cache: failed to reload key %q after eviction failure: %w

Error message

cache: failed to reload key %q after eviction failure: %w

What it means

Raised by refreshHeapIndex during the eviction-rollback path: a candidate evicted from the in-memory heap must be re-read from Storage to restore its heap index, and manager.get returned an error that is not errCacheMiss (a real backend failure). This indicates the external Storage (Redis, SQLite, etc.) is misbehaving in the middle of cache bookkeeping recovery, so the heap index for that key could not be re-established.

Source

Thrown at middleware/cache/cache.go:188

			return
		}

		entry := heap.entries[indexedIdx]
		if entry.idx != heapIdx || entry.key != entryKey {
			return
		}

		_, size := heap.remove(heapIdx)
		storedBytes -= size
	}

	refreshHeapIndex := func(ctx context.Context, candidate evictionCandidate) error {
		entry, err := manager.get(ctx, candidate.key)
		if err != nil {
			if errors.Is(err, errCacheMiss) {
				return nil
			}
			return fmt.Errorf("cache: failed to reload key %q after eviction failure: %w", maskKey(candidate.key), err)
		}

		entry.heapidx = candidate.heapIdx

		remainingTTL := max(secondsToTime(entry.exp).Sub(cfg.now()), 0)

		if err := manager.set(ctx, candidate.key, entry, remainingTTL); err != nil {
			return fmt.Errorf("cache: failed to restore heap index for key %q: %w", maskKey(candidate.key), err)
		}

		return nil
	}

	// Return new handler
	return func(c fiber.Ctx) error {
		hasAuthorization := len(c.Request().Header.Peek(fiber.HeaderAuthorization)) > 0
		reqCacheControl := c.Request().Header.Peek(fiber.HeaderCacheControl)
		reqDirectives := parseRequestCacheControl(reqCacheControl)

View on GitHub (pinned to 9a4c7e57fe)

Solutions

Check the health/latency of the configured cfg.Storage backend and its connection pool sizing.
Raise cfg.MaxBytes (or set it to 0 for unbounded) to reduce eviction churn that triggers the rollback path.
Ensure the storage driver is the one Fiber expects (correct version, compatible serialization) — a stale manager encoding can cause get errors.
If errors are transient, treat as best-effort: the entry remains in storage but loses heap-based expiration tracking; consider periodic cache flush or restart under sustained failures.

Example fix

// before: tiny MaxBytes + flaky redis -> eviction recovery fails on get
cache.New(cache.Config{
  Storage:  redisStorage,
  MaxBytes: 1 << 16,
})

// after: larger budget + tuned redis pool
cache.New(cache.Config{
  Storage:  redisStorage, // pool tuned for concurrency
  MaxBytes: 1 << 24,
  Expiration: 10 * time.Minute,
})

Defensive patterns

Strategy: try-catch

Validate before calling

// Health-check the cache storage before serving traffic.
func pingStorage(s fiber.Storage) error {
    ctx, cancel := context.WithTimeout(context.Background(), time.Second)
    defer cancel()
    return s.Set(ctx, "__ping__", []byte("1"), 5*time.Second)
}

Type guard

null

Try / catch

// Cache middleware returns the error from c.Next() chain; handle at app root.
app := fiber.New()
app.Use(cache.New(cfg))
app.Use(func(c fiber.Ctx) error {
    err := c.Next()
    if err != nil && strings.Contains(err.Error(), "failed to reload key") {
        // log storage degradation but don't crash the request
        log.Warnf("cache storage degraded: %v", err)
        return nil // or a 5xx with backoff
    }
    return err
})

Prevention

Tune the storage driver's connection pool and timeouts for expected load.
Raise cfg.MaxBytes to reduce eviction churn that triggers the rollback path.
Monitor storage latency/errors; alert before they reach the cache hot path.
Keep the storage driver version compatible with Fiber's manager encoding.

When it happens

Trigger: cfg.Storage is a remote backend (e.g. redis, leveldb) and an eviction delete failed, triggering restore; during restore, manager.get(candidate.key) hits a connection error, timeout, or deserialization error from the storage driver. Reproducible by forcing storage errors (mock/intercept) during concurrent cache writes that cross the MaxBytes boundary.

Common situations: Redis briefly drops the connection mid-request; storage responses larger than the msgp limit; TLS to the storage backend expired; storage pool exhausted under load; network partition while MaxBytes eviction churn is high.

Related errors

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/763130c48f4fdd67.json. Report an issue: GitHub.