Optimistic locking retry with MongoDB

In my previous post I talked about the benefit of employing optimistic locking for MongoDB batch processors. As I wrote before, the optimistic locking exception is a recoverable one, as long as we fetch the latest Entity, we update and save it.

Because we are using MongoDB we don’t have to worry about local or XA transactions. In a future post I’ll demonstrate how you can build the same mechanism when using JPA.

The Spring framework offers a very good AOP support and therefore it makes easy implementing an automatic retry mechanism, and this is how I did it.

We first define a Retry annotation

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Retry {

    Class<? extends Exception>[] on();

    int times() default 1;
}

and we annotate our business logic methods like

@Retry(times = 10, on = org.springframework.dao.OptimisticLockingFailureException.class)
public Product updateName(Long id, String name) {
	Product product = productRepository.findOne(id);
	product.setName(name);
	LOGGER.info("Updating product {} name to {}", product, name);
	return productRepository.save(product);
}

Then we only need an AOP Aspect to intercept the business logic calls, and retry in case of optimistic locking detection.

@Aspect
public class OptimisticConcurrencyControlAspect {

    private static final Logger LOGGER = LoggerFactory.getLogger(OptimisticConcurrencyControlAspect.class);

    @Around("@annotation(vladmihalcea.concurrent.Retry)")
    public Object retry(ProceedingJoinPoint pjp) throws Throwable {
        Retry retryAnnotation = getRetryAnnotation(pjp);
        return (retryAnnotation != null) ? proceed(pjp, retryAnnotation) : proceed(pjp);
    }

    private Object proceed(ProceedingJoinPoint pjp) throws Throwable {
        return pjp.proceed();
    }

    private Object proceed(ProceedingJoinPoint pjp, Retry retryAnnotation) throws Throwable {
        int times = retryAnnotation.times();
        Class<? extends Throwable>[] retryOn = retryAnnotation.on();
        Assert.isTrue(times > 0, "@Retry{times} should be greater than 0!");
        Assert.isTrue(retryOn.length > 0, "@Retry{on} should have at least one Throwable!");
        LOGGER.info("Proceed with {} retries on {}", times, Arrays.toString(retryOn));
        return tryProceeding(pjp, times, retryOn);
    }

    private Object tryProceeding(ProceedingJoinPoint pjp, int times, Class<? extends Throwable>[] retryOn) throws Throwable {
        try {
            return proceed(pjp);
        } catch (Throwable throwable) {
            if(isRetryThrowable(throwable, retryOn) && times-- > 0) {
                LOGGER.info("Optimistic locking detected, {} remaining retries on {}", times, Arrays.toString(retryOn));
                return tryProceeding(pjp, times, retryOn);
            }
            throw throwable;
        }
    }

    private boolean isRetryThrowable(Throwable throwable, Class<? extends Throwable>[] retryOn) {
        Throwable[] causes = ExceptionUtils.getThrowables(throwable);
        for(Throwable cause : causes) {
            for(Class<? extends Throwable> retryThrowable : retryOn) {
                if(retryThrowable.isAssignableFrom(cause.getClass())) {
                    return true;
                }
            }
        }
        return false;
    }

    private Retry getRetryAnnotation(ProceedingJoinPoint pjp) throws NoSuchMethodException {
        MethodSignature signature = (MethodSignature) pjp.getSignature();
        Method method = signature.getMethod();
        Retry retryAnnotation = AnnotationUtils.findAnnotation(method, Retry.class);

        if(retryAnnotation != null) {
            return retryAnnotation;
        }

        Class[] argClasses = new Class[pjp.getArgs().length];
        for (int i = 0; i < pjp.getArgs().length; i++) {
            argClasses[i] = pjp.getArgs()[i].getClass();
        }
        method = pjp.getTarget().getClass().getMethod(pjp.getSignature().getName(), argClasses);
        return AnnotationUtils.findAnnotation(method, Retry.class);
    }
}

This utility is part of my db-util project along with the JPA optimistic concurrency control retry mechanism.

Since it’s already available in Maven Central Repository, you can easily use it by just adding this dependency to your pom.xml:

<dependency>
	<groupId>com.vladmihalcea</groupId>
	<artifactId>db-util</artifactId>
	<version>0.0.1</version>
</dependency>

The test starts 10 treads competing for saving a Product, and this is the test log.

	Line 492: INFO  [Thread-9]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 495: INFO  [Thread-3]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 504: INFO  [Thread-8]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 505: INFO  [Thread-11]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 507: INFO  [Thread-10]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 513: INFO  [Thread-5]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 523: INFO  [Thread-4]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 529: INFO  [Thread-3]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 8 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 586: INFO  [Thread-10]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 8 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 682: INFO  [Thread-5]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 8 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 683: INFO  [Thread-3]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 7 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 686: INFO  [Thread-8]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 8 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 702: INFO  [Thread-3]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 6 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 752: INFO  [Thread-5]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 7 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 756: INFO  [Thread-8]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 7 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]
	Line 859: INFO  [Thread-5]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 6 remaining retries on [class org.springframework.dao.OptimisticLockingFailureException]

Code available on GitHub.

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