------------------------------------+
| DATA_NODE | SQL                                                                |
+-----------+--------------------------------------------------------------------+
| dn1       | select customer.id,customer.customer_id,customer.datanode,         |
|           |        customer_addr.customer_addr                                 |
|           | from customer,customer_addr                                        |
|           | where customer.id=customer_addr.customer_id and customer.id=10000  |
+-----------+--------------------------------------------------------------------+
1 row in set (0.00 sec)

由上可知路由到了dn1上