MyCat：对MySQL数据库进行分库分表

本篇前提：

mycat配置正确，且能正常启动。

1、schema.xml

​​<table>​​标签：

dataNode -- 分片节点指定（取值：dataNode中的name属性值）
rule ------ 分片规则选择（取值：rule标签中的name属性值）

[root@dras-test conf]# vim schema.xml 

  1 <?xml version="1.0"?>
  2 <!DOCTYPE mycat:schema SYSTEM "schema.dtd">
  3 <mycat:schema xmlns:mycat="http://io.mycat/">
  4         <schema name="mycatdb" checkSQLschema="false" sqlMaxLimit="100">
  5                 <!-- auto sharding by id (long) -->
  6                 <table name="t_person" dataNode="dn1,dn2" rule="mod-long" />
  7                 <table name="t_user" primaryKey="id" dataNode="dn1,dn2" rule="sharding-by-murmur" /><!-- 全局表 -->
  8                 <!-- table name="province" type="global" dataNode="dn1,dn2,dn3" />
  9                 
 10                 <table name="student" dataNode="dn1,dn2" rule="auto-sharding-long-sharejoin" />
 11                 <table name="score" dataNode="dn2,dn3" rule="auto-sharding-long-sharejoin" />
 12                 <table name="score" dataNode="dn1,dn2" rule="auto-sharding-long-sharejoin" />
 13 
                 <!-- ER分片 -->
 14                 <table name="customer" dataNode="dn1,dn2,dn3" rule="auto-sharding-long-customer">
 15                         <childTable name="orders" joinKey="customer_id" parentKey="id"/>
 16                 </table -->
 17 
 18                 <table name="user" primaryKey="id" dataNode="dn1,dn2" rule="mod-long-test">
 19                         <childTable name="cell" joinKey="user_id" parentKey="id"/>
 20                         <childTable name="note" joinKey="user_id" parentKey="id"/>
 21                         <childTable name="lit" joinKey="user_id" parentKey="id"/>
 22                         <childTable name="lit_usr" joinKey="user_id" parentKey="id"/>
 23                 </table>
 24 
 25         </schema>
 26 
 27         <dataNode name="dn1" dataHost="localhost1" database="db1" />
 28         <dataNode name="dn2" dataHost="localhost1" database="db2" />
 29         <dataNode name="dn3" dataHost="localhost1" database="db3" />
 30 
 31         <dataHost name="localhost1" maxCon="500" minCon="100" balance="2"32                           writeType="1" dbType="mysql" dbDriver="native" switchType="1"  slaveThreshold="100">
 33                 <heartbeat>select user()</heartbeat>
 34 
 35                 <writeHost host="hostM1" url="localhost:3306" user="root"36                                    password="" >
 37                 </writeHost>
 38 
 39         </dataHost>
 40 </mycat:schema>

2、rule.xml

​​<tablerule>​​标签

columns—— 指定分片列的列名；

algorithm—- 选择分片算法（function标签中的name属性）

​​<function>​​标签

定义算法，class–分片算法类名及路径；

​​<count>​​ 分片数，需要分成多少片；

​​<mapFile>​​ 范围分片时使用的规则；

​​<type>​​默认值是0，表示分片列的值是整数，非0表示是字符串。

[root@dras-test conf]# vim rule.xml 

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE mycat:rule SYSTEM "rule.dtd"><mycat:rule xmlns:mycat="http://io.mycat/"><tableRule name="mod-long"><rule><columns>person_id</columns><algorithm>mod-long</algorithm></rule></tableRule><tableRule name="mod-long-test"><rule><columns>id</columns><algorithm>mod-long</algorithm></rule></tableRule><tableRule name="auto-sharding-long-customer"><rule><columns>id</columns><algorithm>auto-sharding-long-customer</algorithm>
                </rule></tableRule><tableRule name="auto-sharding-long-sharejoin"><rule><columns>id</columns><algorithm>auto-sharding-long-sharejoin</algorithm>
                </rule></tableRule><tableRule name="sharding-by-murmur"><rule><columns>uuid</columns><algorithm>murmur</algorithm></rule></tableRule><function name="mod-long" class="io.mycat.route.function.PartitionByMod"><!-- how many data nodes --><property name="count">2</property>
        </function><function name="auto-sharding-long-customer" class="io.mycat.route.function.AutoPartitionByLong"><property name="mapFile">autopartition-long.txt</property></function><function name="auto-sharding-long-sharejoin" class="io.mycat.route.function.AutoPartitionByLong"><property name="mapFile">autopartition-long-sharejoin.txt</property></function><function name="murmur" class="io.mycat.route.function.PartitionByMurmurHash"><property name="seed">0</property><!-- 默认是0 --><property name="type">1</property><!-- 默认是0, 表示integer, 非0表示string--><property name="count">2</property><!-- 要分片的数据库节点数量，必须指定，否则没法分片 --><property name="virtualBucketTimes">160</property><!-- 一个实际的数据库节点被映射为这么多虚拟节点，默认是160倍，也就是虚拟节点数是物理节点数的160倍 --><!-- <property name="weightMapFile">weightMapFile</property> 节点的权重，没有指定权重的节点默认是1。以properties文件的格式填写，以从0开始到count-1的整数值也就是节点索引为key，以节点权重值为值。>所有权重值必须是正整数，否则以1代替 --><property name="bucketMapPath">/usr/local/mycat/logs/bucketMapPath</property><!-- 用于测试时观察各物理节点与虚拟节点的分布情况，如果指定了这个属性，会把虚拟节点的murmur hash值与物理节点的映射按行输出到这个文件，没有默认值，如果不指定，就不会输出任何东西 -->
        </function></mycat:rule>

