Slight improvements to `GetFactorOfTime` (#9473)

* correctly returns zero for non-overlapping data
* adds tests

pkg/querier/queryrange/index_stats_cache.go

@@ -27,7 +27,7 @@ type IndexStatsExtractor struct{}
 // Extract favors the ability to cache over exactness of results. It assumes a constant distribution
 // of log volumes over a range and will extract subsets proportionally.
 func (p IndexStatsExtractor) Extract(start, end int64, res queryrangebase.Response, resStart, resEnd int64) queryrangebase.Response {
-	factor, _, _ := util.GetFactorOfTime(start, end, resStart, resEnd)
+	factor := util.GetFactorOfTime(start, end, resStart, resEnd)
 
 	statsRes := res.(*IndexStatsResponse)
 	return &IndexStatsResponse{

pkg/util/time.go

@@ -128,11 +128,15 @@ func ForInterval(interval time.Duration, start, end time.Time, endTimeInclusive
 //
 // We get the percentage of time that fits into C
 // factor = C = (T - (A + B)) / T = (chunkTime - (leadingTime + trailingTime)) / chunkTime
-func GetFactorOfTime(from, through int64, minTime, maxTime int64) (factor float64, leadingTime, trailingTime int64) {
+func GetFactorOfTime(from, through int64, minTime, maxTime int64) (factor float64) {
+	if from > maxTime || through < minTime {
+		return 0
+	}
+
 	totalTime := maxTime - minTime
-	leadingTime = utilsMath.Max64(0, from-minTime)
-	trailingTime = utilsMath.Max64(0, maxTime-through)
+	leadingTime := utilsMath.Max64(0, from-minTime)
+	trailingTime := utilsMath.Max64(0, maxTime-through)
 	factor = float64(totalTime-(leadingTime+trailingTime)) / float64(totalTime)
 
-	return factor, leadingTime, trailingTime
+	return factor
 }

pkg/util/time_test.go

@@ -227,3 +227,53 @@ func TestForInterval(t *testing.T) {
 		})
 	}
 }
+
+func TestGetFactorOfTime(t *testing.T) {
+	for _, tc := range []struct {
+		desc                                string
+		from, through, extentMin, extentMax int64
+		exp                                 float64
+	}{
+		{
+			desc: "equal",
+			from: 10, through: 20,
+			extentMin: 10, extentMax: 20,
+			exp: 1,
+		},
+		{
+			desc: "50% overlap on left",
+			from: 10, through: 20,
+			extentMin: 5, extentMax: 15,
+			exp: 0.5,
+		},
+		{
+			desc: "50% overlap on right",
+			from: 10, through: 20,
+			extentMin: 15, extentMax: 25,
+			exp: 0.5,
+		},
+		{
+			desc: "10% overlap on right",
+			from: 15, through: 16,
+			extentMin: 15, extentMax: 25,
+			exp: 0.1,
+		},
+		{
+			desc: "no overlap",
+			from: 10, through: 20,
+			extentMin: 25, extentMax: 35,
+			exp: 0,
+		},
+		{
+			desc: "no overlap, through=extentMin",
+			from: 10, through: 20,
+			extentMin: 20, extentMax: 35,
+			exp: 0,
+		},
+	} {
+		t.Run(tc.desc, func(t *testing.T) {
+			factor := GetFactorOfTime(tc.from, tc.through, tc.extentMin, tc.extentMax)
+			require.Equal(t, tc.exp, factor)
+		})
+	}
+}