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Author Archives: Vlad Mihalcea

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

The fastest way of drawing UML class diagrams

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A picture is worth a thousand words Understanding a software design proposal is so much easier once you can actually visualize it. While writing diagrams might take you an extra effort, the small time investment will pay off when others will require less time understanding your proposal. Software is a means, not a goal We are writing software to supports ...

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Preventing lost updates in long conversations

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Introduction All database statements are executed within the context of a physical transaction, even when we don’t explicitly declare transaction boundaries (BEGIN/COMMIT/ROLLBACK). Data integrity is enforced by the ACID properties of database transactions. Logical vs Physical transactions An logical transaction is an application-level unit of work that may span over multiple physical (database) transactions. Holding the database connection open throughout ...

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A beginner’s guide to database locking and the lost update phenomena

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Introduction A database is highly concurrent system. There’s always a chance of update conflicts, like when two concurring transactions try to update the same record. If there would be only one database transaction at any time then all operations would be executed sequentially. The challenge comes when multiple transactions try to update the same database rows as we still have ...

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Hibernate bytecode enhancement

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Introduction Now that you know the basics of Hibernate dirty checking, we can dig into enhanced dirty checking mechanisms. While the default graph-traversal algorithm might be sufficient for most use-cases, there might be times when you need an optimized dirty checking algorithm and instrumentation is much more convinient than building your own custom strategy.         Using Ant ...

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How to customize Hibernate dirty checking mechanism

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Introduction In my previous article I described the Hibernate automatic dirty checking mechanism. While you should always prefer it, there might be times when you want to add your own custom dirtiness detection strategy. Custom dirty checking strategies Hibernate offers the following customization mechanisms:   Hibernate Interceptor#findDirty() CustomEntityDirtinessStrategy A manual dirty checking exercise As an exercise, I’ll build a manual ...

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The anatomy of Hibernate dirty checking

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Introduction The persistence context enqueues entity state transitions that get translated to database statements upon flushing. For managed entities, Hibernate can auto-detect incoming changes and schedule SQL UPDATES on our behalf. This mechanism is called automatic dirty checking.           The default dirty checking strategy By default Hibernate checks all managed entity properties. Every time an entity ...

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The dark side of Hibernate AUTO flush

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Introduction Now that I described the the basics of JPA and Hibernate flush strategies, I can continue unraveling the surprising behavior of Hibernate’s AUTO flush mode. Not all queries trigger a Session flush Many would assume that Hibernate always flushes the Session before any executing query. While this might have been a more intuitive approach, and probably closer to the ...

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A beginner’s guide to JPA/Hibernate flush strategies

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Introduction In my previous post I introduced the entity state transitions Object-relational mapping paradigm. All managed entity state transitions are translated to associated database statements when the current Persistence Context gets flushed. Hibernate’s flush behavior is not always as obvious as one might think.       Write-behind Hibernate tries to defer the Persistence Context flushing up until the last ...

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A beginner’s guide to JPA/Hibernate entity state transitions

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Introduction Hibernate shifts the developer mindset from SQL statements to entity state transitions. Once an entity is actively managed by Hibernate, all changes are going to be automatically propagated to the database. Manipulating domain model entities (along with their associations) is much easier than writing and maintaining SQL statements. Without an ORM tool, adding a new column requires modifying all ...

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Hibernate hidden gem: the pooled-lo optimizer

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Introduction In this post we’ll uncover a sequence identifier generator combining identifier assignment efficiency and interoperability with other external systems (concurrently accessing the underlying database system). Traditionally there have been two sequence identifier strategies to choose from.         The sequence identifier, always hitting the database for every new value assignment. Even with database sequence preallocation we have ...

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