After the users of the website reach a certain scale , Database becomes the bottleneck of website because of the high load pressure . Fortunately, most of the current mainstream databases provide the master-slave hot standby function , By configuring the master-slave relationship of two databases , You can synchronize data updates from one database to another server . Website uses this function of database , Realize the separation of reading and writing of database , To improve database load pressure . As shown in the figure below :



   When the application server writes data , Accessing the master database , Master database synchronizes data updates to slave database through master-slave replication mechanism , So when the application server reads the data , You can get data from the database . In order to facilitate application access to the database after read-write separation , Usually, the application server uses a special database access module , Make database read-write separation transparent to application .

From 《 Technical framework of large website _ Core principles and case analysis 》

       This blog is to realize “ Special database access module ”, Make database read-write separation transparent to application . in addition ,mysql The master-slave replication of the database can refer to my
mysql5.7.18 Installation and master-slave replication of <>
. be careful , Database realizes master-slave replication , To separate the reading and writing of database , therefore , If there is no master-slave database replication, remember to implement the master-slave database replication first

Configure read and write data sources ( Master slave database )
# Master database data source jdbc.driverClassName=com.mysql.jdbc.Driver jdbc.url=jdbc:mysql://
jdbc.username=root jdbc.password=123456 jdbc.initialSize=1 jdbc.minIdle=1
jdbc.maxActive=20 jdbc.maxWait=60000 jdbc.removeAbandoned=true
jdbc.removeAbandonedTimeout=180 jdbc.timeBetweenEvictionRunsMillis=60000
jdbc.minEvictableIdleTimeMillis=300000 jdbc.validationQuery=SELECT 1
jdbc.testWhileIdle=true jdbc.testOnBorrow=false jdbc.testOnReturn=false
# From database data source slave.jdbc.driverClassName=com.mysql.jdbc.Driver slave.jdbc.url
slave.jdbc.username=root slave.jdbc.password=123456 slave.jdbc.initialSize=1
slave.jdbc.minIdle=1 slave.jdbc.maxActive=20 slave.jdbc.maxWait=60000
slave.jdbc.removeAbandoned=true slave.jdbc.removeAbandonedTimeout=180
slave.jdbc.minEvictableIdleTimeMillis=300000 slave.jdbc.validationQuery=SELECT 1
slave.jdbc.testWhileIdle=true slave.jdbc.testOnBorrow=false
     main , Remember to change the database address to your own , Your account and password need to be changed to your own ; Other configuration items , You can set your own

