From 67a2e881af707f71ba75763552a12977c5efe12f Mon Sep 17 00:00:00 2001
From: Pedro Tanaka <pedro.tanaka@shopify.com>
Date: Thu, 5 Dec 2024 11:23:53 +0100
Subject: [PATCH] improve metrics

Signed-off-by: Pedro Tanaka <pedro.tanaka@shopify.com>
---
 pkg/store/storepb/matcher_cache.go      | 19 ++++++++++++++--
 pkg/store/storepb/matcher_cache_test.go | 29 +++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/pkg/store/storepb/matcher_cache.go b/pkg/store/storepb/matcher_cache.go
index c1a77ba061..5d77d73711 100644
--- a/pkg/store/storepb/matcher_cache.go
+++ b/pkg/store/storepb/matcher_cache.go
@@ -17,7 +17,7 @@ type NewItemFunc func(matcher LabelMatcher) (*labels.Matcher, error)
 
 type MatchersCache struct {
 	reg     prometheus.Registerer
-	cache   *lru.TwoQueueCache[LabelMatcher, *labels.Matcher]
+	cache   *lru.Cache[LabelMatcher, *labels.Matcher]
 	metrics *matcherCacheMetrics
 	size    int
 	sf      singleflight.Group
@@ -48,7 +48,7 @@ func NewMatchersCache(opts ...MatcherCacheOption) (*MatchersCache, error) {
 	}
 	cache.metrics = newMatcherCacheMetrics(cache.reg)
 
-	lruCache, err := lru.New2Q[LabelMatcher, *labels.Matcher](cache.size)
+	lruCache, err := lru.NewWithEvict[LabelMatcher, *labels.Matcher](cache.size, cache.onEvict)
 	if err != nil {
 		return nil, err
 	}
@@ -85,10 +85,17 @@ func (c *MatchersCache) GetOrSet(key LabelMatcher, newItem NewItemFunc) (*labels
 	return v.(*labels.Matcher), nil
 }
 
+func (c *MatchersCache) onEvict(_ LabelMatcher, _ *labels.Matcher) {
+	c.metrics.evicted.Inc()
+	c.metrics.numItems.Set(float64(c.cache.Len()))
+}
+
 type matcherCacheMetrics struct {
 	requestsTotal prometheus.Counter
 	hitsTotal     prometheus.Counter
 	numItems      prometheus.Gauge
+	maxItems      prometheus.Gauge
+	evicted       prometheus.Counter
 }
 
 func newMatcherCacheMetrics(reg prometheus.Registerer) *matcherCacheMetrics {
@@ -105,5 +112,13 @@ func newMatcherCacheMetrics(reg prometheus.Registerer) *matcherCacheMetrics {
 			Name: "thanos_matchers_cache_items",
 			Help: "Total number of cached items",
 		}),
+		maxItems: promauto.With(reg).NewGauge(prometheus.GaugeOpts{
+			Name: "thanos_matchers_cache_max_items",
+			Help: "Maximum number of items that can be cached",
+		}),
+		evicted: promauto.With(reg).NewCounter(prometheus.CounterOpts{
+			Name: "thanos_matchers_cache_evicted_total",
+			Help: "Total number of items evicted from the cache",
+		}),
 	}
 }
diff --git a/pkg/store/storepb/matcher_cache_test.go b/pkg/store/storepb/matcher_cache_test.go
index 754379474c..c76b942ae5 100644
--- a/pkg/store/storepb/matcher_cache_test.go
+++ b/pkg/store/storepb/matcher_cache_test.go
@@ -84,3 +84,32 @@ func TestMatchersCache(t *testing.T) {
 	testutil.Equals(t, false, cacheHit)
 	testutil.Equals(t, expected2.String(), item.String())
 }
+
+func BenchmarkMatchersCache(b *testing.B) {
+	cache, err := storepb.NewMatchersCache(storepb.WithSize(100))
+	if err != nil {
+		b.Fatalf("failed to create cache: %v", err)
+	}
+
+	matchers := []storepb.LabelMatcher{
+		{Type: storepb.LabelMatcher_EQ, Name: "key1", Value: "val1"},
+		{Type: storepb.LabelMatcher_EQ, Name: "key2", Value: "val2"},
+		{Type: storepb.LabelMatcher_EQ, Name: "key3", Value: "val3"},
+		{Type: storepb.LabelMatcher_EQ, Name: "key4", Value: "val4"},
+		{Type: storepb.LabelMatcher_RE, Name: "key5", Value: "^(val5|val6|val7|val8|val9).*$"},
+	}
+
+	newItem := func(matcher storepb.LabelMatcher) (*labels.Matcher, error) {
+		return storepb.MatcherToPromMatcher(matcher)
+	}
+
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		matcher := matchers[i%len(matchers)]
+		_, err := cache.GetOrSet(matcher, newItem)
+		if err != nil {
+			b.Fatalf("failed to get or set cache item: %v", err)
+		}
+	}
+}