Mysql 实现数据库读写分离

Amoeba+Mysql实现数据库读写分离

一、Amoeba 是什么

Amoeba(变形虫)项目，专注分布式数据库 proxy 开发。座落与Client、DB Server(s)之间。对客户端透明。具有负载均衡、高可用性、sql过滤、读写分离、可路由相关的query到目标数据库、可并发请求多台数据库合并结果。

主要解决：

• 降低数据切分带来的复杂多数据库结构

• 提供切分规则并降低数据切分规则给应用带来的影响

• 降低db 与客户端的连接数

• 读写分离

二、为什么要用Amoeba

目前要实现mysql的主从读写分离，主要有以下几种方案：

1、通过程序实现，网上很多现成的代码，比较复杂，如果添加从服务器要更改多台服务器的代码。

2、通过mysql-proxy来实现，由于mysql-proxy的主从读写分离是通过lua脚本来实现，目前lua的脚本的开发跟不上节奏，而写没有完美的现成的脚本，因此导致用于生产环境的话风险比较大，据网上很多人说mysql-proxy的性能不高。

3、自己开发接口实现，这种方案门槛高，开发成本高，不是一般的小公司能承担得起。

4、利用阿里巴巴的开源项目Amoeba来实现，具有负载均衡、高可用性、sql过滤、读写分离、可路由相关的query到目标数据库，并且安装配置非常简单。国产的开源软件，应该支持，目前正在使用，不发表太多结论，一切等测试完再发表结论吧，哈哈！

三、Amoeba+Mysql实现数据库读写分离

基本的原理：让“主”数据库处理事务增，删，改（INSERT，UPDATA，DELETE），“从”数据库处理SELECT查询操作。数据库复制被用来把事务性操作导致变更同步到集群中的从数据库

先介绍下部署环境：

amoeba（代理服务器）:192.168.220.33

master-mysql：192.168.220.30

slave1-mysql：192.168.220.31

slave2-mysql：192.168.220.32

客户机（本机 win11）：192.168.220.2

系统：centOS 7.9

MySQL：5.7

Amoeba：3.0.5 （框架是居于java语言开发）

jdk：1.8

部署MySQL一主多从：

注：做主从数据库里数据最好是保持一致

1、主数据库：master-mysql

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)

mysql> 
mysql> grant all on *.* to 'test'@'192.168.220.%' identified by '1234.Com'; #创建授权用户 为amoeba提供登录
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> 
mysql> grant replication slave on *.* to 'slave'@'192.168.220.%' identified by '1234.Com'; #主从模式
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql>
mysql> show master status\G;
*************************** 1. row ***************************
             File: mysql-bin.000001 #从库加入主库时 需要配置的二进制文件名
         Position: 154 　　　　　　　 # 二进制日子 从 pos 154 开始被slave
复制
备份 Binlog_Do_DB: Binlog_Ignore_DB: Executed_Gtid_Set: 1 row in set (0.00 sec) ERROR: No query specified mysql>

2、从数据库：slave1-mysql

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)

mysql> 
mysql> change master to master_host='192.168.220.30',master_user='slave',master_password='1234.Com',,master_log_file='mysql-bin.000001',master_log_pos=154；
Query OK, 0 rows affected, 2 warnings (0.01 sec)

mysql> 
mysql> start slave;
Query OK, 0 rows affected (0.01 sec)

mysql> show slave status\G; #查看从库的连接状态，I/O，SQL 都要为 YES
*************************** 1. row ***************************
               Slave_IO_State: Connecting to master
                  Master_Host: 192.168.220.30
                  Master_User: slave
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000001
          Read_Master_Log_Pos: 154
               Relay_Log_File: slave1-relay-bin.000001
                Relay_Log_Pos: 4
        Relay_Master_Log_File: mysql-bin.000001
             Slave_IO_Running: YES 
            Slave_SQL_Running: Yes
              Replicate_Do_DB: 

