A normal log says: Cache restored from key: Linux-node-abc123
A debug-action-cache log says:
[debug] Checking cache for key: Linux-node-abc123
[debug] restoreKeys: [ 'Linux-node-' ]
[debug] Cache service URL: https://artifactcache.actions.githubusercontent.com/...
[debug] Request headers: Authorization: 'Bearer ***', Accept: 'application/json'
[debug] GET response: 404 (Not Found)
[debug] Trying restore key: Linux-node-
[debug] GET response: 200 OK
[debug] Cache found: cacheKey: 'Linux-node-def456', archiveLocation: 'https://...'
[debug] Downloading 234MB archive...
[debug] Extracting to /home/runner/work/repo/node_modules
Suddenly, you see why the wrong cache was restored (because the exact key failed, so it fell back to a prefix).
Let me know if you want me to add or change something.
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Debugging GitHub Actions Cache: A Practical Guide Caching is a powerful tool to speed up your CI/CD pipelines, but when it fails, it often does so silently. If your builds are suddenly slow or you're seeing inconsistent results, it’s time to debug your GitHub Actions cache Common Cache Issues Before diving into logs, check for these frequent pitfalls: Immutable Keys
: Once a cache is saved with a specific key, it cannot be updated. If your dependencies change but your key doesn't, you'll keep pulling old data. Branch Scoping
: Caches are scoped by branch. A cache created on a feature branch isn't available to other feature branches, though they can all access the default branch's cache. Job Success Requirement actions/cache
step only saves the cache if the entire job finishes successfully. Step-by-Step Debugging 1. Enable Step Debug Logging
To see exactly what the cache action is doing—including the resolved keys and download attempts—enable debug logging in GitHub Actions Navigate to your repository Secrets and variables Add a new repository variable: ACTIONS_STEP_DEBUG with the value Re-run your workflow. You will now see detailed messages in the logs. 2. Verify Your Cache Key Ensure your
function is actually detecting changes. You can add a temporary step to print the hash to the console: : Debug Cache Key "The hash is $ hashFiles('**/package-lock.json') " Use code with caution. Copied to clipboard
If the hash doesn't change when you update dependencies, the cache won't invalidate. 3. Inspect Cache Contents Locally Sometimes "cache hit: true" doesn't mean the files were restored. You can use the GitHub CLI gh-actions-cache extension
to list and even delete problematic caches from your terminal. 4. Live Debugging on the Runner debug-action-cache
For deep issues (like file permissions or path mismatches), use a tool like Action-Debugger
to SSH into the runner while it's paused. This lets you manually check if the files exist in the expected directory after the restore step. Quick Fix Checklist
Caching not working · community · Discussion #163260 - GitHub
To debug cache issues in GitHub Actions (specifically when using actions/cache), you should focus on verifying cache hits/misses, inspecting key generation, and enabling verbose logging. 1. Enable Verbose Debug Logging
The most effective way to see exactly what the cache action is doing—such as why a key didn't match or where it’s looking for files—is to enable debug mode for your runner.
Set Secrets: In your GitHub repository, go to Settings > Secrets and variables > Actions and add the following as repository secrets:
ACTIONS_STEP_DEBUG: Set to true to see detailed step output.
ACTIONS_CACHE_DEBUG: Set to true for specific, deep technical logs related to cache upload/download. 2. Verify Cache Hits and Misses in Logs
Check the Actions tab for your workflow run. Expand the "Post" or "Restore" steps for the cache to see the status: Success: You will see Cache restored from key: .
Failure (Miss): You will see Cache not found for input keys: .
Potential Issue: If you see Cache restored... but your build is still slow, your path might be incorrect, or the files are being overwritten by your build tool. 3. Inspect and Manage Caches via UI
GitHub provides a management interface to see what is currently stored: Navigate to your repository on GitHub. Click the Actions tab. In the left sidebar, under Management, click Caches.
Action: Here you can see cache sizes, last used dates, and delete problematic caches to force a fresh rebuild. 4. Common Troubleshooting Scenarios
Invalid Cache Keys: If your cache never hits, ensure your hashFiles function is pointing to the correct dependency file (e.g., package-lock.json or go.sum). Use key: $ runner.os -build-$ hashFiles('**/package-lock.json') to ensure the cache invalidates only when dependencies change.
