Introduction

In this article, I will discuss how we can implement an automatic Retry mechanism when dealing with the JPA OptimisticLockException.

You can find the introductory part here and the MongoDB implementation here.

Retry

JPA requires running the Persistence Context code inside a transaction, and if our Transaction Manager catches a RuntimeException, it initiates the rollback process. This makes the Persistence Context unusable since we should discard it along with the rolled-back Transaction.

Therefore it’s safer to retry the business logic operation when we are not within a running transaction.

For this, we altered our @Retry annotation like this:

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

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

    int times() default 1;
}

The Aspect was also changed to take into consideration the new annotation property.

private Object proceed(
        ProceedingJoinPoint pjp, 
        Retry retryAnnotation) 
    throws Throwable {
    int times = retryAnnotation.times();
    Class<? extends Throwable>[] retryOn = retryAnnotation.on();
    if (times <= 0) {
        throw new IllegalArgumentException(
            "@Retry{times} should be greater than 0!"
        );
    }
    if (retryOn.length <= 0) {
        throw new IllegalArgumentException(
            "@Retry{on} should have at least one Throwable!"
        );
    }

    LOGGER.debug(
        "Proceed with {} retries on {}", 
        times, 
        Arrays.toString(retryOn)
    );

    return tryProceeding(pjp, times, retryOn);
}

This utility is part of my Hypersistence Utils 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>io.hypersistence</groupId>
    <artifactId>hypersistence-utils-hibernate-55</artifactId>
    <version>${hypersistence-utils.version}</version>
</dependency>

You can configure the optimistic retry as simply as this:

@Retry(times = 10, on = OptimisticLockException.class)
public Product updateName(
        final Long id, 
        final String name) {
    return transactionTemplate.execute(
        new TransactionCallback<Product>() {
            @Override
            public Product doInTransaction(TransactionStatus status) {
                Product product = entityManager.find(Product.class, id);
                product.setName(name);
               
                LOGGER.info("Updating product {} name to {}", product, name);		
                return product;
            }
        }
    );
}

Running a JUnit test that schedules 10 threads to update the same entity will generate optimistic locking exceptions, and this what the test outputs.

Line 102: INFO  [Thread-3]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class javax.persistence.OptimisticLockException]
Line 103: INFO  [Thread-12]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class javax.persistence.OptimisticLockException]
Line 104: INFO  [Thread-9]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class javax.persistence.OptimisticLockException]
Line 105: INFO  [Thread-6]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class javax.persistence.OptimisticLockException]
Line 109: INFO  [Thread-9]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 8 remaining retries on [class javax.persistence.OptimisticLockException]
Line 110: INFO  [Thread-7]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class javax.persistence.OptimisticLockException]
Line 114: INFO  [Thread-3]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 8 remaining retries on [class javax.persistence.OptimisticLockException]
Line 115: INFO  [Thread-5]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class javax.persistence.OptimisticLockException]
Line 117: INFO  [Thread-11]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 9 remaining retries on [class javax.persistence.OptimisticLockException]
Line 118: INFO  [Thread-6]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 8 remaining retries on [class javax.persistence.OptimisticLockException]
Line 123: INFO  [Thread-7]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 8 remaining retries on [class javax.persistence.OptimisticLockException]
Line 124: INFO  [Thread-5]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 8 remaining retries on [class javax.persistence.OptimisticLockException]
Line 126: INFO  [Thread-11]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 8 remaining retries on [class javax.persistence.OptimisticLockException]
Line 129: INFO  [Thread-5]: v.c.a.OptimisticConcurrencyControlAspect - Optimistic locking detected, 7 remaining retries on [class javax.persistence.OptimisticLockException]

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Conclusion

So we reused the same optimistic locking retry logic we first implemented for our MongoDB batch processors, therefore proving we can easily implement such behavior even for JPA repositories.

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