{"record":{"id":"763130c48f4fdd67","repo":"gofiber/fiber","slug":"cache-failed-to-reload-key-q-after-eviction-fail","errorCode":null,"errorMessage":"cache: failed to reload key %q after eviction failure: %w","messagePattern":"cache: failed to reload key %q after eviction failure: %w","errorType":"http","errorClass":null,"httpStatus":500,"severity":"warning","filePath":"middleware/cache/cache.go","lineNumber":211,"sourceCode":"\t\t\treturn\n\t\t}\n\n\t\tentry := heap.entries[indexedIdx]\n\t\tif entry.idx != heapIdx || entry.key != entryKey {\n\t\t\treturn\n\t\t}\n\n\t\t_, size := heap.remove(heapIdx)\n\t\tstoredBytes -= size\n\t}\n\n\trefreshHeapIndex := func(ctx context.Context, candidate evictionCandidate) error {\n\t\tentry, err := manager.get(ctx, candidate.key)\n\t\tif err != nil {\n\t\t\tif errors.Is(err, errCacheMiss) {\n\t\t\t\treturn nil\n\t\t\t}\n\t\t\treturn fmt.Errorf(\"cache: failed to reload key %q after eviction failure: %w\", maskKey(candidate.key), err)\n\t\t}\n\n\t\tentry.heapidx = candidate.heapIdx\n\n\t\tremainingTTL := max(secondsToTime(entry.exp).Sub(cfg.now()), 0)\n\n\t\tif err := manager.set(ctx, candidate.key, entry, remainingTTL); err != nil {\n\t\t\treturn fmt.Errorf(\"cache: failed to restore heap index for key %q: %w\", maskKey(candidate.key), err)\n\t\t}\n\n\t\treturn nil\n\t}\n\n\t// Return new handler\n\treturn func(c fiber.Ctx) error {\n\t\t// Every field line, like the hash below: an empty first Authorization line\n\t\t// would otherwise read as anonymous. canonical is app config, fixed for the\n\t\t// life of the handler, so read it once.","sourceCodeStart":193,"sourceCodeEnd":229,"githubUrl":"https://github.com/gofiber/fiber/blob/a105acad6c1e4576a77f01e02973f67e962bb58d/middleware/cache/cache.go#L193-L229","documentation":"Returned by refreshHeapIndex inside the cache middleware when, during eviction rollback, manager.get fails to reload an entry that was being evicted. The cache keeps a min-heap of entries by expiry; when an eviction has to be undone, the entry is re-fetched. errCacheMiss is treated as benign (the key was concurrently deleted); any other storage error is wrapped here with the masked key.","triggerScenarios":"An external Redis/MySQL/storage backend used as cfg.Storage returns a transient error (connection reset, timeout, context cancellation) exactly when the cache tries to re-read an entry it had just selected for eviction. Concurrent expiration from another Fiber instance in a multi-node deployment can also remove the entry.","commonSituations":"Multi-instance Fiber deployment sharing a Redis storage with flaky networking; storage under memory pressure returning errors; a request whose context was canceled (client disconnect) reaching the eviction-rollback path; storage backend restarting mid-request.","solutions":["Investigate the wrapped storage error: it carries the backend's message.","Tighten storage health: connection pool sizing, timeouts, TLS to Redis/MySQL.","If multi-instance, expect occasional errCacheMiss and ensure they are filtered (they are here, but other backend errors are not).","Add storage instrumentation (latency, error rate) to catch the underlying cause.","Consider cfg.MaxBytes sizing so eviction storms are rare."],"exampleFix":"// before: shared Redis with no timeout, intermittent resets\ncfg := cache.Config{Storage: myRedis}\n\n// after: bounded Redis client with timeouts and pool caps\ncfg := cache.Config{Storage: rueidisWithTimeouts}","handlingStrategy":"try-catch","validationCode":"// Before enabling cache with shared storage, probe health.\nfunc probeStorage(s fiber.Storage) error {\n    ctx, cancel := context.WithTimeout(context.Background(), time.Second)\n    defer cancel()\n    if err := s.Set(\"fiber:health\", []byte(\"ok\"), time.Second); err != nil { return err }\n    _, err = s.Get(\"fiber:health\")\n    return err\n}","typeGuard":null,"tryCatchPattern":"// cache middleware surfaces storage errors via the configured error handler.\n// Add a recovery middleware that treats cache storage errors as non-fatal and serves a fresh (uncached) response.\napp.Use(func(c fiber.Ctx) error {\n    err := c.Next()\n    if err != nil {\n        if isCacheStorageErr(err) { // match the \"cache: \" prefix\n            _ = c.Response().Reset()\n            return nil // let downstream handlers re-run without cache\n        }\n    }\n    return err\n})","preventionTips":["Use a storage client with bounded dial/read/write timeouts.","Monitor storage error rate and latency as SLOs.","Size cfg.MaxBytes to avoid eviction storms amplifying storage blips.","In multi-instance setups, expect occasional errCacheMiss and rely on natural re-population."],"tags":["cache","storage","eviction","redis","distributed"],"backgroundTag":null,"analyzedSha":"a105acad6c1e4576a77f01e02973f67e962bb58d","analyzedAt":"2026-08-11T17:33:26.942Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}