promql: refactor: split out aggregations over range

The new function `rangeEvalAgg` is mostly a copy of `rangeEval`, but
without `initSeries` which we don't need and inlining the callback to
`aggregation()`.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

promql/engine.go

@@ -1291,6 +1291,172 @@ func (ev *evaluator) rangeEval(prepSeries func(labels.Labels, *EvalSeriesHelper)
 	return mat, warnings
 }
 
+func (ev *evaluator) rangeEvalAgg(aggExpr *parser.AggregateExpr, sortedGrouping []string) (Matrix, annotations.Annotations) {
+	numSteps := int((ev.endTimestamp-ev.startTimestamp)/ev.interval) + 1
+	matrixes := make([]Matrix, 2)
+	origMatrixes := make([]Matrix, 2)
+	originalNumSamples := ev.currentSamples
+
+	var warnings annotations.Annotations
+	for i, e := range []parser.Expr{aggExpr.Param, aggExpr.Expr} {
+		// Functions will take string arguments from the expressions, not the values.
+		if e != nil && e.Type() != parser.ValueTypeString {
+			// ev.currentSamples will be updated to the correct value within the ev.eval call.
+			val, ws := ev.eval(e)
+			warnings.Merge(ws)
+			matrixes[i] = val.(Matrix)
+
+			// Keep a copy of the original point slices so that they
+			// can be returned to the pool.
+			origMatrixes[i] = make(Matrix, len(matrixes[i]))
+			copy(origMatrixes[i], matrixes[i])
+		}
+	}
+
+	vectors := make([]Vector, 2)    // Input vectors for the function.
+	args := make([]parser.Value, 2) // Argument to function.
+	biggestLen := len(matrixes[1])
+	enh := &EvalNodeHelper{Out: make(Vector, 0, biggestLen)}
+	type seriesAndTimestamp struct {
+		Series
+		ts int64
+	}
+	seriess := make(map[uint64]seriesAndTimestamp, biggestLen) // Output series by series hash.
+	tempNumSamples := ev.currentSamples
+
+	seriesHelpers := make([][]EvalSeriesHelper, 2)
+	bufHelpers := make([][]EvalSeriesHelper, 2)
+	// Prepare a function to initialise series helpers with the grouping key.
+	buf := make([]byte, 0, 1024)
+
+	seriesHelpers[1] = make([]EvalSeriesHelper, len(matrixes[1]))
+	bufHelpers[1] = make([]EvalSeriesHelper, len(matrixes[1]))
+
+	for si, series := range matrixes[1] {
+		seriesHelpers[1][si].groupingKey, buf = generateGroupingKey(series.Metric, sortedGrouping, aggExpr.Without, buf)
+	}
+
+	for ts := ev.startTimestamp; ts <= ev.endTimestamp; ts += ev.interval {
+		if err := contextDone(ev.ctx, "expression evaluation"); err != nil {
+			ev.error(err)
+		}
+		// Reset number of samples in memory after each timestamp.
+		ev.currentSamples = tempNumSamples
+		// Gather input vectors for this timestamp.
+		for i := range []parser.Expr{aggExpr.Param, aggExpr.Expr} {
+			vectors[i] = vectors[i][:0]
+			bufHelpers[i] = bufHelpers[i][:0]
+
+			for si, series := range matrixes[i] {
+				switch {
+				case len(series.Floats) > 0 && series.Floats[0].T == ts:
+					vectors[i] = append(vectors[i], Sample{Metric: series.Metric, F: series.Floats[0].F, T: ts})
+					// Move input vectors forward so we don't have to re-scan the same
+					// past points at the next step.
+					matrixes[i][si].Floats = series.Floats[1:]
+				case len(series.Histograms) > 0 && series.Histograms[0].T == ts:
+					vectors[i] = append(vectors[i], Sample{Metric: series.Metric, H: series.Histograms[0].H, T: ts})
+					matrixes[i][si].Histograms = series.Histograms[1:]
+				default:
+					continue
+				}
+				if seriesHelpers[i] != nil {
+					bufHelpers[i] = append(bufHelpers[i], seriesHelpers[i][si])
+				}
+				ev.currentSamples++
+				if ev.currentSamples > ev.maxSamples {
+					ev.error(ErrTooManySamples(env))
+				}
+			}
+			args[i] = vectors[i]
+			ev.samplesStats.UpdatePeak(ev.currentSamples)
+		}
+
+		// Make the function call.
+		enh.Ts = ts
+		var param float64
+		if aggExpr.Param != nil {
+			param = args[0].(Vector)[0].F
+		}
+		result, ws := ev.aggregation(aggExpr, sortedGrouping, param, args[1].(Vector), bufHelpers[1], enh)
+
