Vlad Mihalcea

Spring request-level memoization

Are you struggling with performance issues in your Spring, Jakarta EE, or Java EE application?

Imagine having a tool that could automatically detect performance issues in your JPA and Hibernate data access layer long before pushing a problematic change into production!

With the widespread adoption of AI agents generating code in a heartbeat, having such a tool that can watch your back and prevent performance issues during development, long before they affect production systems, can save your company a lot of money and make you a hero!

Hypersistence Optimizer is that tool, and it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, Micronaut, or Play Framework.

So, rather than allowing performance issues to annoy your customers, you are better off preventing those issues using Hypersistence Optimizer and enjoying spending your time on the things that you love!

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 scope, so for a request-only memoization we need to take a DIY approach.

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Java Performance Workshop with Peter Lawrey

Are you struggling with performance issues in your Spring, Jakarta EE, or Java EE application?

Imagine having a tool that could automatically detect performance issues in your JPA and Hibernate data access layer long before pushing a problematic change into production!

With the widespread adoption of AI agents generating code in a heartbeat, having such a tool that can watch your back and prevent performance issues during development, long before they affect production systems, can save your company a lot of money and make you a hero!

Hypersistence Optimizer is that tool, and it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, Micronaut, or Play Framework.

So, rather than allowing performance issues to annoy your customers, you are better off preventing those issues using Hypersistence Optimizer and enjoying spending your time on the things that you love!

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:

Throughput = \dfrac{Served Requests}{Latency}

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 actually written in Java. Java automatic memory management is a double-edged sword, since it trades simplicity for flexibility.

A low latency system worse nightmare is a stop-of-the-world process, like a garbage collector major collection. So in order to avoid such situations, you must go off-heap.

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A beginner’s guide to Java time zone handling

Are you struggling with performance issues in your Spring, Jakarta EE, or Java EE application?

Imagine having a tool that could automatically detect performance issues in your JPA and Hibernate data access layer long before pushing a problematic change into production!

With the widespread adoption of AI agents generating code in a heartbeat, having such a tool that can watch your back and prevent performance issues during development, long before they affect production systems, can save your company a lot of money and make you a hero!

Hypersistence Optimizer is that tool, and it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, Micronaut, or Play Framework.

So, rather than allowing performance issues to annoy your customers, you are better off preventing those issues using Hypersistence Optimizer and enjoying spending your time on the things that you love!

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 absolute and relative time.

Epoch

An epoch is a an absolute time reference. Most programming languages (e.g Java, JavaScript, Python) use the Unix epoch (Midnight 1 January 1970) when expressing a given timestamp as the number of milliseconds elapsed since a fixed point-in-time reference.

Relative numerical timestamp

The relative numerical timestamp is expressed as the number of milliseconds elapsed since the epoch.

Time zone

The coordinated universal time (UTC) is the most common time standard. The UTC time zone (equivalent to GMT) represents the time reference all other time zones relate to (through a positive/negative offset).

UTC time zone is commonly referred to as Zulu time (Z) or UTC+0. Japan’s time zone is UTC+9 and the Honolulu time zone is UTC-10. At the time of Unix epoch (1 January 1970 00:00 UTC time zone), it was 1 January 1970 09:00 in Tokyo and 31 December 1969 14:00 in Honolulu.

ISO 8601

ISO 8601 is the most widespread date/time representation standard and it uses the following date/time formats:

Time zone Notation
UTC 1970-01-01T00:00:00.000+00:00
UTC Zulu time 1970-01-01T00:00:00.000Z
Tokio 1970-01-01T09:00:00.000+09:00
Honolulu 1969-12-31T14:00:00.000-10:00

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How to address the OptimisticLockException in JPA and Hibernate

Are you struggling with performance issues in your Spring, Jakarta EE, or Java EE application?

Imagine having a tool that could automatically detect performance issues in your JPA and Hibernate data access layer long before pushing a problematic change into production!

With the widespread adoption of AI agents generating code in a heartbeat, having such a tool that can watch your back and prevent performance issues during development, long before they affect production systems, can save your company a lot of money and make you a hero!

