Function labelValuesWithMatchers

tsdb/querier.go:464–535

(ctx context.Context, r IndexReader, name string, hints *storage.LabelHints, matchers ...*labels.Matcher)

}

func labelValuesWithMatchers(ctx context.Context, r IndexReader, name string, hints *storage.LabelHints, matchers ...*labels.Matcher) ([]string, error) {
	// Limit is applied at the end, after filtering.
	allValues, err := r.LabelValues(ctx, name, nil)
	if err != nil {
		return nil, fmt.Errorf("fetching values of label %s: %w", name, err)
	}

	// If we have a matcher for the label name, we can filter out values that don't match
	// before we fetch postings. This is especially useful for labels with many values.
	// e.g. __name__ with a selector like {__name__="xyz"}
	hasMatchersForOtherLabels := false
	for _, m := range matchers {
		if m.Name != name {
			hasMatchersForOtherLabels = true
			continue
		}

		// re-use the allValues slice to avoid allocations
		// this is safe because the iteration is always ahead of the append
		filteredValues := allValues[:0]
		count := 1
		for _, v := range allValues {
			if count%checkContextEveryNIterations == 0 && ctx.Err() != nil {
				return nil, ctx.Err()
			}
			count++
			if m.Matches(v) {
				filteredValues = append(filteredValues, v)
			}
		}
		allValues = filteredValues
	}

	if len(allValues) == 0 {
		return nil, nil
	}

	// If we don't have any matchers for other labels, then we're done.
	if !hasMatchersForOtherLabels {
		if hints != nil && hints.Limit > 0 && len(allValues) > hints.Limit {
			allValues = allValues[:hints.Limit]
		}
		return allValues, nil
	}

	p, err := PostingsForMatchers(ctx, r, matchers...)
	if err != nil {
		return nil, fmt.Errorf("fetching postings for matchers: %w", err)
	}

	valuesPostings := make([]index.Postings, len(allValues))
	for i, value := range allValues {
		valuesPostings[i], err = r.Postings(ctx, name, value)
		if err != nil {
			return nil, fmt.Errorf("fetching postings for %s=%q: %w", name, value, err)
		}
	}
	indexes, err := index.FindIntersectingPostings(p, valuesPostings)