What causes "mismatched cutoff and label lengths" in vitessio/vitess?

Make len(labels) == len(cutoffs)+1, with the last label the overflow bucket (commonly "unlimited").

mismatched cutoff and label lengths

Error message

mismatched cutoff and label lengths

What it means

NewGenericHistogram requires the labels slice to be exactly one longer than the cutoffs slice: one label per cutoff bucket plus a final label that captures everything above the highest cutoff. The library panics immediately when the counts do not satisfy this invariant.

Source

Thrown at go/stats/histogram.go:61

// based on the cutoffs. The buckets are categorized using the
// following criterion: cutoff[i-1] < value <= cutoff[i]. Anything
// higher than the highest cutoff is labeled as "inf".
func NewHistogram(name, help string, cutoffs []int64) *Histogram {
	labels := make([]string, len(cutoffs)+1)
	for i, v := range cutoffs {
		labels[i] = strconv.FormatInt(v, 10)
	}
	labels[len(labels)-1] = "inf"
	return NewGenericHistogram(name, help, cutoffs, labels, "Count", "Total")
}

// NewGenericHistogram creates a histogram where all the labels are
// supplied by the caller. The number of labels has to be one more than
// the number of cutoffs because the last label captures everything that
// exceeds the highest cutoff.
func NewGenericHistogram(name, help string, cutoffs []int64, labels []string, countLabel, totalLabel string) *Histogram {
	if len(cutoffs) != len(labels)-1 {
		panic("mismatched cutoff and label lengths")
	}
	h := &Histogram{
		name:       name,
		help:       help,
		cutoffs:    cutoffs,
		labels:     labels,
		countLabel: countLabel,
		totalLabel: totalLabel,
		buckets:    make([]atomic.Int64, len(labels)),
	}
	if name != "" {
		publish(name, h)
	}
	return h
}

// Adds a hook that will be called every time a new value is added to the histogram
func (h *Histogram) AddHook(hook func(int64)) {

View on GitHub (pinned to 01a25a7d17)

Solutions

Make len(labels) == len(cutoffs)+1, with the last label the overflow bucket (commonly "unlimited").
Recount the arrays at the call site; ensure every new cutoff gets a matching label plus keep the final catch-all label.
Define cutoffs and labels together as a single paired constant/slice to avoid drift.

Example fix

// before
cutoffs := []int64{1, 10, 100}
labels := []string{"0-1", "1-10", "10-100"} // panics: missing catch-all
// after
labels := []string{"0-1", "1-10", "10-100", "unlimited"}

Defensive patterns

Strategy: validation

Validate before calling

if len(labels) != len(cutoffs)+1 {
    return fmt.Errorf("histogram %s: need %d labels, got %d", name, len(cutoffs)+1, len(labels))
}
h := stats.NewGenericHistogram(name, help, cutoffs, labels, countLabel, totalLabel)

Prevention

Define cutoffs and the trailing catch-all label together in one constant block.
Include the overflow label (e.g. "unlimited") whenever you add a cutoff.
Add a package-level test asserting label count for every predefined histogram.

When it happens

Trigger: Calling stats.NewGenericHistogram(name, help, cutoffs, labels, ...) with len(cutoffs) != len(labels)-1, e.g. 4 cutoffs with 4 or 6 labels.

Common situations: Hand-editing a cutoffs list without updating labels; generating labels programmatically and off-by-one; copying a predefined label set but trimming the catch-all last label.

Related errors

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/f01032aaefa221cc. Report an issue: GitHub.