From 0cb66a8f9505f11858f90da5a0dda3aabc552d6a Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Fri, 16 Aug 2019 11:55:10 +0300
Subject: [PATCH] app/vmselect/promql: fix corner-case calculation for `ideriv`

---
 app/vmselect/promql/rollup.go      | 4 ++--
 app/vmselect/promql/rollup_test.go | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/app/vmselect/promql/rollup.go b/app/vmselect/promql/rollup.go
index 16df4755c5..f2272097f6 100644
--- a/app/vmselect/promql/rollup.go
+++ b/app/vmselect/promql/rollup.go
@@ -698,7 +698,7 @@ func rollupIderiv(rfa *rollupFuncArg) float64 {
 			// It is impossible to calculate derivative on 0 or 1 values.
 			return nan
 		}
-		return (values[0] - rfa.prevValue) / float64(timestamps[0]-rfa.prevTimestamp)
+		return (values[0] - rfa.prevValue) / (float64(timestamps[0]-rfa.prevTimestamp) * 1e-3)
 	}
 	vEnd := values[len(values)-1]
 	tEnd := timestamps[len(timestamps)-1]
@@ -722,7 +722,7 @@ func rollupIderiv(rfa *rollupFuncArg) float64 {
 	}
 	dv := vEnd - vStart
 	dt := tEnd - tStart
-	return dv / (float64(dt) / 1000)
+	return dv / (float64(dt) * 1e-3)
 }
 
 func rollupChanges(rfa *rollupFuncArg) float64 {
diff --git a/app/vmselect/promql/rollup_test.go b/app/vmselect/promql/rollup_test.go
index 337d634587..00fbbff374 100644
--- a/app/vmselect/promql/rollup_test.go
+++ b/app/vmselect/promql/rollup_test.go
@@ -56,7 +56,7 @@ func TestRollupIderivDuplicateTimestamps(t *testing.T) {
 		timestamps:    []int64{100},
 	}
 	n = rollupIderiv(rfa)
-	if n != 0.5 {
+	if n != 500 {
 		t.Fatalf("unexpected value; got %v; want %v", n, 0.5)
 	}