Path Mismatches: Ensure the path you are caching actually exists. For example, pip cache is often in a different location than your project folder; use commands like pip cache dir to find the exact path. A normal log says: Cache restored from key:
Cross-OS Issues: Caches are typically isolated by operating system. A cache created on ubuntu-latest will not be available for a windows-latest runner.
Branch Isolation: Caches are isolated by branch. A PR branch can access the main branch cache, but the main branch cannot access caches created in a PR branch. 5. Debugging Tools & Extensions
tmate: Use the mxschmitt/action-tmate action to pause your workflow and SSH into the runner. This allows you to manually check if the files were actually restored to the directory you expected.
Local Testing: Use tools like nektos/act or the GitHub Local Actions VS Code extension to run your workflows locally and test cache logic without waiting for cloud runners.
Are you running into a specific error message, or is the cache simply not restoring as expected? Debug Github Actions - Daniela Baron
Unlocking Efficiency: A Deep Dive into Debug Action Cache
In the realm of software development, speed and efficiency are paramount. As developers, we're constantly seeking ways to streamline our workflows, reduce redundant tasks, and get our code to market faster. One often-overlooked yet powerful tool in achieving this goal is the Debug Action Cache. In this write-up, we'll explore the ins and outs of Debug Action Cache, its benefits, and how it can revolutionize your development process.
What is Debug Action Cache?
Debug Action Cache is a feature designed to cache the results of expensive computations or operations in your codebase. When you run your program or execute a specific action, the cache stores the output of that operation, so the next time you need to perform the same action, it can retrieve the result directly from the cache instead of recalculating it. This approach significantly reduces computation time, especially during debugging sessions.
How Does Debug Action Cache Work?
The Debug Action Cache operates on a simple yet effective principle:
Benefits of Debug Action Cache
The advantages of using Debug Action Cache are numerous:
Use Cases for Debug Action Cache
Best Practices for Implementing Debug Action Cache Suddenly, you see why the wrong cache was
To get the most out of Debug Action Cache:
Conclusion
Debug Action Cache is a powerful tool that can significantly enhance your development workflow. By understanding how it works and applying best practices, you can unlock substantial performance gains, reduce computation time, and increase productivity. Whether you're a developer, QA engineer, or DevOps professional, integrating Debug Action Cache into your toolkit can have a profound impact on your daily work. Give it a try and experience the benefits firsthand!
Don't wait for the cache to break. Create a dedicated "Cache Debug" workflow in your repo (.github/workflows/cache-debug.yml):
name: Cache Debugon: workflow_dispatch: inputs: debug_level: description: 'Debug level' default: 'full' type: choice options: ['full', 'basic']
jobs: debug-cache: runs-on: ubuntu-latest env: ACTIONS_STEP_DEBUG: $ 'false' ACTIONS_RUNNER_DEBUG: $ 'false' steps: - uses: actions/checkout@v4
- name: Generate cache key simulation id: sim run: | echo "hash=$(sha256sum package-lock.json | cut -d' ' -f1)" >> $GITHUB_OUTPUT - name: Attempt Cache Restore with Full Debug uses: actions/cache@v4 with: path: node_modules key: debug-$ runner.os -$ steps.sim.outputs.hash restore-keys: debug-$ runner.os - - name: Manual inspection run: | echo "=== CACHE DEBUG REPORT ===" echo "Node modules exist? $([ -d node_modules ] && echo 'YES' || echo 'NO')" echo "Count: $(find node_modules -type f 2>/dev/null | wc -l)"
Run this manually whenever you suspect cache rot. The env block forces debug-action-cache output into the logs.
Create a short, plain-text explanation of the term "debug-action-cache".
debug-action-cache: a mechanism used during software builds or CI workflows that records, reuses, and restores intermediate results of actions (like compiled objects, downloaded dependencies, or test outputs) so repeated runs skip already-completed steps, speeding up incremental builds and reducing network/compute usage. It typically keys cached items by action inputs (source files, environment, tool versions) and invalidates entries when inputs change.
The cache action creates a .tar archive. Debug logs reveal segmentation:
[debug] Compressing 1,234 files (245MB)
[debug] Archive segmented into 3 parts
[debug] Uploading part 1/3...
If you see a segmentation error (e.g., Part 2 failed to upload), you have a network issue or a file that changed during compression (race condition).
Add this to your workflow before the cache step:
env:
ACTIONS_RUNNER_DEBUG: true
ACTIONS_STEP_DEBUG: true
Now the cache action prints: