While investigating @EventListeners in spring I’ve noticed very interesting annotation - @DomainEvents. In this post I’m going to check what can be achieved using @DomainEvents annotation and how to effectively use it with old good JPA. Let’s start with short introduction to domain event idea if you are not yet familiar with it. Now let’s go back to the @DomainEvents annotation in spring-data. Spring-data by default provides support for this annotation and it’s complementary annotation @AfterDomainEventPublication.
Working with a lot of data using plain JPA or hibernate or spring-data is possible, it does work and usually, it doesn’t require a lot of extra coding. Starting small is the fastest way of getting things done but you must be aware of few things that might shoot you in the foot.
Optimistic locking is concurrency control method that allows to execute multiple transactions simultaneously as long as they don’t interfere which each other. That’s definition from wikipedia. You probably already know that Hibernate supports optimistic locking and all you have to do in order to implement optimistic locking in you app is to add @Version on number or timestamp field and you are good to go. Right?
A few days ago I’ve stumbled upon SQL query performance issue. Git claims that I was the author so maybe that’s the reason I remember this feature. There was like 3 classes, everything was super easy and super fast all I needed to do was to let Hibernate do its thing. Then time passed, new features were requested, the model becomes more complex, the number of rows increased to ~4 million and original query became too slow.
When working on query optimization I was really happy to find that detailed tests are in place. With proper test setup I was able to test my new query to make sure all requirements are met and then quickly copy paste query to sqldeveloper run it on a test environment and verify if performance is acceptable. It wasn’t simple query and it took me some time to figure out how to make it quick and work exactly as old one. That was the time I was really glad that we invested in detailed unit tests in the beginning.