@Scheduled ve ShedLock — Cron İşi Kaç Pod'da Çalışıyor?

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@Configuration
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@EnableScheduling
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@EnableSchedulerLock(defaultLockAtMostFor = "PT10M")
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class SchedulingConfig {
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    @Bean
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    LockProvider lockProvider(DataSource dataSource) {
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        return new JdbcTemplateLockProvider(
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                JdbcTemplateLockProvider.Configuration.builder()
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                        .withJdbcTemplate(new JdbcTemplate(dataSource))
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                        .usingDbTime()      // lock_until computed by the database, not by pod clocks
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                        .build());
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    }
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}

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@Component
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class InstallmentReminderJob {
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    private final ReminderService reminders;
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    private final AtomicLong lastSuccess = new AtomicLong();
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    InstallmentReminderJob(ReminderService reminders, MeterRegistry meters) {
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        this.reminders = reminders;
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        // Alert when this stops moving: silent failures are the real risk of scheduled jobs.
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        meters.gauge("loan.reminders.last.success.epoch", lastSuccess);
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    }
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    @Scheduled(cron = "0 * * * * *", zone = "Europe/Istanbul")
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    @SchedulerLock(name = "installmentReminders", lockAtMostFor = "PT10M", lockAtLeastFor = "PT30S")
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    public void run() {
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        LockAssert.assertLocked();          // fails loudly if someone calls run() without the lock
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        reminders.sendDue(Instant.now(), 200);
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        lastSuccess.set(Instant.now().getEpochSecond());
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        // A full batch of 200 means more are waiting: the next minute picks them up.
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        // No unbounded loop inside the lock, so a run never outlives lockAtMostFor.
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    }
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}

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@Service
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class ReminderService {
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    private final InstallmentRepository installments;
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    private final SmsGateway sms;
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    ReminderService(InstallmentRepository installments, SmsGateway sms) {
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        this.installments = installments;
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        this.sms = sms;
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    }
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    @Transactional
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    public int sendDue(Instant now, int batchSize) {
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        // Installments due within three days whose reminder_sent_at IS NULL.
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        // That condition makes the job idempotent: a second run finds nothing to do.
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        List<Installment> due = installments.findDueSoonWithoutReminder(now, Duration.ofDays(3), Limit.of(batchSize));
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        for (Installment installment : due) {
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            sms.send(installment.customerPhone(), Templates.INSTALLMENT_REMINDER,
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                    installment.dueDate(), installment.amount());
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            installment.markReminderSent(now);
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        }
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        return due.size();
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    }
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}

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CREATE TABLE shedlock (
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    name       VARCHAR(64)  NOT NULL PRIMARY KEY,
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    lock_until TIMESTAMP    NOT NULL,
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    locked_at  TIMESTAMP    NOT NULL,
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    locked_by  VARCHAR(255) NOT NULL
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);

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spring:
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  task:
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    scheduling:
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      pool:
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        size: 4               # default is 1: one slow job would delay every other job
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      thread-name-prefix: sched-
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      shutdown:
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        await-termination: true
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        await-termination-period: 30s