prom rw v2 exporter order samples by timestamp (open-telemetry#39980)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
As prometheus prefers to ingest timeseries in order by timestamp we are
sorting them.

<!-- Issue number (e.g. open-telemetry#1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Fixes open-telemetry#33661 partially

<!--Describe what testing was performed and which tests were added.-->
#### Testing
Added unit test

I think it's okay to skip changelog here, given it's not changing the
API and not really user facing given RW2 is not yet ready to be used.

Co-authored-by: Alex Boten <[email protected]>

Author: 2 people

exporter/prometheusremotewriteexporter/exporter_v2.go

@@ -102,13 +102,11 @@ func (prwe *prwExporter) handleExportV2(ctx context.Context, symbolsTable writev
 	}
 
 	requests = append(requests, &writev2.Request{
-		// TODO sort
 		// Prometheus requires time series to be sorted by Timestamp to avoid out of order problems.
 		// See:
 		// * https://github.com/open-telemetry/wg-prometheus/issues/10
 		// * https://github.com/open-telemetry/opentelemetry-collector/issues/2315
-		// Timeseries: orderBySampleTimestamp(tsArray),
-		Timeseries: tsArray,
+		Timeseries: orderBySampleTimestampV2(tsArray),
 		Symbols:    symbolsTable.Symbols(),
 	})
 

exporter/prometheusremotewriteexporter/helper.go

@@ -9,6 +9,7 @@ import (
 	"sort"
 
 	"github.com/prometheus/prometheus/prompb"
+	writev2 "github.com/prometheus/prometheus/prompb/io/prometheus/write/v2"
 )
 
 type batchTimeSeriesState struct {
@@ -120,3 +121,13 @@ func orderBySampleTimestamp(tsArray []prompb.TimeSeries) []prompb.TimeSeries {
 	}
 	return tsArray
 }
+
+func orderBySampleTimestampV2(tsArray []writev2.TimeSeries) []writev2.TimeSeries {
+	for i := range tsArray {
+		sL := tsArray[i].Samples
+		sort.Slice(sL, func(i, j int) bool {
+			return sL[i].Timestamp < sL[j].Timestamp
+		})
+	}
+	return tsArray
+}

exporter/prometheusremotewriteexporter/helper_test.go

@@ -8,6 +8,7 @@ import (
 	"testing"
 
 	"github.com/prometheus/prometheus/prompb"
+	writev2 "github.com/prometheus/prometheus/prompb/io/prometheus/write/v2"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -248,3 +249,112 @@ func TestEnsureTimeseriesPointsAreSortedByTimestamp(t *testing.T) {
 		}
 	}
 }
+
+// Ensure that before a prompb.WriteRequest is created, that the points per TimeSeries
+// are sorted by Timestamp value, to prevent Prometheus from barfing when it gets poorly
+// sorted values. See issues:
+// * https://github.com/open-telemetry/wg-prometheus/issues/10
+// * https://github.com/open-telemetry/opentelemetry-collector/issues/2315
+func TestEnsureTimeseriesPointsAreSortedByTimestampV2(t *testing.T) {
+	outOfOrder := []writev2.TimeSeries{
+		{
+			Samples: []writev2.Sample{
+				{
+					Value:     10.11,
+					Timestamp: 1000,
+				},
+				{
+					Value:     7.81,
+					Timestamp: 2,
+				},
+				{
+					Value:     987.81,
+					Timestamp: 1,
+				},
+				{
+					Value:     18.22,
+					Timestamp: 999,
+				},
+			},
+		},
+		{
+			Samples: []writev2.Sample{
+				{
+					Value:     99.91,
+					Timestamp: 5,
+				},
+				{
+					Value:     4.33,
+					Timestamp: 3,
+				},
+				{
+					Value:     47.81,
+					Timestamp: 4,
+				},
+				{
+					Value:     18.22,
+					Timestamp: 8,
+				},
+			},
+		},
+	}
+	got := orderBySampleTimestampV2(outOfOrder)
+
+	// We must ensure that the resulting Timeseries' sample points are sorted by Timestamp.
+	want := []writev2.TimeSeries{
+		{
+			Samples: []writev2.Sample{
+				{
+					Value:     987.81,
+					Timestamp: 1,
+				},
+				{
+					Value:     7.81,
+					Timestamp: 2,
+				},
+				{
+					Value:     18.22,
+					Timestamp: 999,
+				},
+				{
+					Value:     10.11,
+					Timestamp: 1000,
+				},
+			},
+		},
+		{
+			Samples: []writev2.Sample{
+				{
+					Value:     4.33,
+					Timestamp: 3,
+				},
+				{
+					Value:     47.81,
+					Timestamp: 4,
+				},
+				{
+					Value:     99.91,
+					Timestamp: 5,
+				},
+				{
+					Value:     18.22,
+					Timestamp: 8,
+				},
+			},
+		},
+	}
+	assert.Equal(t, want, got)
+
+	// For a full sanity/logical check, assert that EVERY
+	// Sample has a Timestamp bigger than its prior values.
+	for ti, ts := range got {
+		for i := range ts.Samples {
+			si := ts.Samples[i]
+			for j := 0; j < i; j++ {
+				sj := ts.Samples[j]
+				assert.LessOrEqual(t, sj.Timestamp, si.Timestamp, "Timeseries[%d]: Sample[%d].Timestamp(%d) > Sample[%d].Timestamp(%d)",
+					ti, j, sj.Timestamp, i, si.Timestamp)
+			}
+		}
+	}
+}