Hypersistence Optimizer is that tool, and it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, Micronaut, or Play Framework.

So, rather than allowing performance issues to annoy your customers, you are better off preventing those issues using Hypersistence Optimizer and enjoying spending your time on the things that you love!

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 property subsets, then there’s no risk of losing updates.

Two concurrent updates, starting from the same entity version are always going to collide. It’s only the first update that’s going to succeed, the second one failing with an optimistic locking exception. This strict policy acts as if all changes are overlapping. For highly concurrent write scenarios, this single-version check strategy can lead to a large number of roll-backed updates.

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Hibernate collections optimistic locking

Are you struggling with performance issues in your Spring, Jakarta EE, or Java EE application?

Imagine having a tool that could automatically detect performance issues in your JPA and Hibernate data access layer long before pushing a problematic change into production!

With the widespread adoption of AI agents generating code in a heartbeat, having such a tool that can watch your back and prevent performance issues during development, long before they affect production systems, can save your company a lot of money and make you a hero!

Hypersistence Optimizer is that tool, and it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, Micronaut, or Play Framework.

So, rather than allowing performance issues to annoy your customers, you are better off preventing those issues using Hypersistence Optimizer and enjoying spending your time on the things that you love!

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 the referencing row (the foreign key side) is the child. A non-null foreign key may only reference an existing parent record.

In the Object-oriented space, this association can be represented in both directions. We can have a many-to-one reference from a child to parent and the parent can also have a one-to-many children collection.

Because both sides could potentially control the database foreign key state, we must ensure that only one side is the owner of this association. Only the owning side state changes are propagated to the database. The non-owning side has been traditionally referred as the inverse side.

Next, I’ll describe the most common ways of modeling this association.

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How does Hibernate guarantee application-level repeatable reads

Are you struggling with performance issues in your Spring, Jakarta EE, or Java EE application?

Imagine having a tool that could automatically detect performance issues in your JPA and Hibernate data access layer long before pushing a problematic change into production!

With the widespread adoption of AI agents generating code in a heartbeat, having such a tool that can watch your back and prevent performance issues during development, long before they affect production systems, can save your company a lot of money and make you a hero!

Hypersistence Optimizer is that tool, and it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, Micronaut, or Play Framework.

So, rather than allowing performance issues to annoy your customers, you are better off preventing those issues using Hypersistence Optimizer and enjoying spending your time on the things that you love!

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 to a given entity. The first level cache guarantees session-level repeatable reads.

If the conversation spans over multiple requests we can have application-level repeatable reads. Long conversations are inherently stateful so we can opt for detached objects or long persistence contexts. But application-level repeatable reads require an application-level concurrency control strategy such as optimistic locking.

The catch

But this behavior may prove unexpected at times.

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MongoDB Incremental Migration Scripts

Are you struggling with performance issues in your Spring, Jakarta EE, or Java EE application?

Imagine having a tool that could automatically detect performance issues in your JPA and Hibernate data access layer long before pushing a problematic change into production!

With the widespread adoption of AI agents generating code in a heartbeat, having such a tool that can watch your back and prevent performance issues during development, long before they affect production systems, can save your company a lot of money and make you a hero!

Hypersistence Optimizer is that tool, and it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, Micronaut, or Play Framework.

So, rather than allowing performance issues to annoy your customers, you are better off preventing those issues using Hypersistence Optimizer and enjoying spending your time on the things that you love!

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 update is a technical feature that needs to be addressed in the very first application development iterations.

We used to develop our own custom data migration implementations and spending time on writing/supporting frameworks is always working against your current project budget.

A project must be packed with both application code and all associated database schema/data updates scripts. Using incremental migration scripts allows us to automate the deployment process and to take advantage of continuous delivery.

Nowadays you don’t have to implement data migration tools, Flyway does a better job than all our previous custom frameworks. All database schema and data changes have to be recorded in incremental update scripts following a well-defined naming convention.

A RDBMS migration plan addresses both schema and data changes. It’s always good to separate schema and data changes. Integration tests might only use the schema migration scripts in conjunction with test-time related data.

