Add optional index metrics.

cache.go

@@ -65,7 +65,7 @@ type LRUCache struct {
 	metrics *CacheMetrics
 }
 
-// WithCacheMetrics is an option for LRUCache to set a CacheMetrics option.
+// WithCacheMetrics is an option for LRUCache to set a CacheMetrics object.
 func WithCacheMetrics(metrics *CacheMetrics) LRUCacheOption {
 	return func(c *LRUCache) {
 		c.metrics = metrics

index.go

@@ -51,6 +51,7 @@ func OpenIndexFromBoltDatabase(db *bbolt.DB, opts ...IndexOption) (*Index, error
 	}
 
 	idx.cache = &nullCache{}
+	idx.metrics = &IndexMetrics{}
 
 	for _, opt := range opts {
 		if err := opt(idx); err != nil {
@@ -77,7 +78,8 @@ type Index struct {
 
 	values colGetter
 
-	cache Cache
+	cache   Cache
+	metrics *IndexMetrics
 }
 
 type colGetter interface {
@@ -158,6 +160,23 @@ func WithPreloadedData() IndexOption {
 	}
 }
 
+// WithIndexMetrics is an option for OpenIndex and OpenIndexFromBoltDatabase to set
+// an IndexMetrics object.
+func WithIndexMetrics(metrics *IndexMetrics) IndexOption {
+	return func(c *Index) error {
+		c.metrics = metrics
+		return nil
+	}
+}
+
+type IndexMetrics struct {
+	ExecuteDuration HistogramMetric
+}
+
+type HistogramMetric interface {
+	Observe(float64)
+}
+
 func newPreloadedColGetter(db *bbolt.DB) (colGetter, error) {
 	cg := &preloadedColGetter{
 		values: map[uint64]*roaring.Bitmap{},

query.go

@@ -5,6 +5,7 @@ import (
 	"math/bits"
 	"sort"
 	"strings"
+	"time"
 
 	"github.com/RoaringBitmap/roaring"
 )
@@ -24,8 +25,14 @@ type Query struct {
 	groupByFields []groupBy
 }
 
-// Execute runs the query on the provided index and returns the query result.
-func (q *Query) Execute(idx *Index) (*Result, error) {
+// Execute runs the provided query on the index and returns the query result.
+func (idx *Index) Execute(q *Query) (*Result, error) {
+	if idx.metrics.ExecuteDuration != nil {
+		defer func(t0 time.Time) {
+			idx.metrics.ExecuteDuration.Observe(time.Since(t0).Seconds())
+		}(time.Now())
+	}
+
 	idx.mtx.RLock()
 	defer idx.mtx.RUnlock()
 

query_test.go

@@ -135,7 +135,7 @@ func TestQuery(t *testing.T) {
 		for _, tt := range testData {
 			t.Run(tt.name, func(t *testing.T) {
 				t.Logf("query = %s", tt.query.Expr.String())
-				result, err := tt.query.Execute(idx)
+				result, err := idx.Execute(tt.query)
 				require.NoError(t, err)
 				require.NotNil(t, result)
 				require.Equal(t, tt.expectedResult, result.Count)
@@ -333,7 +333,7 @@ func TestQueryGroupBy(t *testing.T) {
 
 	for _, tt := range testData {
 		t.Run(tt.name, func(t *testing.T) {
-			result, err := tt.query.Execute(idx)
+			result, err := idx.Execute(tt.query)
 			require.NoError(t, err)
 			require.NotNil(t, result)
 			require.Equal(t, tt.expectedResult, result)
@@ -431,7 +431,7 @@ func runBenchmarkQuery(b *testing.B, idx *Index) {
 			GroupBy: []string{"is_cool"},
 		}
 
-		_, err := q.Execute(idx)
+		_, err := idx.Execute(q)
 		require.NoError(b, err)
 	}
 }