Speed Up Your Gradle Builds with the Build Cache: A Practical Guide

The Problem – Long Build Times in Multi‑Project Gradle Builds

In a typical monorepo or large Gradle multi‑project setup, incremental builds still can take a minute or more. Each task recomputes its output even if the source hasn’t changed because the build system has no way to remember that the previous result was still valid.

The Thesis – Build Cache Reuses Deterministic Task Outputs

What Is the Build Cache?

The Gradle Build Cache is a storage layer that keeps the outputs of tasks that declare deterministic inputs. When the same task runs again with identical inputs, Gradle can fetch the cached output instead of re‑executing the task.

When Does It Work?

Gradle automatically marks tasks as cacheable if:

• The task’s inputs and outputs are fully deterministic.
• The task’s implementation is deterministic (no random data, timestamps, or external state).

Typical tasks like compileJava or jar are cacheable by default.

Configuring the Cache

Gradle supports two cache scopes:

• Local cache – stored on the developer’s machine under ~/.gradle/caches/build-cache-1.
• Remote cache – a shared server accessible by all CI agents.

Enabling the cache is as simple as adding a property to gradle.properties or configuring the buildCache block in settings.gradle:

// gradle.properties
org.gradle.caching=true

// settings.gradle
buildCache {
    local {
        enabled = true
    }
    remote(HttpBuildCache) {
        url = uri("https://cache.example.com")
        push = true
        // Optional authentication
        credentials {
            username = "user"
            password = "pass"
        }
    }
}

Worked Example – Enabling a Remote Cache for a Kotlin Multiplatform Project

Suppose you have a Kotlin Multiplatform library that targets JVM and JS. The project contains two sub‑projects: shared and app. You want CI agents to share compiled artifacts.

Project layout:

/buildSrc
/shared
/app
/gradle.properties
/settings.gradle

1. Add the cache property to gradle.properties:

org.gradle.caching=true

2. Configure the remote cache in settings.gradle:

buildCache {
    local {
        enabled = true
    }
    remote(HttpBuildCache) {
        url = uri("https://ci-cache.example.com")
        push = true
        credentials {
            username = "ci-user"
            password = "${System.getenv('CI_CACHE_PASSWORD')}"
        }
    }
}

3. Run a build on CI with the flag --build-cache:

./gradlew assemble --build-cache

Gradle will log lines like Cache hit for task :shared:compileKotlin or Cache miss for task :app:compileKotlin. The first run pushes the output to the remote server; subsequent runs on other agents reuse that output.

Trade‑offs and Limitations

• Non‑deterministic inputs: Tasks that read system time, random numbers, or external state will never hit the cache. Ensure tasks are deterministic or exclude them from caching.
• Sensitive artifacts: Signed binaries or credentials may inadvertently be cached. Use cacheable = false or configure exclusion rules.
• Remote security: The remote cache endpoint must be secured with TLS and authentication. Misconfigured endpoints can expose build artifacts.
• Cache size management: Local caches grow over time. Configure buildCache.local.removeUnusedEntriesAfterDays to clean old entries.

How to Verify Cache Usage

1. Run a build with --build-cache and watch the console for Cache hit or Cache miss messages.
2. Enable a build scan (e.g., ./gradlew -Dorg.gradle.scan=true build) and inspect the "Build cache" section to see hit/miss statistics and the server used.
3. Clear the local cache with gradle --no-build-cache clean build and confirm that all tasks re‑execute, indicating the cache was previously used.

Actionable Takeaway

Enabling Gradle’s Build Cache is a low‑effort, high‑impact change: add org.gradle.caching=true, configure a remote server if you have CI, and run your builds with --build-cache. Verify hits via console logs or build scans, and monitor cache size and security. Once in place, you’ll see build time reductions of 30–70% on typical multi‑project builds, freeing up developer and CI time for more valuable work.