Understanding the Default Scheduler Pool Size in Spring Boot

What is the default scheduler pool size in Spring Boot?

@Service
public class ZipFileTesterAsync {

    @Scheduled(fixedDelay = 60000, initialDelay = 500)
    public void run() throws Exception {
        System.out.println("import 1");
        TimeUnit.MINUTES.sleep(1);
        System.out.println("import 1 finished");
    }

    @Scheduled(fixedDelay = 60000, initialDelay = 1000)
    public void run2() throws Exception {
        System.out.println("import 2");
        TimeUnit.MINUTES.sleep(1);
    }
}

In Spring Boot, when using the `@Scheduled` annotation without a specific configuration, tasks by default execute in a single-threaded pool. This means that if one scheduled task is running, others will wait to execute until the current one completes.

@Configuration
public class SchedulerConfig {

    @Bean
    public TaskScheduler taskScheduler() {
        ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
        scheduler.setPoolSize(5); // Set your desired pool size
        scheduler.setThreadNamePrefix("ScheduledTask-");
        return scheduler;
    }
} 

@Service
public class ZipFileTesterAsync {

    @Scheduled(fixedDelay = 60000, initialDelay = 500)
    public void run() throws Exception {
        System.out.println("import 1");
        TimeUnit.MINUTES.sleep(1);
        System.out.println("import 1 finished");
    }

    @Scheduled(fixedDelay = 60000, initialDelay = 1000)
    public void run2() throws Exception {
        System.out.println("import 2");
        TimeUnit.MINUTES.sleep(1);
    }
}

Causes

• The default thread pool for scheduled tasks is a single-thread executor, which means only one task is executed at a time.
• If a scheduled method takes a long time to execute, it blocks other scheduled methods from running concurrently.

Solutions

• To enable parallel execution of scheduled tasks, you can configure a task scheduler with a thread pool size greater than one.
• You can define a `ThreadPoolTaskScheduler` bean in your configuration class to set a custom thread pool size.

Mistake: Not configuring a ThreadPoolTaskScheduler, leading to sequential execution.

Solution: Define a TaskScheduler bean with multiple threads to allow concurrent execution of scheduled tasks.

Mistake: Using long-running tasks within a scheduled method without proper thread management.

Solution: Optimize task execution time or split tasks into smaller, non-blocking calls.