       ····················

ERROR: 
No query specified

mysql> grant all on *.* to 'test'@'192.168.220.%' identified by '1234.Com'; #创建授权用户 为amoeba提供登录
Query OK, 0 rows affected, 1 warning (0.00 sec)

3、从数据库：slave2-mysql

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)



mysql> 
mysql> change master to master_host='192.168.220.30',master_user='slave',master_password='1234.Com',,master_log_file='mysql-bin.000001',master_log_pos=154；
Query OK, 0 rows affected, 2 warnings (0.01 sec)

mysql> 
mysql> start slave;
Query OK, 0 rows affected (0.01 sec)

mysql> show slave status\G; #查看从库的连接状态，I/O，SQL 都要为 YES
*************************** 1. row ***************************
               Slave_IO_State: Connecting to master
                  Master_Host: 192.168.220.30
                  Master_User: slave
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000001
          Read_Master_Log_Pos: 154
               Relay_Log_File: slave1-relay-bin.000001
                Relay_Log_Pos: 4
        Relay_Master_Log_File: mysql-bin.000001
             Slave_IO_Running: YES 
            Slave_SQL_Running: Yes
              Replicate_Do_DB: 

       ····················

ERROR: 
No query specified

mysql> grant all on *.* to 'test'@'192.168.220.%' identified by '1234.Com'; #创建授权用户 为amoeba提供登录
Query OK, 0 rows affected, 1 warning (0.00 sec)

4、主库测试：创建一个测试库并添加创建表和添加数据，查看从库是否同步

mysql> create database test; 
Query OK, 1 row affected (0.00 sec)

mysql> use test;
Database changed

mysql> create table test (id int);
Query OK, 0 rows affected (0.01 sec)

mysql> insert into test values (1);
Query OK, 1 row affected (0.00 sec)

mysql> select * from test;
+------+
| id   |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

mysql>

5、slave1 从库测试：

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
+--------------------+
5 rows in set (0.00 sec)

mysql> select * from test.test;
+------+
| id   |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

mysql>

6、slave2 从库测试：

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
+--------------------+
5 rows in set (0.00 sec)

mysql> select * from test.test;
+------+
| id   |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

mysql>

从数据库同步正常，主从数据库部署完成，接下来部署 Amoeba

Amoeba 安装部署

1、安装java环境

先去官网下载：http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html

安装

[root@amoeba src]# rpm -ivh jdk-8u111-linux-x64.rpm
Preparing...                ########################################### [100%]
   1:jdk1.8.0_111           ########################################### [100%]
Unpacking JAR files...
    tools.jar...
    plugin.jar...
    javaws.jar...
    deploy.jar...
    rt.jar...
    jsse.jar...
    charsets.jar...
    localedata.jar...

设置Java环境

[root@amoeba src]# vim /etc/profile

#set java environment
JAVA_HOME=/usr/java/jdk1.8.0_111
JRE_HOME=/usr/java/jdk1.8.0_111/jre
CLASS_PATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar:$JRE_HOME/lib
PATH=$PATH:$JAVA_HOME/bin:$JRE_HOME/bin
export JAVA_HOME JRE_HOME CLASS_PATH PATH[root@bogon amoeba]# source /etc/profile

测试是否安装成功

[root@bogon src]# java -version
java version "1.8.0_111"
Java(TM) SE Runtime Environment (build 1.8.0_111-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.111-b14, mixed mode)

2、安装Amoeba

可以从https://sourceforge.net/projects/amoeba/files/Amoeba%20for%20mysql/3.x/下载最新版本的Amoeba，我这里下载的是amoeba-mysql-3.0.5-RC-distribution.zip。Amoeba安装非常简单，直接解压即可使用，这里将Amoeba解压到/usr/local/amoeba目录下，这样就安装完成了

