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: 0


mysql> 


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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