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Align yrate/yincrease/ydelta with Prometheus 3.x (start, end] semantics#20

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Align yrate/yincrease/ydelta with Prometheus 3.x (start, end] semantics #20

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000cb3d
Align yrate/yincrease/ydelta with Prometheus 3.x range semantics
ColinDKelley Apr 19, 2026
8e94af7
Refresh yrate showcase expectations for (start, end] semantics
ColinDKelley Apr 19, 2026
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13 changes: 8 additions & 5 deletions promql/functions.go
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Original file line numberDiff line numberDiff line change
Expand Up@@ -338,7 +338,10 @@ func extendedRate(vals []parser.Value, args parser.Expressions, enh *EvalNodeHel
// yIncrease is a utility function for yincrease/yrate/ydelta.
// It calculates the increase of the range (allowing for counter resets if isCounter is true),
// taking into account the sample at the end of the previous range (just before rangeStartMsec).
// It returns the result across the range [rangeStartMsec, rangeEndMsec).
// It returns the result across the range (rangeStartMsec, rangeEndMsec]. The left-open,
// right-closed convention matches the Prometheus 3.x range-selector semantics
// (see prometheus/prometheus#13213) so that a sample whose timestamp lands exactly on
// a range boundary is attributed to the later range, never to both or neither.
// It always extends the preceding sample's value until the next sample, including the
// unwritten origin sample value at the start of every time series.
//
Expand All@@ -357,8 +360,8 @@ func yIncrease(points []FPoint, rangeStartMsec, rangeEndMsec int64, isCounter bo
// The points are in time order, so we can just walk the list once and remember the last values
// seen "before" and "in" range. If there are no values in range, we use the last value before range
// so that the increase is 0.
for i := 0; i < len(points) && points[i].T < rangeEndMsec; i++ { // Only consider points in [rangeStartMsec, rangeEndMsec).
if points[i].T >= rangeStartMsec {
for i := 0; i < len(points) && points[i].T <= rangeEndMsec; i++ { // Only consider points in (rangeStartMsec, rangeEndMsec].
if points[i].T > rangeStartMsec {
if isCounter && points[i].F < lastInRange { // Counter reset (process restart).
inRangeRestartSkew += lastInRange
}
Expand All@@ -373,8 +376,8 @@ func yIncrease(points []FPoint, rangeStartMsec, rangeEndMsec int64, isCounter bo

// rangeFromSelectors extracts points, rangeStartMsec, rangeEndMsec, and rangeSeconds
// from the common (Matrix, MatrixSelector) arguments supplied to yincrease/yrate/ydelta.
// The range is [rangeStartMsec, rangeEndMsec). That is, every sample in range has the property:
// rangeStartMsec <= sample.T < rangeEndMsec.
// The range is (rangeStartMsec, rangeEndMsec]. That is, every sample in range has the property:
// rangeStartMsec < sample.T <= rangeEndMsec.
func rangeFromSelectors(vals []parser.Value, args parser.Expressions, enh *EvalNodeHelper) ([]FPoint, int64, int64, float64) {
ms := args[0].(*parser.MatrixSelector)
vs := ms.VectorSelector.(*parser.VectorSelector)
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6 changes: 3 additions & 3 deletions promql/promqltest/testdata/functions.test
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Expand Up@@ -25,7 +25,7 @@ eval instant at 25s xrate(http_requests[50s])

eval instant at 25s yrate(http_requests[50s])
{path="/foo"} 0.04
{path="/bar"} 0.42
{path="/bar"} 0.52

# 2. Eval 1 second earlier compared to (1).
# * path="/foo" rate should be same or fractionally higher ("shorter" sample, same actual increase);
Expand DownExpand Up@@ -74,8 +74,8 @@ eval instant at 75s xrate(http_requests[50s])
{path="/bar"} 0.8

eval instant at 75s yrate(http_requests[50s])
{path="/foo"} 0.06
{path="/bar"} 1.32
{path="/foo"} 0.02
{path="/bar"} 0.8

# 5. Eval 1s earlier compared to (4).
# * path="/foo" rate should be same or fractionally lower ("longer" sample, same actual increase).
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