Chronicle Map for Java: The Complete Guide with Examples

Chronicle Map is a high-performance, off-heap implementation of ConcurrentMap for Java, developed by Chronicle Software. Unlike standard HashMap or ConcurrentHashMap, which store data in the JVM heap, Chronicle Map places data directly in RAM outside the managed heap. This eliminates garbage collection (GC) overhead and ensures predictable latency even when working with massive datasets (gigabytes to terabytes).

This library is ideal for scenarios requiring low latency, high throughput, and data that must not impact GC pause times. Typical use cases include financial systems (trading platforms), caching, real-time systems, session storage, and any application where deterministic performance is critical. Chronicle Map supports multi-threaded access, key/value serialization, and can be configured for persistence (saving data to disk).

In this article, we'll dive deep into setup, key methods, provide plenty of working examples, and share performance tips. By the end, you'll be able to confidently use Chronicle Map in your Java projects.

1. Setup & Installation

Chronicle Map is distributed via Maven Central. To use it in your project, add the following dependency to your pom.xml (Maven):

<dependency>
    <groupId>net.openhft</groupId>
    <artifactId>chronicle-map</artifactId>
    <version>3.25ea0</version> <!-- Check Maven Central for the latest version -->
</dependency>

If you're using Gradle, add this line to your build.gradle:

implementation 'net.openhft:chronicle-map:3.25ea0'

2. Quick Start — Minimal Working Example

Let's create a simple map that stores "username" (String) to "number of logins" (Integer) pairs. This example demonstrates basic setup, insertion, and retrieval.