Flyway supports all major relational database systems but for NoSQL (e.g. MongoDB) you need to look somewhere else.

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Integration testing done right with Embedded MongoDB

Are you struggling with performance issues in your Spring, Jakarta EE, or Java EE application?

Imagine having a tool that could automatically detect performance issues in your JPA and Hibernate data access layer long before pushing a problematic change into production!

With the widespread adoption of AI agents generating code in a heartbeat, having such a tool that can watch your back and prevent performance issues during development, long before they affect production systems, can save your company a lot of money and make you a hero!

Hypersistence Optimizer is that tool, and it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, Micronaut, or Play Framework.

So, rather than allowing performance issues to annoy your customers, you are better off preventing those issues using Hypersistence Optimizer and enjoying spending your time on the things that you love!

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 not a good candidate for unit testing because database statements need to be validated against an actual running database system.

Integration testing database options

Ideally, our tests should run against a production-like database. But using a dedicated database server is not feasible, as we most likely have more than one developer to run such integration test-suites. To isolate concurrent test runs, each developer would require a dedicated database catalog. Adding a continuous integration tool makes matters worse since more tests would have to be run in parallel.

Lesson 1: We need a forked test-suite bound database

When a test suite runs, a database must be started and only made available to that particular test-suite instance. Basically we have the following options:

  • An in-memory embedded database
  • A temporary spawned database process

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Logical vs physical clock optimistic locking

Are you struggling with performance issues in your Spring, Jakarta EE, or Java EE application?

Imagine having a tool that could automatically detect performance issues in your JPA and Hibernate data access layer long before pushing a problematic change into production!

With the widespread adoption of AI agents generating code in a heartbeat, having such a tool that can watch your back and prevent performance issues during development, long before they affect production systems, can save your company a lot of money and make you a hero!

Hypersistence Optimizer is that tool, and it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, Micronaut, or Play Framework.

So, rather than allowing performance issues to annoy your customers, you are better off preventing those issues using Hypersistence Optimizer and enjoying spending your time on the things that you love!

Introduction

In this article, I’m going to explain how logical and physical clock versioning strategies work and why you should prefer using logical clocks for concurrency control.

Optimistic locking is a viable solution for preventing lost updates when running 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 mechanisms.

System time

The system time is provided by the internal clock of the current operating system. The programmable interval timer periodically sends an interrupt signal (with a frequency of 1.193182 MHz). The CPU receives the time interruption and increments a tick counter.

Both Unix and Windows record time as the number of ticks since a predefined absolute time reference (an epoch). The operating system clock resolution varies from 1ms (Android) to 100ns (Windows) and to 1ns (Unix).

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One year of blogging

Are you struggling with performance issues in your Spring, Jakarta EE, or Java EE application?

Imagine having a tool that could automatically detect performance issues in your JPA and Hibernate data access layer long before pushing a problematic change into production!

With the widespread adoption of AI agents generating code in a heartbeat, having such a tool that can watch your back and prevent performance issues during development, long before they affect production systems, can save your company a lot of money and make you a hero!

Hypersistence Optimizer is that tool, and it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, Micronaut, or Play Framework.

So, rather than allowing performance issues to annoy your customers, you are better off preventing those issues using Hypersistence Optimizer and enjoying spending your time on the things that you love!

Teaching is my way of learning

Exactly one year ago today, I wrote my very first blog post. It’s been such a long journey ever since, so it’s time to draw a line and review all my technical writing accomplishments.

I realized that sharing knowledge is a way of pushing myself to reason thoroughly on a particular subject. So, both my readers and I have something to learn from my writing. Finding time to think of future blog topics, researching particular subjects, writing code snippets and the ever-present pre-publishing reviews is worth the hassle.

Under the umbrella

The Internet is huge, so being heard is not something you would leave to chance. From the start, I knew that I needed to do more than writing high-quality articles. When nobody knows anything about you, your only chance is strategic marketing.

Several well-received articles, and Allen Coin proposed me for the Dev of the Week column.

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