Cast directly from new PromQL FPoint and HPoint to mimirpb equivalents

[zenador]

What this PR does

Allow casting directly from promql.FPoints to mimirpb.Samples, promql.HPoints to mimirpb.FloatHistogramPairs and histogram.Spans to/from mimirpb.BucketSpans to optimise performance. However, this requires using a pointer in FloatHistogramPair where there wasn't one before, so not sure if we want to keep that part.

Renaming is not done yet. That should probably be done separately, if at all. Not sure if it will be confusing since we've been using Sample for so long, and it will affect much of the codebase, so we need agreement from more people, and maybe also discuss what else we should be renaming for consistency.

Benchmark results here

Which issue(s) this PR fixes or relates to

Fixes #3738 and #4742

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX] (not needed for optimisation)

olegs comment

[krajorama]

I would suggest to add this small addition to the unit tests so we don't have to rely on the integration tests for catching the loop variable problem:

diff --git a/pkg/frontend/querymiddleware/codec_protobuf_test.go b/pkg/frontend/querymiddleware/codec_protobuf_test.go
index 48ebc7cb9..33647e3d1 100644
--- a/pkg/frontend/querymiddleware/codec_protobuf_test.go
+++ b/pkg/frontend/querymiddleware/codec_protobuf_test.go
@@ -45,6 +45,24 @@ var protobufResponseHistogram = mimirpb.FloatHistogram{
 	PositiveBuckets: []float64{100, 200, 300},
 	NegativeBuckets: []float64{400, 500, 600, 700},
 }
+var protobufResponseHistogram2 = mimirpb.FloatHistogram{
+	CounterResetHint: histogram.GaugeType,
+	Schema:           3,
+	ZeroThreshold:    1.23,
+	ZeroCount:        556,
+	Count:            9101,
+	Sum:              789.1,
+	PositiveSpans: []mimirpb.BucketSpan{
+		{Offset: 4, Length: 1},
+		{Offset: 3, Length: 2},
+	},
+	NegativeSpans: []mimirpb.BucketSpan{
+		{Offset: 7, Length: 3},
+		{Offset: 9, Length: 1},
+	},
+	PositiveBuckets: []float64{100, 200, 300},
+	NegativeBuckets: []float64{400, 500, 600, 700},
+}
 
 var protobufCodecScenarios = []struct {
 	name                  string
@@ -258,6 +276,11 @@ var protobufCodecScenarios = []struct {
 							TimestampMs: 1234,
 							Histogram:   protobufResponseHistogram,
 						},
+						{
+							Metric:      []string{"baz2", "blah2"},
+							TimestampMs: 1234,
+							Histogram:   protobufResponseHistogram2,
+						},
 					},
 				},
 			},
@@ -275,6 +298,10 @@ var protobufCodecScenarios = []struct {
 						Labels:     []mimirpb.LabelAdapter{{Name: "baz", Value: "blah"}},
 						Histograms: []mimirpb.FloatHistogramPair{{TimestampMs: 1234, Histogram: &protobufResponseHistogram}},
 					},
+					{
+						Labels:     []mimirpb.LabelAdapter{{Name: "baz2", Value: "blah2"}},
+						Histograms: []mimirpb.FloatHistogramPair{{TimestampMs: 1234, Histogram: &protobufResponseHistogram2}},
+					},
 				},
 			},
 			Headers: expectedProtobufResponseHeaders,

[krajorama]

LGTM