[root@amoeba amoeba]# pwd
/usr/local/amoeba
[root@amoeba amoeba]# ll
total 48
drwxr-xr-x 2 root root    63 Aug 16 10:24 benchmark
drwxr-xr-x 2 root root   131 Feb 29  2012 bin
-rwxr-xr-x 1 root root  3976 Aug 29  2012 changelogs.txt
drwxr-xr-x 2 root root   243 Aug 16 14:53 conf
drwxr-xr-x 3 root root  4096 Aug 16 10:24 lib
-rwxr-xr-x 1 root root 34520 Aug 29  2012 LICENSE.txt
drwxr-xr-x 2 root root   133 Aug 16 10:25 logs
-rwxr-xr-x 1 root root  2031 Aug 29  2012 README.html
[root@amoeba amoeba]#

3.配置Amoeba（实现读写分离，两个slave“读”负载）

Amoeba的配置文件在本环境下位于：/usr/local/amoeba/conf 目录下，实现读写分离和负载只需要 dbServers.xml和amoeba.xml 两个文件即可，下面介绍

dbServer.xml

[root@amoeba amoeba]# cd conf/
[root@amoeba conf]# ls
access_list.conf  amoeba.xml    dbServers.xml  functionMap.xml  log4j.xml  ruleFunctionMap.xml
amoeba.dtd        dbserver.dtd  function.dtd   log4j.dtd        rule.dtd   rule.xml
[root@amoeba conf]# cat dbServers.xml 
<?xml version="1.0" encoding="gbk"?>

<!DOCTYPE amoeba:dbServers SYSTEM "dbserver.dtd">
<amoeba:dbServers xmlns:amoeba="http://amoeba.meidusa.com/">

        <!-- 
            Each dbServer needs to be configured into a Pool,
            If you need to configure multiple dbServer with load balancing that can be simplified by the following configuration:
             add attribute with name virtual = "true" in dbServer, but the configuration does not allow the element with name factoryConfig
             such as 'multiPool' dbServer   
        -->
        
    <dbServer name="abstractServer" abstractive="true">
        <factoryConfig class="com.meidusa.amoeba.mysql.net.MysqlServerConnectionFactory">
            <property name="manager">${defaultManager}</property>
            <property name="sendBufferSize">64</property>
            <property name="receiveBufferSize">128</property>
                
            <!-- mysql port -->
            <property name="port">3306</property>  #设置Amoeba 连接数据库的端口，默认 3306
            
            <!-- mysql schema -->
            <property name="schema">mysql</property>  #设置 缺省的数据库，我这里使用的MySQL版本为5.7版本，默认是没有test库的，会报所以找不到默认的库，我之前搭建的MySQL版本是5.5是不需要修改的，没注意到这一点
            
            <!-- mysql user -->
            <property name="user">test</property>  #设置amoeba连接后端数据库服务器的账号和密码，上面已为 test 授权 和设置了密码
            
            <!--  mysql password -->
            <property name="password">1234.Com</property>

        </factoryConfig>

        <poolConfig class="com.meidusa.amoeba.net.poolable.PoolableObjectPool">
            <property name="maxActive">500</property>  #最大连接数，默认为500
            <property name="maxIdle">500</property>　　#最大空闲连接数
            <property name="minIdle">10</property>　　#最新空闲连接数
            <property name="minEvictableIdleTimeMillis">600000</property>
            <property name="timeBetweenEvictionRunsMillis">600000</property>
            <property name="testOnBorrow">true</property>
            <property name="testOnReturn">true</property>
            <property name="testWhileIdle">true</property>
        </poolConfig>
    </dbServer>

    <dbServer name="master"  parent="abstractServer">  #设置一个空间名称，可任意命名，这里定义为：master，顾名思义就是为master库创建一个命名空间，后面会用到
        <factoryConfig>
            <!-- mysql ip -->
            <property name="ipAddress">192.168.220.30</property> #设置 master的IP，功能可写
        </factoryConfig>
    </dbServer>
    