3、说明

对于以上配置文件，选择一个来说明，其他类推。

对t_person表：

在sechma.xml中：

​​<table name="t_person" dataNode="dn1,dn2" rule="mod-long" />​​

说明，将其分别存在分片节点dn1和dn2上， 分别对应实际MySQL数据库的db1和db2：

​​<dataNode name="dn1" dataHost="localhost1" database="db1" />​​

​​<dataNode name="dn2" dataHost="localhost1" database="db2" />​​

数据库db1和db2又在分片主机localhost1上，localhost1是连接的实际MySQL服务器，

​​<writeHost host="hostM1" url="localhost:3306" user="root" password="" >​​

因此，t_person表会被按照rule=’mod-long’被分别存储在实际MySQL服务器的db1和db2中。

在rule.xml中，

mod-long算法指定其分片里是id，分片算法是mod-long，对id列进行取模。

count=2，说明对2取模，

取模后值为0，存入dn1，取模后值为1，存入dn2.

4、验证

在mycat数据库中创建含id列的t_person表，插入5条数据：

[root@dras-test ~]# mysql -uroot -p123456 -h127.0.0.1 -P8066
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.29-mycat-1.6-RELEASE-20161028204710 MyCat Server (OpenCloundDB)

Copyright (c) 2000, 2013, 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> show databases;
+----------+| DATABASE |
+----------+| mycatdb  |
+----------+
1 row in set (0.00 sec)

mysql> use mycatdb;
Database changed
mysql> 
mysql> create table t_person(id int(11) primary key, name varchar(32));
Query OK, 0 rows affected (0.04 sec)mysql> desc t_person;
+-------+-------------+------+-----+---------+-------+| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   | PRI | NULL    |       || name  | varchar(32) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.01 sec)

mysql> 
mysql> insert into t_person(id,name) values(1,"Moxiao1"),(2,"Moxiao2"),(3,"Moxiao3"),(4,"Moxiao4"),(5,"Moxiao5");
Query OK, 5 rows affected (0.02 sec)
Records: 3  Duplicates: 0  Warnings: 0mysql> mysql> select * from t_person;
+----+---------+| id | name    |
+----+---------+
|  2 | Moxiao2 |
|  4 | Moxiao4 |
|  1 | Moxiao1 |
|  3 | Moxiao3 ||  5 | Moxiao5 |
+----+---------+
5 rows in set (0.04 sec)

在实际的物理MySQL服务器中，查看：

[root@dras-test conf]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 522063
Server version: 5.1.71-log Source distribution

Copyright (c) 2000, 2013, 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> show databases;
+--------------------+| Database           |
+--------------------+
| information_schema |
| db1                |
| db2                |
| db3                |
| estudy             |
| mysql              |
| test               |
| yundras            |
+--------------------+
8 rows in set (0.00 sec)mysql> select * from db1.t_person;
+----+---------+| id | name    |
+----+---------+
|  2 | Moxiao2 ||  4 | Moxiao4 |
+----+---------+
2 rows in set (0.00 sec)mysql> select * from db2.t_person;
+----+---------+| id | name    |
+----+---------+
|  1 | Moxiao1 |
|  3 | Moxiao3 ||  5 | Moxiao5 |
+----+---------+
3 rows in set (0.00 sec)

t_person表成功被mycat自动分散到db1和db2两个库的t_person中。

解决单表数据量大的问题。在以分片列为条件进行查询时，会先查找其所在的分片，缩小查找范围。

mysql> explain select * from t_person where id=3;
+-----------+-----------------------------------------------+| DATA_NODE | SQL                                           |
+-----------+-----------------------------------------------+| dn2       | SELECT * FROM t_person WHERE id = 3 LIMIT 100 |
+-----------+-----------------------------------------------+
1 row in set (0.01 sec)

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