Over a million developers have joined DZone.
{{announcement.body}}
{{announcement.title}}

The Anatomy of Hibernate Dirty Checking

DZone's Guide to

The Anatomy of Hibernate Dirty Checking

· Java Zone
Free Resource

Bitbucket is for the code that takes us to Mars, decodes the human genome, or drives your next car. What will your code do? Get started with Bitbucket today, it's free.

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 is loaded, Hibernate makes an additional copy of all entity property values. At flush time, every managed entity property is matched against the loading-time snapshot value:

DefaultFlushEventFlow

So the number of individual dirty checks is given by the following formula:

N = \sum\limits_{k=1}^n p_{k}

where

n = The number of managed entities
p = The number of entities of a given entity

Even if only one property of a single entity has ever changed, Hibernate will still check all managed entities. For a large number of managed entities, the default dirty checking mechanism may have a significant CPU and memory footprint. Since the initial entity snapshot is held separately, the persistence context requires twice as much memory as all managed entities would normally occupy.

Bytecode instrumentation

A more efficient approach would be to mark dirty properties upon value changing. Analogue to the original deep comparison strategy, it’s good practice to decouple the domain model structures from the change detection logic. The automatic entity change detection mechanism is a cross-cutting concern, that can be woven either at build-time or at runtime.

The entity class can be appended with bytecode level instructions implementing the automatic dirty checking mechanism.

Weaving types

The bytecode enhancement can happen at:

  • Build-time

    After the hibernate entities are compiled, the build tool (e.g. ANT, Maven) will insert bytecode level instructions into each compiled entity class. Because the classes are enhanced at build-time, this process exhibits no extra runtime penalty. Testing can be done against enhanced class versions, so that the actual production code is validated before the project gets built.

  • Runtime

    The runtime weaving can be done using:

Towards a default bytecode enhancement dirty checking

Hibernate 3 has been offering bytecode instrumentation through an ANT target but it never became mainstream and most Hibernate projects are still currently using the default deep comparison approach.

While other JPA providers (e.g. OpenJPA, DataNucleus) have been favouring the bytecode enhancement approach, Hibernate has only recently started moving in this direction, offering better build-time options and even custom dirty checking callbacks.

In my next post I’ll show you how you can customize the dirty checking mechanism with your own application specific strategy.

If you have enjoyed reading my article and you’re looking forward to getting instant email notifications of my latest posts, you just need to follow my blog.

Bitbucket is the Git solution for professional teams who code with a purpose, not just as a hobby. Get started today, it's free.

Topics:

Published at DZone with permission of Vlad Mihalcea, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

THE DZONE NEWSLETTER

Dev Resources & Solutions Straight to Your Inbox

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.

X

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}