<?xml version="1.0" encoding="UTF-8"?> <beans
xmlns="" xmlns:xsi
xmlns:context="" xmlns:aop
xmlns:tx="" xsi:schemaLocation
=" http:// http:// http:// http:// http:// http:// http://"> <!-- master data source --> <bean
id="masterDataSource"class=""> <!-- Basic properties
url,user,password --> <property name="driverClassName"
value="${jdbc.driverClassName}" /> <property name="url" value="${jdbc.url}" />
<property name="username" value="${jdbc.username}" /> <property name="password"
value="${jdbc.password}" /> <property name="initialSize"
value="${jdbc.initialSize}" /> <property name="minIdle" value="${jdbc.minIdle}"
/> <property name="maxActive" value="${jdbc.maxActive}" /> <property
name="maxWait" value="${jdbc.maxWait}" /> <!-- Whether to recycle beyond the time limit --> <property
name="removeAbandoned" value="${jdbc.removeAbandoned}" /> <!-- How long does it exceed the time limit ; -->
<property name="removeAbandonedTimeout" value="${jdbc.removeAbandonedTimeout}"
/> <!-- How often is the configuration interval checked , Detect idle connections that need to be closed , In milliseconds --> <property
value="${jdbc.timeBetweenEvictionRunsMillis}" /> <!-- Configure the minimum lifetime of a connection in the pool , In milliseconds
--> <property name="minEvictableIdleTimeMillis"
value="${jdbc.minEvictableIdleTimeMillis}" /> <!-- Used to check whether the connection is valid sql, Request is a query statement -->
<property name="validationQuery" value="${jdbc.validationQuery}" /> <!--
Detect when applying for connection --> <property name="testWhileIdle" value="${jdbc.testWhileIdle}" />
<!-- Execute on connection request validationQuery Check if the connection is valid , Configured as true Will degrade performance --> <property
name="testOnBorrow" value="${jdbc.testOnBorrow}" /> <!--
Execute on return connection validationQuery Check if the connection is valid , Configured as true Will degrade performance --> <property name="testOnReturn"
value="${jdbc.testOnReturn}" /> </bean> <!-- slave data source --> <bean
id="slaveDataSource"class=""> <property
name="driverClassName" value="${slave.jdbc.driverClassName}" /> <property
name="url" value="${slave.jdbc.url}" /> <property name="username"
value="${slave.jdbc.username}" /> <property name="password"
value="${slave.jdbc.password}" /> <property name="initialSize"
value="${slave.jdbc.initialSize}" /> <property name="minIdle"
value="${slave.jdbc.minIdle}" /> <property name="maxActive"
value="${slave.jdbc.maxActive}" /> <property name="maxWait"
value="${slave.jdbc.maxWait}" /> <property name="removeAbandoned"
value="${slave.jdbc.removeAbandoned}" /> <property
name="removeAbandonedTimeout" value="${slave.jdbc.removeAbandonedTimeout}" />
<property name="timeBetweenEvictionRunsMillis"
value="${slave.jdbc.timeBetweenEvictionRunsMillis}" /> <property
value="${slave.jdbc.minEvictableIdleTimeMillis}" /> <property
name="validationQuery" value="${slave.jdbc.validationQuery}" /> <property
name="testWhileIdle" value="${slave.jdbc.testWhileIdle}" /> <property
name="testOnBorrow" value="${slave.jdbc.testOnBorrow}" /> <property
name="testOnReturn" value="${slave.jdbc.testOnReturn}" /> </bean> <!--
Dynamic data source , according to service The annotation on the interface determines which data source to take --> <bean id="dataSource"class
="com.yzb.util.DynamicDataSource"> <property name="targetDataSources"> <map
key-type="java.lang.String"> <!-- write or slave --> <entry key="slave"
value-ref="slaveDataSource"/> <!-- read or master --> <entry key="master"
value-ref="masterDataSource"/> </map> </property> <property
name="defaultTargetDataSource" ref="masterDataSource"/> </bean> <!-- Mybatis file
--> <bean id="sqlSessionFactory"class
="org.mybatis.spring.SqlSessionFactoryBean"> <property name="configLocation"
value="classpath:mybatis-config.xml" /> <property name="dataSource"
ref="dataSource" /> <!-- Map file path --> <property name="mapperLocations"
value="classpath*:dbmappers/*.xml" /> </bean> <beanclass
="org.mybatis.spring.mapper.MapperScannerConfigurer"> <property
name="basePackage" value="com.yzb.dao" /> <property
name="sqlSessionFactoryBeanName" value="sqlSessionFactory" /> </bean> <!--
Transaction manager --> <bean id="transactionManager"class
="org.springframework.jdbc.datasource.DataSourceTransactionManager"> <property
name="dataSource" ref="dataSource" /> </bean> <!-- Declarative opening -->
<tx:annotation-driven transaction-manager="transactionManager" proxy-target-
class="true" order="1"/> <!-- Method analysis for business logic layer @DataSource annotation
  For the current thread HandleDataSource Inject data source -->  <bean id="dataSourceAspect"class
="com.yzb.util.DataSourceAspect" /> <aop:config proxy-target-class="true">
<aop:aspect id="dataSourceAspect" ref="dataSourceAspect" order="2">
<aop:pointcut id="tx" expression="execution(* com.yzb.service.impl..*.*(..))
"/> <aop:before pointcut-ref="tx" method="before" /> </aop:aspect>
</aop:config> </beans>
AOP Dynamic switch of data source
package com.yzb.util; import java.lang.annotation.ElementType; import
java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target; /** * RUNTIME * The compiler will record the comments in the class file , At runtime VM
Will keep comments , So it can be read reflexively . **/ @Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)public @interface DataSource { String value(); }
package com.yzb.util; import java.lang.reflect.Method; import
org.aspectj.lang.JoinPoint;import org.aspectj.lang.reflect.MethodSignature;
public class DataSourceAspect { /** * stay dao Layer method acquisition datasource Before object , Specify the current thread data source in the slice */
public void before(JoinPoint point) { Object target = point.getTarget(); String
method= point.getSignature().getName(); Class<?>[] classz =
target.getClass().getInterfaces();// Get the interface of the target class , therefore @DataSource Need to be written on the interface Class<?>[]
parameterTypes = ((MethodSignature) point.getSignature())
.getMethod().getParameterTypes();try { Method m = classz[0].getMethod(method,
parameterTypes);if (m != null && m.isAnnotationPresent(DataSource.class)) {
DataSource data= m.getAnnotation(DataSource.class); System.out.println(
" User selects database type :" + data.value()); HandleDataSource.putDataSource(data.value()); //
Put the data source into the current thread } } catch (Exception e) { e.printStackTrace(); } } }
package com.yzb.util; import
class DynamicDataSource extends AbstractRoutingDataSource { /** * Get data source related key
this key yes Map<String,DataSource> resolvedDataSources Data source bound key value *
Passing determineTargetDataSource Use when getting the target data source */ @Override protected Object
determineCurrentLookupKey() {return HandleDataSource.getDataSource(); } }
package com.yzb.util; public class HandleDataSource { public static final
ThreadLocal<String> holder =new ThreadLocal<String>(); /** * Bind current thread data source * *
@param key */ public static void putDataSource(String datasource) {
holder.set(datasource); }/** * Get the data source of the current thread * * @return */ public static String
getDataSource() {return holder.get(); } }
service Application on interface @DataSource Implement data source specification
package com.yzb.service; import java.util.List; import com.yzb.model.Person;
import com.yzb.util.DataSource; public interface IPersonService { /** *
Load all person *@return */ List<Person> listAllPerson(); /** * Query someone's information * @param
personId *@return */ @DataSource("slave") // Specify use from data source Person getPerson(int
personId);boolean updatePerson(Person person); }
Attention points

   When testing , How to know that it's from the database ? We can modify the value of a certain field of the record queried from the database , To distinguish the main , From database ;

       Transaction needs attention , Try to keep transactions on one data source ;

       When a service More than one aop Time , Need attention aop The order of weaving , utilize order Key words control weaving order ;

   Complete project github address <>
:, Realized in the project redis cache , Don't visit :http://localhost:8080/maven-ssm-web/personController/showPerson There's no problem , Of course you can redis Build and integrate services ;

   test url:http://localhost:8080/maven-ssm-web/personController/person?personId=1

reference resources

  《 Technical framework of large website _ Core principles and case analysis 》

  Spring+MyBatis Implementation of database read-write separation scheme <>