    <dbServer name="slave1"  parent="abstractServer">  #设置slava1 命名空间名称
        <factoryConfig>
            <!-- mysql ip -->
            <property name="ipAddress">192.168.220.31</property> # 设置slave1的IP，功能可写
        </factoryConfig>
    </dbServer>
    <dbServer name="slave2"  parent="abstractServer"> #设置slava2 命名空间名称
        <factoryConfig>
            <!-- mysql ip -->
            <property name="ipAddress">192.168.220.32</property>  #设置 slave的ip，功能可写
        </factoryConfig>
    </dbServer>
    
    <dbServer name="slaves" virtual="true">  #设置定义一个虚拟的dbserver，实际上相当于一个dbserver组，这里将可读的数据库ip统一放到一个组中，将这个组的名字命名为slaves
        <poolConfig class="com.meidusa.amoeba.server.MultipleServerPool">
            <!-- Load balancing strategy: 1=ROUNDROBIN , 2=WEIGHTBASED , 3=HA-->
            <property name="loadbalance">1</property> #选择调度算法，1表示复制均衡，2表示权重，3表示HA， 这里选择1
            
            <!-- Separated by commas,such as: server1,server2,server1 -->
            <property name="poolNames">slave1,slave2</property>  #slave组成员，把slave1，slave2 加入成员里，可实现 “读” 负载
        </poolConfig>
    </dbServer>
        
</amoeba:dbServers>
[root@amoeba conf]#

amoeba.xml

[root@amoeba amoeba]# cd conf/
[root@amoeba conf]# ls
access_list.conf  amoeba.xml    dbServers.xml  functionMap.xml  log4j.xml  ruleFunctionMap.xml
amoeba.dtd        dbserver.dtd  function.dtd   log4j.dtd        rule.dtd   rule.xml
[root@amoeba conf]# cat amoeba.xml 
<?xml version="1.0" encoding="gbk"?>

<!DOCTYPE amoeba:configuration SYSTEM "amoeba.dtd">
<amoeba:configuration xmlns:amoeba="http://amoeba.meidusa.com/">

    <proxy>
    
        <!-- service class must implements com.meidusa.amoeba.service.Service -->
        <service name="Amoeba for Mysql" class="com.meidusa.amoeba.net.ServerableConnectionManager">
            <!-- port -->
            <property name="port">8066</property>  #设置amoeba 今天的端口，默认是8066
            
            <!-- bind ipAddress -->
            <!-- 
            <property name="ipAddress">127.0.0.1</property>
             -->
            
            <property name="manager">${clientConnectioneManager}</property>
            
            <property name="connectionFactory">
                <bean class="com.meidusa.amoeba.mysql.net.MysqlClientConnectionFactory">
                    <property name="sendBufferSize">128</property>
                    <property name="receiveBufferSize">64</property>
                </bean>
            </property>
            
            <property name="authenticator">
                <bean class="com.meidusa.amoeba.mysql.server.MysqlClientAuthenticator">
                    
                    <property name="user">amoeba</property>  #提供客服端连接amoeba是需要使用设定的账号，账号密码可任意设置和数据服务器里的密码无关
                    
                    <property name="password">123456</property>
                    
                    <property name="filter">
                        <bean class="com.meidusa.amoeba.server.IPAccessController">
                            <property name="ipFile">${amoeba.home}/conf/access_list.conf</property>
                        </bean>
                    </property>
                </bean>
            </property>
            
        </service>
        
        <!-- server class must implements com.meidusa.amoeba.service.Service -->
        <service name="Amoeba Monitor Server" class="com.meidusa.amoeba.monitor.MonitorServer">
            <!-- port -->
            <!--  default value: random number
            <property name="port">9066</property>
            -->
            <!-- bind ipAddress -->
            <property name="ipAddress">127.0.0.1</property>
            <property name="daemon">true</property>
            <property name="manager">${clientConnectioneManager}</property>
            <property name="connectionFactory">
                <bean class="com.meidusa.amoeba.monitor.net.MonitorClientConnectionFactory"></bean>
            </property>
            
        </service>
        
        <runtime class="com.meidusa.amoeba.mysql.context.MysqlRuntimeContext">
            <!-- proxy server net IO Read thread size -->
            <property name="readThreadPoolSize">20</property>
            
            <!-- proxy server client process thread size -->
            <property name="clientSideThreadPoolSize">30</property>
            
            <!-- mysql server data packet process thread size -->
            <property name="serverSideThreadPoolSize">30</property>
            
            <!-- per connection cache prepared statement size  -->
            <property name="statementCacheSize">500</property>
            
            <!-- query timeout( default: 60 second , TimeUnit:second) -->
            <property name="queryTimeout">60</property>
        </runtime>
        
    </proxy>
    
    <!-- 
        Each ConnectionManager will start as thread
        manager responsible for the Connection IO read , Death Detection
    -->
    <connectionManagerList>
        <connectionManager name="clientConnectioneManager" class="com.meidusa.amoeba.net.MultiConnectionManagerWrapper">
            <property name="subManagerClassName">com.meidusa.amoeba.net.ConnectionManager</property>
            <!-- 
              default value is avaliable Processors 
            <property name="processors">5</property>
             -->
        </connectionManager>
        <connectionManager name="defaultManager" class="com.meidusa.amoeba.net.MultiConnectionManagerWrapper">
            <property name="subManagerClassName">com.meidusa.amoeba.net.AuthingableConnectionManager</property>
            
            <!-- 
              default value is avaliable Processors 
            <property name="processors">5</property>
             -->
        </connectionManager>
    </connectionManagerList>
    
        <!-- default using file loader -->
    <dbServerLoader class="com.meidusa.amoeba.context.DBServerConfigFileLoader">
        <property name="configFile">${amoeba.home}/conf/dbServers.xml</property>
    </dbServerLoader>
    
    <queryRouter class="com.meidusa.amoeba.mysql.parser.MysqlQueryRouter">
        <property name="ruleLoader">
            <bean class="com.meidusa.amoeba.route.TableRuleFileLoader">
                <property name="ruleFile">${amoeba.home}/conf/rule.xml</property>
                <property name="functionFile">${amoeba.home}/conf/ruleFunctionMap.xml</property>
            </bean>
        </property>
        <property name="sqlFunctionFile">${amoeba.home}/conf/functionMap.xml</property>
        <property name="LRUMapSize">1500</property>
        <property name="defaultPool">master</property>  #设置amoeba默认是的池，这里设置为master（在dbServers.xml文件中，我们定义了一会master的空间名称以及对应的服务器IP）
        
        <property name="writePool">master</property>  #设置写的池，master作为主数据库，处理的业务为 增，删，改 都是写操作，所以这设置为master
        <property name="readPool">slaves</property>   #设置读的池  slave 作为从库，负责 查（SELECT，因为我们有两个slave，在定义命名空间时，我们配置了一个slaves组，里面有slave1，slave2两个成员，这样就可以达到 读的负载
        <property name="needParse">true</property>

    </queryRouter>
</amoeba:configuration>

3、启动Amoeba

[root@amoeba ~]# /usr/local/amoeba/bin/launcher &
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchStandard(Launcher.java:329)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:239)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:409)
    at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:127)
    at org.codehaus.classworlds.Launcher.main(Launcher.java:110)
Caused by: com.meidusa.toolkit.common.bean.util.InitialisationException: default pool required!,defaultPool=writedb invalid
    at com.meidusa.amoeba.route.AbstractQueryRouter.init(AbstractQueryRouter.java:469)
    at com.meidusa.amoeba.context.ProxyRuntimeContext.initAllInitialisableBeans(ProxyRuntimeContext.java:337)
    ... 11 more
 2022-8-16 18:46:37 [INFO] Project Name=Amoeba-MySQL, PID=1577 , System shutdown ....
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option PermSize=16m; support was removed in 8.0
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=96m; support was removed in 8.0
2022-8-16 18:50:19 [INFO] Project Name=Amoeba-MySQL, PID=1602 , starting...
log4j:WARN log4j config load completed from file:/usr/local/amoeba/conf/log4j.xml
2022-8-16 18:50:21,668 INFO  context.MysqlRuntimeContext - Amoeba for Mysql current versoin=5.1.45-mysql-amoeba-proxy-3.0.4-BETA
log4j:WARN ip access config load completed from file:/usr/local/amoeba/conf/access_list.conf
2022-8-16 18:50:22,852 INFO  net.ServerableConnectionManager - Server listening on 0.0.0.0/0.0.0.0:8066.

