Bazel is renowned for its speed, largely due to its advanced caching mechanisms, particularly the . By caching the output of every build step (action) based on its inputs, Bazel avoids redundant work, providing near-instant builds for minor changes. However, when Bazel decides an action is "dirty" and must be re-executed, it results in a cache miss, slowing down your pipeline.
To debug an action cache effectively, a developer must move from guessing to empirical comparison.
- name: Cache Node Modules uses: actions/cache@v3 with: path: node_modules key: $ runner.os -node-$ hashFiles('package-lock.json') restore-keys: | $ runner.os -node-
- name: Generate cache key simulation id: sim run: | echo "hash=$(sha256sum package-lock.json | cut -d' ' -f1)" >> $GITHUB_OUTPUT
Prevent untrusted or experimental PR code from overwriting the main branch's cache. Only allow the default branch ( main / master ) to write to the cache. debug-action-cache
: If you require that the cache always be saved, you must abandon the all-in-one actions/cache action and use the more granular restore and save actions separately. By splitting the logic, you can control the save step with an if: always() condition to ensure it executes regardless of prior failures.
Before you can debug a cache problem, you must first understand the engine behind it. The actions/cache action is designed to speed up workflows by storing and reusing dependencies or build outputs. Because GitHub-hosted runners start in a clean virtual environment for each job, caching prevents you from having to download the same packages and tools repeatedly.
GitHub Actions has a built-in mechanism to increase log verbosity.
Sometimes, actions are intentionally excluded from caching. Look at the progress_message in the execution log and ensure cacheable is not set to false due to tags=["no-cache"] in your BUILD files 2.2.3. 4. Debugging Remote Cache Hits Bazel is renowned for its speed, largely due
Navigate to your GitHub repository and click on > Caches (located in the left sidebar). This dashboard provides critical forensic data:
The debug logs will show you precisely which paths were checked and why they were not found.
The standard cache action works on three principles:
Throughout the rest of this article, we will explore each of these steps in painstaking detail. To debug an action cache effectively, a developer
To minimize the need for intense debugging sessions, construct your cache architecture using defensive engineering practices:
:
The first step is determining why a cache miss occurred when a hit was expected. Most modern build tools provide execution logs or "cache-miss" reports. By comparing the hash of a local action against the hash stored in the cache, developers can identify the specific file or environment variable that caused the discrepancy.