Mycat之——取模分片

转载请注明出处：http://blog.csdn.net/l1028386804/article/details/77150670

一、简单描述

取模分片，就是根据数据表的某一个字段，通常是某一个整数型的字段，对其进行十进制的求模运算，将运算结果作为Mycat的路由结果，具体规则如下：

此分片算法根据id进行十进制求模运算，相比固定的分片hash，这种分片算法在批量插入时会增加事务一致性的难度。

二、实现取模分片

1、配置rule.xml

在rule.xml中添加如下配置

<tableRule name="mod-long"><rule><columns>id</columns><algorithm>mod-long</algorithm></rule>
</tableRule>
<function name="mod-long" class="org.opencloudb.route.function.PartitionByMod"><!-- how many data nodes --><property name="count">3</property>
</function>

2、配置schema.xml

<?xml version="1.0"?>
<!DOCTYPE mycat:schema SYSTEM "schema.dtd">
<mycat:schema xmlns:mycat="http://org.opencloudb/" ><schema name="lyzdb" checkSQLschema="false" sqlMaxLimit="100"><!-- global table is auto cloned to all defined data nodes ,so can join with any table whose sharding node is in the same data node --><table name="t_user" primaryKey="id" dataNode="dn1,dn2,dn3" rule="mod-long"/></schema><!-- <dataNode name="dn1$0-743" dataHost="localhost1" database="db$0-743" /> --><dataNode name="dn1" dataHost="localhost1" database="db1" /><dataNode name="dn2" dataHost="localhost1" database="db2" /><dataNode name="dn3" dataHost="localhost1" database="db3" /><!--<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="192.168.209.137:3306" user="root" password="root"></writeHost><!--<writeHost host="hostS1" url="localhost:3316" user="root"--><!--password="123456" />--><!-- <writeHost host="hostM2" url="localhost:3316" user="root" password="123456"/> --></dataHost>
</mycat:schema>

至此，Mycat的配置工作就算完成了，下面，我们一起来测试下Mycat的路由结果。

三、测试路由结果

1、创建数据表

mysql> explain CREATE TABLE t_user (ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,name VARCHAR(64),sex VARCHAR(2), CREATE_TIME DATETIME);
+-----------+------------------------------------------------------------------------------------------------------------------------+
| DATA_NODE | SQL                                                                                                                    |
+-----------+------------------------------------------------------------------------------------------------------------------------+
| dn1       | CREATE TABLE t_user (ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,name VARCHAR(64),sex VARCHAR(2), CREATE_TIME DATETIME) |
| dn2       | CREATE TABLE t_user (ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,name VARCHAR(64),sex VARCHAR(2), CREATE_TIME DATETIME) |
| dn3       | CREATE TABLE t_user (ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,name VARCHAR(64),sex VARCHAR(2), CREATE_TIME DATETIME) |
+-----------+------------------------------------------------------------------------------------------------------------------------+
3 rows in set (0.00 sec)mysql> CREATE TABLE t_user (ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,name VARCHAR(64),sex VARCHAR(2), CREATE_TIME DATETIME);
Query OK, 0 rows affected (0.21 sec)

Mycat日志如下：

08/13 21:44:36.871  DEBUG [$_NIOREACTOR-0-RW] (NonBlockingSession.java:113) -ServerConnection [id=1, schema=lyzdb, host=192.168.209.1, user=lyz,txIsolation=3, autocommit=true, schema=lyzdb]CREATE TABLE t_user (ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,name VARCHAR(64),sex VARCHAR(2), CREATE_TIME DATETIME), route={1 -> dn1{CREATE TABLE t_user (ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,name VARCHAR(64),sex VARCHAR(2), CREATE_TIME DATETIME)}2 -> dn2{CREATE TABLE t_user (ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,name VARCHAR(64),sex VARCHAR(2), CREATE_TIME DATETIME)}3 -> dn3{CREATE TABLE t_user (ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,name VARCHAR(64),sex VARCHAR(2), CREATE_TIME DATETIME)}
} rrs