查看端口

[root@amoeba ~]# netstat -anpt | grep java
tcp6       0      0 127.0.0.1:13319         :::*                    LISTEN      21350/java          
tcp6       0      0 :::8066                 :::*                    LISTEN      21350/java

4、Amoeba 登录测试（客户端-本机：win11）

测试结果：登录后所在的库是“mysql”库，可读取，可写入，到这里数据库读写分离部，负载部署完成！！！

　　　下面就是读写分离的效果测试：

四、测试读写分离，负载效果

1、读写分离测试：

　　测试1 ：mysql-master down机，写入报错，读正常

mysql-master：

[root@mysql_master ~]# systemctl stop mysqld

客服端：

mysql> select * from test;  #可正常查询
+------+
| id   |
+------+
|    1 |
|    2 |
+------+
2 rows in set (0.00 sec)

mysql>
mysql> insert into test values (3);  
ERROR 2013 (HY000): Lost connection to MySQL server during query  #写入失败

　　测试2 ：关闭两台slave，读取失败，插入成功

mysql-master

[root@mysql_master ~]# systemctl start mysqld

mysql-slave1

[root@slave1 ~]# systemctl stop mysqld

mysql-slave2

[root@slave2 ~]# systemctl stop mysqld

客服端：

mysql> insert into test values (3);
Query OK, 1 row affected (0.00 sec)

mysql> select * from test;
ERROR 2013 (HY000): Lost connection to MySQL server during query  #查询失败
mysql>

　　测试3：开启slava1，save2上的mysql，查看数据是否自动同步

mysql-slave1

[root@slave1 ~]# systemctl start mysqld

mysql-slave2

[root@slave2 ~]# systemctl start mysqld

客服端：

mysql> select * from test;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
+------+
4 rows in set (0.00 sec)

mysql>
mysql> insert into test values (4);
Query OK, 1 row affected (0.00 sec)

mysql> select * from test;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
+------+
5 rows in set (0.00 sec)

mysql>

读写分离测试完毕！！！

2、slave “读” 负载测试：

mysql-slave1：在test表插入值：100

[root@slave1 ~]# mysql -uroot -p
Enter password:
mysql>
mysql> select * from test;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
+------+
4 rows in set (0.00 sec)

mysql> insert into test values (100);
Query OK, 1 row affected (0.00 sec)

mysql> select * from test;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|  100 |
+------+
5 rows in set (0.00 sec)

mysql>

mysql-slave2：在test表插入值：200

[root@slave2 ~]# mysql -uroot -p
Enter password:
mysql>
mysql> select * from test;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
+------+
4 rows in set (0.00 sec)

mysql> insert into test values (200);
Query OK, 1 row affected (0.00 sec)

mysql> select * from test;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|  200 |
+------+
5 rows in set (0.00 sec)

mysql>

客服端：

mysql> select * from test;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|  200 |
+------+
5 rows in set (0.00 sec)

mysql> select * from test;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|  100 |
+------+
5 rows in set (0.00 sec)

mysql> select * from test;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|  200 |
+------+
5 rows in set (0.00 sec)

mysql> select * from test;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|  100 |
+------+
5 rows in set (0.00 sec)

mysql>