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Author Archives: Vlad Mihalcea

Vlad Mihalcea is a software architect passionate about software integration, high scalability and concurrency challenges.

EAGER fetching is a code smell


Introduction Hibernate fetching strategies can really make a difference between an application that barely crawls and a highly responsive one. In this post I’ll explain why you should prefer query based fetching instead of global fetch plans. Fetching 101 Hibernate defines four association retrieving strategies:     Fetching Strategy Description Join The association is OUTER JOINED in the original SELECT ...

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The downside of version-less optimistic locking

Introduction In my previous post I demonstrated how you can scale optimistic locking through write-concerns splitting. Version-less optimistic locking is one lesser-known Hibernate feature. In this post I’ll explain both the good and the bad parts of this approach.         Version-less optimistic locking Optimistic locking is commonly associated with a logical or physical clocking sequence, for both ...

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Spring request-level memoization


Introduction Memoization is a method-level caching technique for speeding-up consecutive invocations. This post will demonstrate how you can achieve request-level repeatable reads for any data source, using Spring AOP only.         Spring Caching Spring offers a very useful caching abstracting, allowing you do decouple the application logic from the caching implementation details. Spring Caching uses an application-level ...

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A beginner’s guide to Java time zone handling

Basic time notions Most web applications have to support different time-zones and properly handling time-zones is no way easy. To make matters worse, you have to make sure that timestamps are consistent across various programming languages (e.g. JavaScript on the front-end, Java in the middle-ware and MongoDB as the data repository). This post aims to explain the basic notions of ...

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An entity modelling strategy for scaling optimistic locking

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 ...

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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 ...

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Hibernate application-level repeatable reads

Introduction In my previous post I described how application-level transactions offer a suitable concurrency control mechanism for long conversations. All entities are loaded within the context of a Hibernate Session, acting as a transactional write-behind cache. A Hibernate persistence context can hold one and only one reference of a given entity. The first level cache guarantees session-level repeatable reads. If ...

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MongoDB Incremental Migration Scripts

Introduction An incremental software development process requires an incremental database migration strategy. I remember working on an enterprise application where the hibernate.hbm2ddl.auto was the default data migration tool. Updating the production environment required intensive preparation and the migration scripts were only created on-the-spot. An unforeseen error could have led production data corruption. Incremental updates to the rescue The incremental database ...

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Integration testing done right with Embedded MongoDB

Introduction Unit testing requires isolating individual components from their dependencies. Dependencies are replaced with mocks, which simulate certain use cases. This way, we can validate the in-test component behavior across various external context scenarios. Web components can be unit tested using mock business logic services. Services can be tested against mock data access repositories. But the data access layer is ...

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Logical vs physical clock optimistic locking

Introduction In my previous post I demonstrated why optimistic locking is the only viable solution for application-level transactions. Optimistic locking requires a version column that can be represented as: a physical clock (a timestamp value taken from the system clock) a logical clock (an incrementing numeric value) This article will demonstrate why logical clocks are better suited for optimistic locking ...

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