+		enh.Out = result[:0] // Reuse result vector.
+		warnings.Merge(ws)
+
+		vecNumSamples := result.TotalSamples()
+		ev.currentSamples += vecNumSamples
+		// When we reset currentSamples to tempNumSamples during the next iteration of the loop it also
+		// needs to include the samples from the result here, as they're still in memory.
+		tempNumSamples += vecNumSamples
+		ev.samplesStats.UpdatePeak(ev.currentSamples)
+
+		if ev.currentSamples > ev.maxSamples {
+			ev.error(ErrTooManySamples(env))
+		}
+		ev.samplesStats.UpdatePeak(ev.currentSamples)
+
+		// If this could be an instant query, shortcut so as not to change sort order.
+		if ev.endTimestamp == ev.startTimestamp {
+			if result.ContainsSameLabelset() {
+				ev.errorf("vector cannot contain metrics with the same labelset")
+			}
+			mat := make(Matrix, len(result))
+			for i, s := range result {
+				if s.H == nil {
+					mat[i] = Series{Metric: s.Metric, Floats: []FPoint{{T: ts, F: s.F}}}
+				} else {
+					mat[i] = Series{Metric: s.Metric, Histograms: []HPoint{{T: ts, H: s.H}}}
+				}
+			}
+			ev.currentSamples = originalNumSamples + mat.TotalSamples()
+			ev.samplesStats.UpdatePeak(ev.currentSamples)
+			return mat, warnings
+		}
+
+		// Add samples in output vector to output series.
+		for _, sample := range result {
+			h := sample.Metric.Hash()
+			ss, ok := seriess[h]
+			if ok {
+				if ss.ts == ts { // If we've seen this output series before at this timestamp, it's a duplicate.
+					ev.errorf("vector cannot contain metrics with the same labelset")
+				}
+				ss.ts = ts
+			} else {
+				ss = seriesAndTimestamp{Series{Metric: sample.Metric}, ts}
+			}
+			if sample.H == nil {
+				if ss.Floats == nil {
+					ss.Floats = getFPointSlice(numSteps)
+				}
+				ss.Floats = append(ss.Floats, FPoint{T: ts, F: sample.F})
+			} else {
+				if ss.Histograms == nil {
+					ss.Histograms = getHPointSlice(numSteps)
+				}
+				ss.Histograms = append(ss.Histograms, HPoint{T: ts, H: sample.H})
+			}
+			seriess[h] = ss
+		}
+	}
+
+	// Reuse the original point slices.
+	for _, m := range origMatrixes {
+		for _, s := range m {
+			putFPointSlice(s.Floats)
+			putHPointSlice(s.Histograms)
+		}
+	}
+	// Assemble the output matrix. By the time we get here we know we don't have too many samples.
+	mat := make(Matrix, 0, len(seriess))
+	for _, ss := range seriess {
+		mat = append(mat, ss.Series)
+	}
+	ev.currentSamples = originalNumSamples + mat.TotalSamples()
+	ev.samplesStats.UpdatePeak(ev.currentSamples)
+	return mat, warnings
+}
+
 // evalSubquery evaluates given SubqueryExpr and returns an equivalent
 // evaluated MatrixSelector in its place. Note that the Name and LabelMatchers are not set.
 func (ev *evaluator) evalSubquery(subq *parser.SubqueryExpr) (*parser.MatrixSelector, int, annotations.Annotations) {
@@ -1343,12 +1509,6 @@ func (ev *evaluator) eval(expr parser.Expr) (parser.Value, annotations.Annotatio
 		sortedGrouping := e.Grouping
 		slices.Sort(sortedGrouping)
 
-		// Prepare a function to initialise series helpers with the grouping key.
-		buf := make([]byte, 0, 1024)
-		initSeries := func(series labels.Labels, h *EvalSeriesHelper) {
-			h.groupingKey, buf = generateGroupingKey(series, sortedGrouping, e.Without, buf)
-		}
-
 		unwrapParenExpr(&e.Param)
 		param := unwrapStepInvariantExpr(e.Param)
 		unwrapParenExpr(&param)
@@ -1367,13 +1527,7 @@ func (ev *evaluator) eval(expr parser.Expr) (parser.Value, annotations.Annotatio
 			}, e.Expr)
 		}
 
-		return ev.rangeEval(initSeries, func(v []parser.Value, sh [][]EvalSeriesHelper, enh *EvalNodeHelper) (Vector, annotations.Annotations) {
-			var param float64
-			if e.Param != nil {
-				param = v[0].(Vector)[0].F
-			}
-			return ev.aggregation(e, sortedGrouping, param, v[1].(Vector), sh[1], enh)
-		}, e.Param, e.Expr)
+		return ev.rangeEvalAgg(e, sortedGrouping)
 
 	case *parser.Call:
 		call := FunctionCalls[e.Func.Name]