verydapeng/spring-dynamic-schema

Demo to switch schema dynamically

We have a huge read-only MySql database which is refreshed daily.

However the refresh is not atomic, and it may occasionally fail half way.

The natural solution will be only doing the fresh on a backup schema, then swap the schema.

Sad enough, there is no easy solution to rename the schema. So we need some logic from application to handle the switch

Solution

Wrap the datasource inside a proxy!

private volatile boolean useDatasource1 = true;

@Bean
DataSource dataSource() {

    DataSource ds1 = createDatasource("db1");
    DataSource ds2 = createDatasource("db2");

    return (DataSource) Proxy.newProxyInstance(this.getClass().getClassLoader(),
            new Class[]{DataSource.class},
            (proxy, method, args) -> method.invoke(useDatasource1 ? ds1 : ds2, args));
}

Sample code to test it out

@Bean
ApplicationRunner applicationRunner(PersonRepo repo) {
    return args -> {

        repo.save(new Person(1, "dapeng"));
        System.out.println("ds1: " + repo.findAll());

        useDatasource1 = false;
        System.out.println("ds2: " + repo.findAll());

        useDatasource1 = true;
        System.out.println("ds1: " + repo.findAll());

    };
}

When we actually run the project

ds1: [Person(id=1, name=dapeng)]
ds2: []
ds1: [Person(id=1, name=dapeng)]

How to run

mvn spring-boot:run