由此可见，当创建数据表时，Mycat将SQL路由到所有的数据节点。

2、录入数据

mysql> explain insert into t_user(id,name, sex, CREATE_TIME) values(1,'lyz01', 'n', NOW());
+-----------+-----------------------------------------------------------------------------+
| DATA_NODE | SQL                                                                         |
+-----------+-----------------------------------------------------------------------------+
| dn2       | insert into t_user(id,name, sex, CREATE_TIME) values(1,'lyz01', 'n', NOW()) |
+-----------+-----------------------------------------------------------------------------+
1 row in set (0.00 sec)mysql>
mysql>
mysql> insert into t_user(id,name, sex, CREATE_TIME) values(1,'lyz01', 'n', NOW());
Query OK, 1 row affected (0.10 sec)mysql> explain insert into t_user(id,name, sex, CREATE_TIME) values(2,'lyz02', 'n', NOW());
+-----------+-----------------------------------------------------------------------------+
| DATA_NODE | SQL                                                                         |
+-----------+-----------------------------------------------------------------------------+
| dn3       | insert into t_user(id,name, sex, CREATE_TIME) values(2,'lyz02', 'n', NOW()) |
+-----------+-----------------------------------------------------------------------------+
1 row in set (0.00 sec)mysql> insert into t_user(id,name, sex, CREATE_TIME) values(2,'lyz02', 'n', NOW());
Query OK, 1 row affected (0.04 sec)mysql> explain insert into t_user(id,name, sex, CREATE_TIME) values(3,'lyz03', 'n', NOW());
+-----------+-----------------------------------------------------------------------------+
| DATA_NODE | SQL                                                                         |
+-----------+-----------------------------------------------------------------------------+
| dn1       | insert into t_user(id,name, sex, CREATE_TIME) values(3,'lyz03', 'n', NOW()) |
+-----------+-----------------------------------------------------------------------------+
1 row in set (0.00 sec)mysql> insert into t_user(id,name, sex, CREATE_TIME) values(3,'lyz03', 'n', NOW());
Query OK, 1 row affected (0.01 sec)

Mycat日志如下：

08/13 21:51:45.221  DEBUG [$_NIOREACTOR-0-RW] (NonBlockingSession.java:113) -ServerConnection [id=1, schema=lyzdb, host=192.168.209.1, user=lyz,txIsolation=3, autocommit=true, schema=lyzdb]insert into t_user(id,name, sex, CREATE_TIME) values(1,'lyz01', 'n', NOW()), route={1 -> dn2{insert into t_user(id,name, sex, CREATE_TIME) values(1,'lyz01', 'n', NOW())}
} rrs insert into t_user(id,name, sex, CREATE_TIME) values(2,'lyz02', 'n', NOW());
08/13 21:52:53.005  DEBUG [$_NIOREACTOR-0-RW] (NonBlockingSession.java:113) -ServerConnection [id=1, schema=lyzdb, host=192.168.209.1, user=lyz,txIsolation=3, autocommit=true, schema=lyzdb]insert into t_user(id,name, sex, CREATE_TIME) values(2,'lyz02', 'n', NOW()), route={1 -> dn3{insert into t_user(id,name, sex, CREATE_TIME) values(2,'lyz02', 'n', NOW())}
} rrs insert into t_user(id,name, sex, CREATE_TIME) values(3,'lyz03', 'n', NOW());
08/13 21:54:00.546  DEBUG [$_NIOREACTOR-0-RW] (NonBlockingSession.java:113) -ServerConnection [id=1, schema=lyzdb, host=192.168.209.1, user=lyz,txIsolation=3, autocommit=true, schema=lyzdb]insert into t_user(id,name, sex, CREATE_TIME) values(3,'lyz03', 'n', NOW()), route={1 -> dn1{insert into t_user(id,name, sex, CREATE_TIME) values(3,'lyz03', 'n', NOW())}
} rrs

由此可见，录入数据时，Mycat根据id进行十进制求模运算，将运算结果作为路由结果，将SQL路由到指定的数据分片节点，符合我们配置的分片规则。

3、指定数据分片字段查询

08/13 21:51:45.221  DEBUG [$_NIOREACTOR-0-RW] (NonBlockingSession.java:113) -ServerConnection [id=1, schema=lyzdb, host=192.168.209.1, user=lyz,txIsolation=3, autocommit=true, schema=lyzdb]insert into t_user(id,name, sex, CREATE_TIME) values(1,'lyz01', 'n', NOW()), route={1 -> dn2{insert into t_user(id,name, sex, CREATE_TIME) values(1,'lyz01', 'n', NOW())}
} rrs insert into t_user(id,name, sex, CREATE_TIME) values(2,'lyz02', 'n', NOW());
08/13 21:52:53.005  DEBUG [$_NIOREACTOR-0-RW] (NonBlockingSession.java:113) -ServerConnection [id=1, schema=lyzdb, host=192.168.209.1, user=lyz,txIsolation=3, autocommit=true, schema=lyzdb]insert into t_user(id,name, sex, CREATE_TIME) values(2,'lyz02', 'n', NOW()), route={1 -> dn3{insert into t_user(id,name, sex, CREATE_TIME) values(2,'lyz02', 'n', NOW())}
} rrs insert into t_user(id,name, sex, CREATE_TIME) values(3,'lyz03', 'n', NOW());
08/13 21:54:00.546  DEBUG [$_NIOREACTOR-0-RW] (NonBlockingSession.java:113) -ServerConnection [id=1, schema=lyzdb, host=192.168.209.1, user=lyz,txIsolation=3, autocommit=true, schema=lyzdb]insert into t_user(id,name, sex, CREATE_TIME) values(3,'lyz03', 'n', NOW()), route={1 -> dn1{insert into t_user(id,name, sex, CREATE_TIME) values(3,'lyz03', 'n', NOW())}
} rrs

