make this benchmark memory efficient

internal/collection/fields_test.go

@@ -1,6 +1,8 @@
 package collection
 
 import (
+	"fmt"
+	"math"
 	"math/rand"
 	"strconv"
 	"testing"
@@ -9,7 +11,6 @@ import (
 )
 
 type fieldobject struct {
-	id          string
 	fieldNames  []string
 	fieldValues []float64
 }
@@ -20,15 +21,11 @@ func BenchmarkItemFields(b *testing.B) {
 	var coll *Collection = New()
 
 	var k int = 100
+	var fillRatio float64 = 0.1
 
-	// Generate k fields, mapping to probability p.
-	var fields map[string]float64 = make(map[string]float64, k)
-	for i := 0; i < k; i++ {
-		field := strconv.Itoa(i)
-		prob := rand.Float64()
-
-		fields[field] = prob
-	}
+	// We have k fields, which will be filled with probability fillRatio.
+	// They are just 0...k-1 in string form so we don't actually need to
+	// map them.
 
 	// Generate n objects, just points.
 	json := `{"type":"Point","coordinates":[190,90]}`
@@ -37,34 +34,40 @@ func BenchmarkItemFields(b *testing.B) {
 		b.Fatal(err)
 	}
 
-	var objs []fieldobject
+	var objs []fieldobject = make([]fieldobject, b.N)
 
 	for i := 0; i < b.N; i++ {
-		var obj string = strconv.Itoa(i)
-
 		// set fields
-		var fieldNames []string
-		var values []float64
-		for field, prob := range fields {
-			if rand.Float64() > prob {
-				continue
-			}
+		var numFields int = int(math.Floor(float64(k) * fillRatio))
 
-			fieldNames = append(fieldNames, field)
-			values = append(values, 1.0)
+		var fieldNames []string = make([]string, numFields)
+		var values []float64 = make([]float64, numFields)
+
+		// set random fields at a random position.
+		// so start at a random position inside k, then increment so long
+		// as j is less than numFields. take the modulo to find insert position.
+		var start int = int(math.Floor(rand.Float64() * float64(k)))
+		for j := 0; j < numFields; j++ {
+			fieldNames[j] = strconv.Itoa((start + j) % k)
+			values[j] = 1.0
 		}
 
-		objs = append(objs, fieldobject{
-			id:          obj,
+		objs[i] = fieldobject{
 			fieldNames:  fieldNames,
 			fieldValues: values,
-		})
+		}
 	}
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		obj := objs[i]
 
-		coll.Set(obj.id, pt, obj.fieldNames, obj.fieldValues)
+		coll.Set(strconv.Itoa(i), pt, obj.fieldNames, obj.fieldValues)
 	}
+	b.StopTimer()
+
+	// Print out the memory usage of the first object.
+	bytesUsed := coll.TotalWeight()
+	fmt.Printf("%d bytes used, %f bytes per object, %f bytes per object per field\n",
+		bytesUsed, float64(bytesUsed) / float64(b.N), float64(bytesUsed) / (float64(b.N * k) * fillRatio))
 }