MyCat：对MySQL数据库进行分库分表
2024-08-25 03:02:46
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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