What causes "cache: failed to store key %q: %w" in gofiber/fiber?

Inspect the wrapped Storage error to identify the cause (capacity, network, auth).

cache: failed to store key

Error message

cache: failed to store key %q: %w

What it means

Returned by manager.set when the external Storage's SetWithContext fails after successful msgp serialization. The metadata entry could not be persisted; the item is released back to the pool and the cache write is aborted.

Solutions

Inspect the wrapped Storage error to identify the cause (capacity, network, auth).
Check backend memory/quota and eviction policy (Redis maxmemory-policy).
Increase write timeout and connection pool size if the error correlates with load.
Treat the cache as advisory: log and proceed uncached rather than failing the user request.

Example fix

// Cache writes are advisory — isolate them from the response path:
if err := manager.set(reqCtx, key, e, exp); err != nil {
    log.Warn("cache store failed; serving uncached:", err)
    // do NOT return err to the client; the handler result is still valid
}

Defensive patterns

Strategy: retry

Validate before calling

func storageWritable(ctx context.Context, s fiber.Storage) error {
    return s.SetWithContext(ctx, "__wprobe__", []byte("ok"), time.Second)
}

Try / catch

// Cache writes are advisory; isolate from the response path.
if err := manager.set(reqCtx, key, e, exp); err != nil {
    if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
        return // client gone
    }
    log.Warn("cache metadata store failed; serving uncached:", err)
}

Prevention

Treat cache store failures as non-fatal; log and continue.
Provision Storage capacity headroom and a permissive eviction policy.
Tune write timeouts to your Storage p99.

When it happens

Trigger: Cache store path (cfg.Storage set) where Storage.SetWithContext returns an error: backend down, write timeout, max-memory/quota exceeded on Redis, network error, context cancellation mid-write.

Common situations: Redis maxmemory eviction policies dropping writes, backend at capacity, network blips, TLS/auth mismatch, storage driver write timeouts too tight under load, client disconnect cancelling the request context.

Related errors

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/055abd1eaf03fdb9. Report an issue: GitHub.

Appendix: source

Thrown at middleware/cache/manager.go:174

			return nil, fmt.Errorf("cache: unexpected raw entry type %T for key %q", value, m.logKey(key))
		}
		return raw, nil
	}

	return nil, errCacheMiss
}

// set data to storage or memory
func (m *manager) set(ctx context.Context, key string, it *item, exp time.Duration) error {
	if m.storage != nil {
		raw, err := it.MarshalMsg(nil)
		if err != nil {
			m.release(it)
			return fmt.Errorf("cache: failed to marshal key %q: %w", m.logKey(key), err)
		}
		if err := m.storage.SetWithContext(ctx, key, raw, exp); err != nil {
			m.release(it)
			return fmt.Errorf("cache: failed to store key %q: %w", m.logKey(key), err)
		}
		m.release(it)
		return nil
	}

	m.memory.Set(key, it, exp)
	return nil
}

// set data to storage or memory
func (m *manager) setRaw(ctx context.Context, key string, raw []byte, exp time.Duration) error {
	if m.storage != nil {
		if err := m.storage.SetWithContext(ctx, key, raw, exp); err != nil {
			return fmt.Errorf("cache: failed to store raw key %q: %w", m.logKey(key), err)
		}
		return nil
	}

View on GitHub (pinned to a105acad6c)