max item size ( ) cannot be bigger than overall cache size…

Error message

max item size (%v) cannot be bigger than overall cache size (%v)

What it means

NewInMemoryIndexCacheWithConfig enforces that the maximum size of any single cached item does not exceed the overall byte budget of the in-memory LRU cache; otherwise every insert of a large item would immediately evict or never fit. It throws this error when config.MaxItemSize > config.MaxSize.

Solutions

Set max_size to a value >= max_item_size.
Lower max_item_size below max_size if the total budget is fixed.
Remove max_item_size to use its default (usually derived from max_size).

Example fix

// before
max_size: 100000000
max_item_size: 2147483648
// after
max_size: 2147483648
max_item_size: 1073741824

Defensive patterns

Strategy: validation

Validate before calling

if cfg.MaxItemSize > cfg.MaxSize {
	return fmt.Errorf("in-memory cache misconfigured: max_item_size (%d) must be <= max_size (%d)", cfg.MaxItemSize, cfg.MaxSize)
}

Try / catch

if _, err := storecache.NewInMemoryIndexCacheWithConfig(logger, nil, reg, cfg); err != nil {
	if strings.Contains(err.Error(), "cannot be bigger than overall cache size") {
		cfg.MaxItemSize = cfg.MaxSize / 2 // or fail fast
	}
	return err
}

Prevention

Assert max_item_size <= max_size in config tests.
Pick max_item_size as a fraction (e.g. 1/64) of max_size.
Keep both values in the same unit (bytes) in generated config.

When it happens

Trigger: Calling NewInMemoryIndexCache or NewInMemoryIndexCacheWithConfig with an InMemoryIndexCacheConfig where MaxItemSize bytes is greater than MaxSize bytes, e.g. max_size: 100MB with max_item_size: 500MB, or MaxItemSize set while MaxSize left small.

Common situations: Hand-tuning store-gateway index-cache limits and swapping the two values; setting max_item_size from a guide without raising max_size; unit confusion between bytes values in YAML config.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/f970915cce17bf36. Report an issue: GitHub.

Appendix: source

Thrown at pkg/store/cache/inmemory.go:94

	return config, nil
}

// NewInMemoryIndexCache creates a new thread-safe LRU cache for index entries and ensures the total cache
// size approximately does not exceed maxBytes.
func NewInMemoryIndexCache(logger log.Logger, commonMetrics *CommonMetrics, reg prometheus.Registerer, conf []byte) (*InMemoryIndexCache, error) {
	config, err := parseInMemoryIndexCacheConfig(conf)
	if err != nil {
		return nil, err
	}

	return NewInMemoryIndexCacheWithConfig(logger, commonMetrics, reg, config)
}

// NewInMemoryIndexCacheWithConfig creates a new thread-safe LRU cache for index entries and ensures the total cache
// size approximately does not exceed maxBytes.
func NewInMemoryIndexCacheWithConfig(logger log.Logger, commonMetrics *CommonMetrics, reg prometheus.Registerer, config InMemoryIndexCacheConfig) (*InMemoryIndexCache, error) {
	if config.MaxItemSize > config.MaxSize {
		return nil, errors.Errorf("max item size (%v) cannot be bigger than overall cache size (%v)", config.MaxItemSize, config.MaxSize)
	}

	if commonMetrics == nil {
		commonMetrics = NewCommonMetrics(reg)
	}

	c := &InMemoryIndexCache{
		logger:           logger,
		maxSizeBytes:     uint64(config.MaxSize),
		maxItemSizeBytes: uint64(config.MaxItemSize),
		commonMetrics:    commonMetrics,
	}

	c.evicted = promauto.With(reg).NewCounterVec(prometheus.CounterOpts{
		Name: "thanos_store_index_cache_items_evicted_total",
		Help: "Total number of items that were evicted from the index cache.",
	}, []string{"item_type"})
	c.evicted.WithLabelValues(CacheTypePostings)

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