Mycat日志如下：

08/13 21:55:57.257  DEBUG [$_NIOREACTOR-0-RW] (NonBlockingSession.java:113) -ServerConnection [id=1, schema=lyzdb, host=192.168.209.1, user=lyz,txIsolation=3, autocommit=true, schema=lyzdb]select * from t_user where id = 1, route={1 -> dn2{select * from t_user where id = 1}
} rr

由此可见，执行简单的查询，如果指定分片字段，则走分片查询单个分片节点。

4、按照分片字段范围查询

mysql> explain select * from t_user where id >=3;
+-----------+----------------------------------------------+
| DATA_NODE | SQL                                          |
+-----------+----------------------------------------------+
| dn1       | SELECT * FROM t_user WHERE id >= 3 LIMIT 100 |
| dn2       | SELECT * FROM t_user WHERE id >= 3 LIMIT 100 |
| dn3       | SELECT * FROM t_user WHERE id >= 3 LIMIT 100 |
+-----------+----------------------------------------------+
3 rows in set (0.02 sec)mysql> select * from t_user where id >=3;
+----+-------+------+---------------------+
| ID | name  | sex  | CREATE_TIME         |
+----+-------+------+---------------------+
|  3 | lyz03 | n    | 2017-08-13 21:54:00 |
+----+-------+------+---------------------+
1 row in set (0.04 sec)

Mycat日志如下：

08/13 21:58:08.598  DEBUG [$_NIOREACTOR-0-RW] (NonBlockingSession.java:113) -ServerConnection [id=1, schema=lyzdb, host=192.168.209.1, user=lyz,txIsolation=3, autocommit=true, schema=lyzdb]select * from t_user where id >=3, route={1 -> dn1{SELECT *
FROM t_user
WHERE id >= 3
LIMIT 100}2 -> dn2{SELECT *
FROM t_user
WHERE id >= 3
LIMIT 100}3 -> dn3{SELECT *
FROM t_user
WHERE id >= 3
LIMIT 100}
} rrs

由此可见，如果分片字段范围的查询，则走所有节点去检索，哪怕只有一条数据在一个分片上，route路由也是走所有的分片进行检索查询。

5、按照非分片字段查询

mysql> explain select * from t_user where name = 'lyz01';
+-----------+-----------------------------------------------------+
| DATA_NODE | SQL                                                 |
+-----------+-----------------------------------------------------+
| dn1       | SELECT * FROM t_user WHERE name = 'lyz01' LIMIT 100 |
| dn2       | SELECT * FROM t_user WHERE name = 'lyz01' LIMIT 100 |
| dn3       | SELECT * FROM t_user WHERE name = 'lyz01' LIMIT 100 |
+-----------+-----------------------------------------------------+
3 rows in set (0.00 sec)mysql>
mysql> select * from t_user where name = 'lyz01';
+----+-------+------+---------------------+
| ID | name  | sex  | CREATE_TIME         |
+----+-------+------+---------------------+
|  1 | lyz01 | n    | 2017-08-13 21:51:45 |
+----+-------+------+---------------------+
1 row in set (0.01 sec)

Mycat日志如下：

08/13 21:59:01.166  DEBUG [$_NIOREACTOR-0-RW] (NonBlockingSession.java:113) -ServerConnection [id=1, schema=lyzdb, host=192.168.209.1, user=lyz,txIsolation=3, autocommit=true, schema=lyzdb]select * from t_user where name = 'lyz01', route={1 -> dn1{SELECT *
FROM t_user
WHERE name = 'lyz01'
LIMIT 100}2 -> dn2{SELECT *
FROM t_user
WHERE name = 'lyz01'
LIMIT 100}3 -> dn3{SELECT *
FROM t_user
WHERE name = 'lyz01'
LIMIT 100}
} rrs

由此可见，如果不走分片字段的查询，即使是单个数据，也要route路由所有的分片，走所有的分片进行查询。