Spring: @Scheduled runs on a single thread by default

One slow job delays every other scheduled job unless you give the scheduler a pool.

Code

@EnableScheduling
@Configuration
class SchedulingConfig {
    @Bean
    TaskScheduler taskScheduler() {
        var s = new ThreadPoolTaskScheduler();
        s.setPoolSize(5);            // without this: 1
        return s;
    }
}

@Scheduled(fixedDelay = 60_000)
void reap() { ... }

@Scheduled(cron = "0 0 3 * * *", zone = "Asia/Kolkata")
void nightly() { ... }

Output

Default pool size is 1: a 10-minute job blocks the reaper for 10 minutes.
fixedDelay waits AFTER completion; fixedRate waits from the start.

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Published 2026-08-11