mycat是什么？你是怎么理解的？你们公司分库分表的分片规则是什么？搭建mycat环境常用的配置文件有哪些？

1、mycat是什么？

国内最活跃的、性能最好的开源数据库分库分表中间件

• 一个彻底开源的，面向企业应用开发的大数据库集群
• 支持事务、ACID、可以替代MySQL的加强版数据库
• 一个可以视为MySQL集群的企业级数据库，用来替代昂贵的Oracle集群
• 一个融合内存缓存技术、NoSQL技术、HDFS大数据的新型SQL Server
• 结合传统数据库和新型分布式数据仓库的新一代企业级数据库产品
• 一个新颖的数据库中间件产品

2、分片规则：取模

<tableRule name="mod-long">

    <rule>

        <columns>user_id</columns>

        <algorithm>mod-long</algorithm>

    </rule>

</tableRule>

<function name="mod-long" class="io.mycat.route.function.PartitionByMod">

    <!-- how many data nodes -->

    <property name="count">3</property>

</function>

配置说明：
| 标签属性 | 说明 |
| --------- | -------------------- |
| columns | 标识将要分片的表字段 |
| algorithm | 分片函数 |
| count | 分片数量 |

根据 id 进行十进制求模预算。

3、搭建mycat环境常用的配置文件

rule.xml：

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE mycat:rule SYSTEM "rule.dtd">

<mycat:rule xmlns:mycat="http://io.mycat/">

     <tableRule name="auto-sharding-rang-mod-order">

    <rule>

        <columns>id</columns>

        <algorithm>rang-mod-dm</algorithm>

    </rule>

</tableRule>

<function name="rang-mod-dm"  class="io.mycat.route.function.PartitionByMod">

    <property name="count">3</property>

</function>

</mycat:rule>

schema.xml：

<?xml version="1.0"?>

<!DOCTYPE mycat:schema SYSTEM "schema.dtd">

<mycat:schema xmlns:mycat="http://io.mycat/">

    <schema name="dm_order"  checkSQLschema="true" sqlMaxLimit="100">

       <table name="dm_order" primaryKey="id" autoIncrement="true" dataNode="dn1,dn2,dn3"

        rule="auto-sharding-rang-mod-order"/>

    </schema>

    <dataNode name="dn1"   dataHost="a"  database="dm_order1"/>

<dataNode name="dn2"   dataHost="a"  database="dm_order2"/>

<dataNode name="dn3"   dataHost="a"  database="dm_order3"/>

<dataHost  name="a"   maxCon="1000"  minCon="10"  balance="0"

    writeType="0"   dbType="mysql"

        dbDriver="native" switchType="1"  slaveThreshold="100">

    <heartbeat>select 1</heartbeat>

    <writeHost host="hostM1"

        url="192.168.133.130:3306" user="root" password="123456">

    </writeHost>

</dataHost>

</mycat:schema>

server.xml：

<?xml version="1.0" encoding="UTF-8"?>

<!-- - - Licensed under the Apache License, Version 2.0 (the "License");

    - you may not use this file except in compliance with the License. - You

    may obtain a copy of the License at - - http://www.apache.org/licenses/LICENSE-2.0

    - - Unless required by applicable law or agreed to in writing, software -

    distributed under the License is distributed on an "AS IS" BASIS, - WITHOUT

    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. - See the

    License for the specific language governing permissions and - limitations

    under the License. -->

<!DOCTYPE mycat:server SYSTEM "server.dtd">

<mycat:server xmlns:mycat="http://io.mycat/">

    <system>

    <property name="useSqlStat">0</property>  <!-- 1为开启实时统计、0为关闭 -->

    <property name="useGlobleTableCheck">0</property>  <!-- 1为开启全加班一致性检测、0为关闭 -->

        <property name="sequnceHandlerType">2</property>

      <!--  <property name="useCompression">1</property>--> <!--1为开启mysql压缩协议-->

        <!--  <property name="fakeMySQLVersion">5.6.20</property>--> <!--设置模拟的MySQL版本号-->

    <!-- <property name="processorBufferChunk">40960</property> -->

    <!--

    <property name="processors">1</property>

    <property name="processorExecutor">32</property>

     -->

        <!--默认为type 0: DirectByteBufferPool | type 1 ByteBufferArena-->

        <property name="processorBufferPoolType">0</property>

        <!--默认是65535 64K 用于sql解析时最大文本长度 -->

        <!--<property name="maxStringLiteralLength">65535</property>-->

        <!--<property name="sequnceHandlerType">0</property>-->

        <!--<property name="backSocketNoDelay">1</property>-->

        <!--<property name="frontSocketNoDelay">1</property>-->

        <!--<property name="processorExecutor">16</property>-->

        <!--

            <property name="serverPort">8066</property> <property name="managerPort">9066</property>

            <property name="idleTimeout">300000</property> <property name="bindIp">0.0.0.0</property>

            <property name="frontWriteQueueSize">4096</property> <property name="processors">32</property> -->

        <!--分布式事务开关，0为不过滤分布式事务，1为过滤分布式事务（如果分布式事务内只涉及全局表，则不过滤），2为不过滤分布式事务,但是记录分布式事务日志-->

        <property name="handleDistributedTransactions">0</property>

            <!--

            off heap for merge/order/group/limit      1开启   0关闭

        -->

        <property name="useOffHeapForMerge">1</property>

        <!--

            单位为m

        -->

        <property name="memoryPageSize">1m</property>

        <!--

            单位为k

        -->

        <property name="spillsFileBufferSize">1k</property>

        <property name="useStreamOutput">0</property>

        <!--

            单位为m

        -->

        <property name="systemReserveMemorySize">384m</property>

        <!--是否采用zookeeper协调切换  -->

        <property name="useZKSwitch">true</property>

    </system>

    <!-- 全局SQL防火墙设置 -->

    <!--

    <firewall>

       <whitehost>

          <host host="127.0.0.1" user="mycat"/>

          <host host="127.0.0.2" user="mycat"/>

       </whitehost>

       <blacklist check="false">

       </blacklist>

    </firewall>

    -->

    <user name="root">

        <property name="password">123456</property>

        <property name="schemas">dm_order</property>

        <!-- 表级 DML 权限设置 -->

        <!--

        <privileges check="false">

            <schema name="TESTDB" dml="0110" >

                <table name="tb01" dml="0000"></table>

                <table name="tb02" dml="1111"></table>

            </schema>

        </privileges>

         -->

    </user>

</mycat:server>