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promql: add temporary debug logging to yrate start-timestamp codepath #35

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dasbus wants to merge 2 commits into from
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promql: add temporary debug logging to yrate start-timestamp codepath #35

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b895acc
promql: add temporary debug logging to yrate start-timestamp codepath
dasbus Aug 13, 2026
0b865be
promql: add TODO tag to yrate ST debug logging for tracked revert
dasbus Sep 2, 2026
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26 changes: 25 additions & 1 deletion promql/yrate_funcs.go
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Original file line number Diff line number Diff line change
Expand Up @@ -14,10 +14,17 @@
package promql

import (
"log/slog"

"github.com/prometheus/prometheus/promql/parser"
"github.com/prometheus/prometheus/util/annotations"
)

// TODO(sprice): TEMPORARY debug logger for start-timestamp verification.
// Revert this logger and its call sites once ST integration testing on
// red.prodref.us-east-1 has validated yrate/yincrease start-timestamp handling.
var yrateSTLogger = slog.Default().With("component", "yrate-st-debug")

// 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).
Expand Down Expand Up @@ -66,6 +73,17 @@ func yIncrease(points []FPoint, rangeStartMsec, rangeEndMsec int64, isCounter bo
if isCounter && isYCounterReset(startTimestamps, prevST, currentST, points[i].T, rangeStartMsec, points[i].F, lastInRange) {
// Counter reset: accumulate as if 0 had come before this sample.
inRangeResetIncreases += lastInRange
// TEMPORARY: log counter reset detection details.
stTriggered := startTimestamps != nil && currentST != 0 && currentST != prevST
yrateSTLogger.Info("yrate counter reset detected",
"value_drop", points[i].F < lastInRange,
"st_triggered", stTriggered,
"prev_st", prevST,
"current_st", currentST,
"sample_t", points[i].T,
"sample_value", points[i].F,
"last_in_range", lastInRange,
)

if !foundInRangeSample {
// This reset was *also* the first in-range sample. Since we just counted
Expand Down Expand Up @@ -132,8 +150,14 @@ func funcYrate(_ []Vector, matrixVals Matrix, args parser.Expressions, enh *Eval
func yStartTimestamps(points []FPoint, enh *EvalNodeHelper) []int64 {
if enh.StartTimestamps != nil && len(enh.StartTimestamps.Floats) == len(points) {
startTimestamps := enh.StartTimestamps.Floats
for _, startTimestamp := range startTimestamps {
for i, startTimestamp := range startTimestamps {
if startTimestamp != 0 {
// TEMPORARY: log when start timestamps are found for yrate/yincrease evaluation.
yrateSTLogger.Info("start timestamps found for yrate evaluation",
"num_points", len(points),
"first_nonzero_st_index", i,
"first_nonzero_st_value", startTimestamp,
)
return startTimestamps
}
}
Expand Down
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