feat: collect ristretto cache metrics helper (#834)

cachex/ristretto.go

@@ -0,0 +1,67 @@
+// Copyright © 2025 Ory Corp
+// SPDX-License-Identifier: Apache-2.0
+
+package cachex
+
+import (
+	"github.com/dgraph-io/ristretto"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// RistrettoCollector collects Ristretto cache metrics.
+type RistrettoCollector[K ristretto.Key, V any] struct {
+	prefix      string
+	metricsFunc func() *ristretto.Metrics
+}
+
+// NewRistrettoCollector creates a new RistrettoCollector.
+//
+// To use this collector, you need to register it with a Prometheus registry:
+//
+//	func main() {
+//		cache, _ := ristretto.NewCache(&ristretto.Config{
+//			NumCounters: 1e7,
+//			MaxCost:     1 << 30,
+//			BufferItems: 64,
+//		})
+//		collector := NewRistrettoCollector("prefix_", func() *ristretto.Metrics {
+//			return cache.Metrics
+//		})
+//		prometheus.MustRegister(collector)
+//	}
+func NewRistrettoCollector[K ristretto.Key, V any](prefix string, metricsFunc func() *ristretto.Metrics) *RistrettoCollector[K, V] {
+	return &RistrettoCollector[K, V]{
+		prefix:      prefix,
+		metricsFunc: metricsFunc,
+	}
+}
+
+// Describe sends the super-set of all possible descriptors of metrics
+// collected by this Collector.
+func (c *RistrettoCollector[K, V]) Describe(ch chan<- *prometheus.Desc) {
+	ch <- prometheus.NewDesc(c.prefix+"ristretto_hits", "Total number of cache hits", nil, nil)
+	ch <- prometheus.NewDesc(c.prefix+"ristretto_misses", "Total number of cache misses", nil, nil)
+	ch <- prometheus.NewDesc(c.prefix+"ristretto_ratio", "Cache hit ratio", nil, nil)
+	ch <- prometheus.NewDesc(c.prefix+"ristretto_keys_added", "Total number of keys added to the cache", nil, nil)
+	ch <- prometheus.NewDesc(c.prefix+"ristretto_cost_added", "Total cost of keys added to the cache", nil, nil)
+	ch <- prometheus.NewDesc(c.prefix+"ristretto_keys_evicted", "Total number of keys evicted from the cache", nil, nil)
+	ch <- prometheus.NewDesc(c.prefix+"ristretto_cost_evicted", "Total cost of keys evicted from the cache", nil, nil)
+	ch <- prometheus.NewDesc(c.prefix+"ristretto_sets_dropped", "Total number of sets dropped", nil, nil)
+	ch <- prometheus.NewDesc(c.prefix+"ristretto_sets_rejected", "Total number of sets rejected", nil, nil)
+	ch <- prometheus.NewDesc(c.prefix+"ristretto_gets_kept", "Total number of gets kept", nil, nil)
+}
+
+// Collect is called by the Prometheus registry when collecting metrics.
+func (c *RistrettoCollector[K, V]) Collect(ch chan<- prometheus.Metric) {
+	metrics := c.metricsFunc()
+	ch <- prometheus.MustNewConstMetric(prometheus.NewDesc(c.prefix+"ristretto_hits", "Total number of cache hits", nil, nil), prometheus.GaugeValue, float64(metrics.Hits()))
+	ch <- prometheus.MustNewConstMetric(prometheus.NewDesc(c.prefix+"ristretto_misses", "Total number of cache misses", nil, nil), prometheus.GaugeValue, float64(metrics.Misses()))
+	ch <- prometheus.MustNewConstMetric(prometheus.NewDesc(c.prefix+"ristretto_ratio", "Cache hit ratio", nil, nil), prometheus.GaugeValue, metrics.Ratio())
+	ch <- prometheus.MustNewConstMetric(prometheus.NewDesc(c.prefix+"ristretto_keys_added", "Total number of keys added to the cache", nil, nil), prometheus.GaugeValue, float64(metrics.KeysAdded()))
+	ch <- prometheus.MustNewConstMetric(prometheus.NewDesc(c.prefix+"ristretto_cost_added", "Total cost of keys added to the cache", nil, nil), prometheus.GaugeValue, float64(metrics.CostAdded()))
+	ch <- prometheus.MustNewConstMetric(prometheus.NewDesc(c.prefix+"ristretto_keys_evicted", "Total number of keys evicted from the cache", nil, nil), prometheus.GaugeValue, float64(metrics.KeysEvicted()))
+	ch <- prometheus.MustNewConstMetric(prometheus.NewDesc(c.prefix+"ristretto_cost_evicted", "Total cost of keys evicted from the cache", nil, nil), prometheus.GaugeValue, float64(metrics.CostEvicted()))
+	ch <- prometheus.MustNewConstMetric(prometheus.NewDesc(c.prefix+"ristretto_sets_dropped", "Total number of sets dropped", nil, nil), prometheus.GaugeValue, float64(metrics.SetsDropped()))
+	ch <- prometheus.MustNewConstMetric(prometheus.NewDesc(c.prefix+"ristretto_sets_rejected", "Total number of sets rejected", nil, nil), prometheus.GaugeValue, float64(metrics.SetsRejected()))
+	ch <- prometheus.MustNewConstMetric(prometheus.NewDesc(c.prefix+"ristretto_gets_kept", "Total number of gets kept", nil, nil), prometheus.GaugeValue, float64(metrics.GetsKept()))
+}