GitHub Actions "reserveCache failed: Cache size exceeds limit"

Before uploading, the cache client reserves space. The reservation fails if the entry exceeds the per-cache size limit or the repository has hit its total cache quota (caches are evicted by least-recently-used).

What this error means

The cache save step warns that reserveCache failed with a size or quota message; the cache is not saved.

Failed to save: reserveCache failed: Cache size of ~12000 MB (12582912000 B) is over the 10GB limit, not saving cache.
Warning: Cache save failed.

Common causes

Entry over the per-cache size limit

A single cache entry exceeds the 10 GB per-cache cap.

Repo cache quota exhausted

The repository total cache storage is full; old caches are evicted but a too-large new entry still fails.

How to fix it

Shrink what you cache

1. Cache only the package manager store, not entire build trees.
2. Exclude large generated artifacts from the cached path.
3. Split into multiple smaller caches if needed.

- uses: actions/cache@v4
  with:
    path: ~/.cache/pip
    key: pip-${{ hashFiles('**/requirements*.txt') }}

How to prevent it

• Keep cache entries well under the per-cache limit.
• Prune stale caches and avoid caching reproducible build output.

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