From 76707b2ab974e2b447d7bc6e916a88109ecff19d Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Sat, 4 Jan 2020 14:18:38 +0200
Subject: [PATCH] app/vmselect/promql: fix calculations for `histogram_share`

---
 app/vmselect/promql/exec_test.go |  4 ++--
 app/vmselect/promql/transform.go | 33 ++++++++++++++++----------------
 2 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/app/vmselect/promql/exec_test.go b/app/vmselect/promql/exec_test.go
index c1ecf4231f..c8dcfbc108 100644
--- a/app/vmselect/promql/exec_test.go
+++ b/app/vmselect/promql/exec_test.go
@@ -2686,14 +2686,14 @@ func TestExecSuccess(t *testing.T) {
 	})
 	t.Run(`histogram_share(normal-bucket-count)`, func(t *testing.T) {
 		t.Parallel()
-		q := `histogram_share(22,
+		q := `histogram_share(35,
 			label_set(0, "foo", "bar", "le", "10")
 			or label_set(100, "foo", "bar", "le", "30")
 			or label_set(300, "foo", "bar", "le", "+Inf")
 		)`
 		r := netstorage.Result{
 			MetricName: metricNameExpected,
-			Values:     []float64{0.2, 0.2, 0.2, 0.2, 0.2, 0.2},
+			Values:     []float64{0.3333333333333333, 0.3333333333333333, 0.3333333333333333, 0.3333333333333333, 0.3333333333333333, 0.3333333333333333},
 			Timestamps: timestampsExpected,
 		}
 		r.MetricName.Tags = []storage.Tag{{
diff --git a/app/vmselect/promql/transform.go b/app/vmselect/promql/transform.go
index 4931e13d54..35f0490b4f 100644
--- a/app/vmselect/promql/transform.go
+++ b/app/vmselect/promql/transform.go
@@ -440,29 +440,30 @@ func transformHistogramShare(tfa *transformFuncArg) ([]*timeseries, error) {
 		if math.IsInf(leReq, 1) {
 			return 1, 1, 1
 		}
-		for j, xs := range xss {
+		var vPrev, lePrev float64
+		for _, xs := range xss {
 			v := xs.ts.Values[i]
 			le := xs.le
-			if leReq < le {
+			if leReq >= le {
+				vPrev = v
+				lePrev = le
 				continue
 			}
-			// precondition: leReq >= le
-			if j+1 >= len(xss) {
-				return 1, 1, 1
-			}
-			vNext := xss[j+1].ts.Values[i]
-			leNext := xss[j+1].le
-			if math.IsInf(leNext, 1) {
-				return v / vNext, v / vNext, 1
-			}
+			// precondition: lePrev <= leReq < le
 			vLast := xss[len(xss)-1].ts.Values[i]
-			lower = v / vLast
-			upper = vNext / vLast
-			q = lower + (vNext-v)/vLast*(leReq-le)/(leNext-le)
+			lower = vPrev / vLast
+			if math.IsInf(le, 1) {
+				return lower, lower, 1
+			}
+			if lePrev == leReq {
+				return lower, lower, lower
+			}
+			upper = v / vLast
+			q = lower + (v-vPrev)/vLast*(leReq-lePrev)/(le-lePrev)
 			return q, lower, upper
 		}
-		leLast := xss[len(xss)-1].le
-		return leReq / leLast, 0, 1
+		// precondition: leReq > leLast
+		return 1, 1, 1
 	}
 	rvs := make([]*timeseries, 0, len(m))
 	for _, xss := range m {