From e74fb23189229de3c8ee98f415a36b1c4c9516ca Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Sun, 18 Aug 2019 21:07:59 +0300
Subject: [PATCH] app/vmselect/promql: add `scrape_interval(q[d])` function,
 which would return scrape interval for `q` over `d`

---
 app/vmselect/promql/rollup.go      | 18 ++++++++++++++++++
 app/vmselect/promql/rollup_test.go | 28 ++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/app/vmselect/promql/rollup.go b/app/vmselect/promql/rollup.go
index d8ff249d0..c1d82237e 100644
--- a/app/vmselect/promql/rollup.go
+++ b/app/vmselect/promql/rollup.go
@@ -46,6 +46,7 @@ var rollupFuncs = map[string]newRollupFunc{
 	"integrate":          newRollupFuncOneArg(rollupIntegrate),
 	"ideriv":             newRollupFuncOneArg(rollupIderiv),
 	"lifetime":           newRollupFuncOneArg(rollupLifetime),
+	"scrape_interval":    newRollupFuncOneArg(rollupScrapeInterval),
 	"rollup":             newRollupFuncOneArg(rollupFake),
 	"rollup_rate":        newRollupFuncOneArg(rollupFake), // + rollupFuncsRemoveCounterResets
 	"rollup_deriv":       newRollupFuncOneArg(rollupFake),
@@ -62,6 +63,8 @@ var rollupFuncsMayAdjustWindow = map[string]bool{
 	"deriv_fast":      true,
 	"irate":           true,
 	"rate":            true,
+	"lifetime":        true,
+	"scrape_interval": true,
 }
 
 var rollupFuncsRemoveCounterResets = map[string]bool{
@@ -741,6 +744,21 @@ func rollupLifetime(rfa *rollupFuncArg) float64 {
 	return float64(timestamps[len(timestamps)-1]-rfa.prevTimestamp) * 1e-3
 }
 
+func rollupScrapeInterval(rfa *rollupFuncArg) float64 {
+	// Calculate the average interval between data points.
+	timestamps := rfa.timestamps
+	if math.IsNaN(rfa.prevValue) {
+		if len(timestamps) < 2 {
+			return nan
+		}
+		return float64(timestamps[len(timestamps)-1]-timestamps[0]) * 1e-3 / float64(len(timestamps)-1)
+	}
+	if len(timestamps) == 0 {
+		return nan
+	}
+	return (float64(timestamps[len(timestamps)-1]-rfa.prevTimestamp) * 1e-3) / float64(len(timestamps))
+}
+
 func rollupChanges(rfa *rollupFuncArg) float64 {
 	// There is no need in handling NaNs here, since they must be cleaned up
 	// before calling rollup funcs.
diff --git a/app/vmselect/promql/rollup_test.go b/app/vmselect/promql/rollup_test.go
index 2ce43cc24..f13dc617b 100644
--- a/app/vmselect/promql/rollup_test.go
+++ b/app/vmselect/promql/rollup_test.go
@@ -612,6 +612,34 @@ func TestRollupFuncsNoWindow(t *testing.T) {
 		timestampsExpected := []int64{0, 40, 80, 120, 160}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})
+	t.Run("scrape_interval", func(t *testing.T) {
+		rc := rollupConfig{
+			Func:   rollupScrapeInterval,
+			Start:  0,
+			End:    160,
+			Step:   40,
+			Window: 0,
+		}
+		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
+		values := rc.Do(nil, testValues, testTimestamps)
+		valuesExpected := []float64{nan, 0.010333333333333333, 0.011, 0.013333333333333334, 0.01}
+		timestampsExpected := []int64{0, 40, 80, 120, 160}
+		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
+	})
+	t.Run("scrape_interval", func(t *testing.T) {
+		rc := rollupConfig{
+			Func:   rollupScrapeInterval,
+			Start:  0,
+			End:    160,
+			Step:   40,
+			Window: 80,
+		}
+		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
+		values := rc.Do(nil, testValues, testTimestamps)
+		valuesExpected := []float64{nan, 0.010333333333333333, 0.010714285714285714, 0.012, 0.0125}
+		timestampsExpected := []int64{0, 40, 80, 120, 160}
+		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
+	})
 	t.Run("changes", func(t *testing.T) {
 		rc := rollupConfig{
 			Func:   rollupChanges,