From 000c154641d1ce29a856fa6d8885477a1e59131e Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Sun, 4 Aug 2019 19:32:18 +0300
Subject: [PATCH] app/vmselect/promql: tune automatic window adjustement

Increase the windows adjustement for small scrape intervals,
since they usually have higher jitter.

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/139
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/134
---
 app/vmselect/promql/rollup.go      | 23 ++++++++++++++++++++---
 app/vmselect/promql/rollup_test.go | 10 +++++-----
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/app/vmselect/promql/rollup.go b/app/vmselect/promql/rollup.go
index 6099b58c8..a627c209e 100644
--- a/app/vmselect/promql/rollup.go
+++ b/app/vmselect/promql/rollup.go
@@ -231,10 +231,27 @@ func getMaxPrevInterval(timestamps []int64) int64 {
 	}
 	d := (timestamps[len(timestamps)-1] - timestamps[0]) / int64(len(timestamps)-1)
 	if d <= 0 {
-		return 1
+		return int64(maxSilenceInterval)
 	}
-	// Slightly increase d in order to handle possible jitter in scrape interval.
-	return d + (d / 4)
+	// Increase d more for smaller scrape intervals in order to hide possible gaps
+	// when high jitter is present.
+	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/139 .
+	if d <= 2*1000 {
+		return d + 4*d
+	}
+	if d <= 4*1000 {
+		return d + 2*d
+	}
+	if d <= 8*1000 {
+		return d + d
+	}
+	if d <= 16*1000 {
+		return d + d/2
+	}
+	if d <= 32*1000 {
+		return d + d/4
+	}
+	return d + d/8
 }
 
 func removeCounterResets(values []float64) {
diff --git a/app/vmselect/promql/rollup_test.go b/app/vmselect/promql/rollup_test.go
index fdb79c8d3..fcf598b63 100644
--- a/app/vmselect/promql/rollup_test.go
+++ b/app/vmselect/promql/rollup_test.go
@@ -347,7 +347,7 @@ func TestRollupNoWindowNoPoints(t *testing.T) {
 		}
 		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
 		values := rc.Do(nil, testValues, testTimestamps)
-		valuesExpected := []float64{2, 0, 0, 0, 0, 0, 0, nan}
+		valuesExpected := []float64{2, 0, 0, 0, 0, 0, 0, 0}
 		timestampsExpected := []int64{120, 124, 128, 132, 136, 140, 144, 148}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})
@@ -371,15 +371,15 @@ func TestRollupWindowNoPoints(t *testing.T) {
 	t.Run("afterEnd", func(t *testing.T) {
 		rc := rollupConfig{
 			Func:   rollupFirst,
-			Start:  141,
-			End:    171,
+			Start:  161,
+			End:    191,
 			Step:   10,
 			Window: 3,
 		}
 		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
 		values := rc.Do(nil, testValues, testTimestamps)
-		valuesExpected := []float64{34, nan, nan, nan}
-		timestampsExpected := []int64{141, 151, 161, 171}
+		valuesExpected := []float64{34, 34, 34, nan}
+		timestampsExpected := []int64{161, 171, 181, 191}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})
 }