Java Performance Workshop with Peter Lawrey
Peter Lawrey at IT Days I’ve just come back from a Java Performance Workshop held by Peter Lawrey at Cluj-Napoca IT Days. Peter Lawrey is a well-known Java StackOverflow user and the creator of Java Chronicle open-source library. Of Java and low latency Little’s Law defines concurrency as: To increase throughput we can either: increase server resources (scaling vertically or horizontally) decrease latency (improve performance) While enterprise applications are usually designed for scaling, trading systems focus on lowering latencies. As surprising as it may sound, most trading systems, I’ve heard of, are… Read More
How to address the OptimisticLockException in JPA and Hibernate
Introduction Application-level repeatable reads are suitable for preventing lost updates in web conversations. Enabling entity-level optimistic locking is fairly easy. You just have to mark one logical-clock property (usually an integer counter) with the JPA @Version annotation and Hibernate takes care of the rest. The catch Optimistic locking discards all incoming changes that are relative to an older entity version. But everything has a cost and optimistic locking makes no difference. The optimistic concurrency control mechanism takes an all-or-nothing approach even for non-overlapping changes. If two concurrent transactions are changing distinct entity… Read More
Hibernate collections optimistic locking
Introduction Hibernate provides an optimistic locking mechanism to prevent lost updates even for long-conversations. In conjunction with an entity storage, spanning over multiple user requests (extended persistence context or detached entities) Hibernate can guarantee application-level repeatable-reads. The dirty checking mechanism detects entity state changes and increments the entity version. While basic property changes are always taken into consideration, Hibernate collections are more subtle in this regard. Owned vs Inverse collections In relational databases, two records are associated with a foreign key reference. In this relationship, the referenced record is the parent while… Read More
