Troubleshooting Slow GitHub Actions Cache Uploads: A Key Engineering Productivity Metric

In the fast-paced world of software development, efficient CI/CD pipelines are crucial for maintaining high engineering productivity metrics. When a core component like caching slows down, it can significantly impact development cycles and project timelines. A recent discussion on the GitHub Community forum highlighted just such an issue, with users experiencing frustratingly slow GitHub Actions cache uploads.

The Problem: Suddenly Slow GitHub Actions Cache Uploads

User razvanz initiated a discussion titled "Why are cache uploads slow?" noting a drastic increase in cache upload times. What previously took around 1 minute at the beginning of January had ballooned to over 5 minutes. This slowdown occurred despite attempts to clear the cache, suggesting the issue wasn't related to slow evictions. The user suspected potential throttling and provided a log snippet demonstrating the erratic upload speeds:

Sent 0 of 1015506426 (0.0%), 0.0 MBs/sec
Sent 0 of 1015506426 (0.0%), 0.0 MBs/sec
Sent 469762048 of 1015506426 (46.3%), 149.2 MBs/sec
Sent 805306368 of 1015506426 (79.3%), 191.9 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 180.8 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 150.6 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 129.1 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 113.0 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 100.4 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 90.4 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 82.2 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 69.5 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 50.2 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 41.1 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 30.1 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 20.1 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 15.1 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 10.0 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 8.0 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 5.9 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 5.0 MBs/sec
Sent 948397562 of 1015506426 (93.4%), 3.2 MBs/sec
Sent 1015506426 of 1015506426 (100.0%), 3.4 MBs/sec

Expert Analysis: Why Cache Uploads Stall

Community expert DavitEgoian weighed in, offering two primary explanations for the observed behavior, particularly the stalling at 93.4% and the subsequent speed drop:

• Network Retries: The most common cause for such stalls is a failure to upload a specific "chunk" of the cache, leading the action to repeatedly retry sending it. This continuous retrying causes the average reported speed to decline significantly.
• Backend Throttling: GitHub Actions cache often leverages backend storage solutions like Azure Blob Storage. During periods of heavy load in a particular region, the storage backend might throttle requests. This can happen even if your specific repository isn't hitting an explicit rate limit, affecting overall GitHub metrics related to build times.

Actionable Solutions to Improve Your GitHub Metrics

To diagnose and potentially resolve slow cache uploads, DavitEgoian recommended several practical steps:

• Update the Action: Ensure your workflows are using actions/cache@v4. This newer version includes improvements in compression and upload handling, which can mitigate some performance issues.
• Enable Debug Logs: By setting the repository secret ACTIONS_STEP_DEBUG to true, you can enable verbose logging for your workflows. Rerunning the workflow with debug logs might reveal specific HTTP errors (e.g., 503 or 504) that pinpoint server-side problems or network issues.
• Check GitHub Status: Since the problem appeared suddenly, it could be linked to a regional service degradation. Regularly checking the GitHub Status page can provide insights into ongoing incidents that might affect cache performance.
• Open a Support Ticket: If the issue persists for more than a day or two, especially after trying the above steps, it's advisable to open a ticket with GitHub Support. They can investigate regional infrastructure issues or specific account-related throttling that might be impacting your software project dashboard's build efficiency.

Addressing slow cache uploads is vital for maintaining optimal engineering productivity metrics and ensuring smooth CI/CD operations. By following these diagnostic and resolution steps, developers can work towards more reliable and faster GitHub Actions workflows, ultimately contributing to a healthier software project dashboard.