fix: (Bug) correct resultType when storing instant query results in cache

cmd/loki/loki-local-with-memcached.yaml

@@ -16,6 +16,10 @@ common:
     kvstore:
       store: inmemory
 
+limits_config:
+  split_instant_metric_queries_by_interval: '10m'
+
+
 query_range:
   align_queries_with_step: true
   cache_index_stats_results: true

pkg/querier/queryrange/codec.go

@@ -22,6 +22,7 @@ import (
 	json "github.com/json-iterator/go"
 	"github.com/opentracing/opentracing-go"
 	otlog "github.com/opentracing/opentracing-go/log"
+	"github.com/prometheus/common/model"
 	"github.com/prometheus/prometheus/model/timestamp"
 
 	"github.com/grafana/loki/pkg/loghttp"
@@ -1271,15 +1272,22 @@ func (Codec) MergeResponse(responses ...queryrangebase.Response) (queryrangebase
 		return nil, errors.New("merging responses requires at least one response")
 	}
 	var mergedStats stats.Result
-	switch responses[0].(type) {
+	switch res := responses[0].(type) {
+	// LokiPromResponse type is used for both instant and range queries.
+	// Meaning, values that are merged can be either vector or matrix types.
 	case *LokiPromResponse:
 
+		codec := queryrangebase.PrometheusCodecForRangeQueries
+		if res.Response.Data.ResultType == model.ValVector.String() {
+			codec = queryrangebase.PrometheusCodecForInstantQueries
+		}
+
 		promResponses := make([]queryrangebase.Response, 0, len(responses))
 		for _, res := range responses {
 			mergedStats.MergeSplit(res.(*LokiPromResponse).Statistics)
 			promResponses = append(promResponses, res.(*LokiPromResponse).Response)
 		}
-		promRes, err := queryrangebase.PrometheusCodec.MergeResponse(promResponses...)
+		promRes, err := codec.MergeResponse(promResponses...)
 		if err != nil {
 			return nil, err
 		}
@@ -1800,7 +1808,7 @@ func NewEmptyResponse(r queryrangebase.Request) (queryrangebase.Response, error)
 		}
 		if _, ok := expr.(syntax.SampleExpr); ok {
 			return &LokiPromResponse{
-				Response: queryrangebase.NewEmptyPrometheusResponse(),
+				Response: queryrangebase.NewEmptyPrometheusResponse(model.ValMatrix), // range metric query
 			}, nil
 		}
 		return &LokiResponse{

pkg/querier/queryrange/instant_metric_cache.go

@@ -49,8 +49,6 @@ func (cfg *InstantMetricCacheConfig) Validate() error {
 	return cfg.ResultsCacheConfig.Validate()
 }
 
-type instantMetricExtractor struct{}
-
 func NewInstantMetricCacheMiddleware(
 	log log.Logger,
 	limits Limits,

pkg/querier/queryrange/limits_test.go

@@ -240,7 +240,7 @@ func Test_MaxQueryParallelism(t *testing.T) {
 		defer count.Dec()
 		// simulate some work
 		time.Sleep(20 * time.Millisecond)
-		return base.NewEmptyPrometheusResponse(), nil
+		return base.NewEmptyPrometheusResponse(model.ValMatrix), nil
 	})
 	ctx := user.InjectOrgID(context.Background(), "foo")
 
@@ -271,7 +271,7 @@ func Test_MaxQueryParallelismLateScheduling(t *testing.T) {
 	h := base.HandlerFunc(func(_ context.Context, _ base.Request) (base.Response, error) {
 		// simulate some work
 		time.Sleep(20 * time.Millisecond)
-		return base.NewEmptyPrometheusResponse(), nil
+		return base.NewEmptyPrometheusResponse(model.ValMatrix), nil
 	})
 	ctx := user.InjectOrgID(context.Background(), "foo")
 
@@ -298,7 +298,7 @@ func Test_MaxQueryParallelismDisable(t *testing.T) {
 	h := base.HandlerFunc(func(_ context.Context, _ base.Request) (base.Response, error) {
 		// simulate some work
 		time.Sleep(20 * time.Millisecond)
-		return base.NewEmptyPrometheusResponse(), nil
+		return base.NewEmptyPrometheusResponse(model.ValMatrix), nil
 	})
 	ctx := user.InjectOrgID(context.Background(), "foo")
 

pkg/querier/queryrange/queryrangebase/marshaling_test.go

@@ -29,7 +29,7 @@ func BenchmarkPrometheusCodec_DecodeResponse(b *testing.B) {
 	b.ReportAllocs()
 
 	for n := 0; n < b.N; n++ {
-		_, err := PrometheusCodec.DecodeResponse(context.Background(), &http.Response{
+		_, err := PrometheusCodecForRangeQueries.DecodeResponse(context.Background(), &http.Response{
 			StatusCode:    200,
 			Body:          io.NopCloser(bytes.NewReader(encodedRes)),
 			ContentLength: int64(len(encodedRes)),
@@ -51,7 +51,7 @@ func BenchmarkPrometheusCodec_EncodeResponse(b *testing.B) {
 	b.ReportAllocs()
 
 	for n := 0; n < b.N; n++ {
-		_, err := PrometheusCodec.EncodeResponse(context.Background(), nil, res)
+		_, err := PrometheusCodecForRangeQueries.EncodeResponse(context.Background(), nil, res)
 		require.NoError(b, err)
 	}
 }

pkg/querier/queryrange/queryrangebase/query_range.go

@@ -38,14 +38,26 @@ var (
 	errNegativeStep   = httpgrpc.Errorf(http.StatusBadRequest, "zero or negative query resolution step widths are not accepted. Try a positive integer")
 	errStepTooSmall   = httpgrpc.Errorf(http.StatusBadRequest, "exceeded maximum resolution of 11,000 points per time series. Try increasing the value of the step parameter")
 
-	// PrometheusCodec is a codec to encode and decode Prometheus query range requests and responses.
-	PrometheusCodec = &prometheusCodec{}
+	// PrometheusCodecForRangeQueries is a codec to encode and decode Loki range metric query requests and responses.
+	PrometheusCodecForRangeQueries = &prometheusCodec{
+		resultType: model.ValMatrix,
+	}
+
+	// PrometheusCodecForInstantQueries is a codec to encode and decode Loki range metric query requests and responses.
+	PrometheusCodecForInstantQueries = &prometheusCodec{
+		resultType: model.ValVector,
+	}
 
 	// Name of the cache control header.
 	cacheControlHeader = "Cache-Control"
 )
 
-type prometheusCodec struct{}
+type prometheusCodec struct {
+	// prometheusCodec is used to merge multiple response of either range (matrix) or instant queries(vector).
+	// when creating empty responses during merge, it need to be aware what kind of valueType it should create with.
+	// helps other middlewares to filter the correct result type.
+	resultType model.ValueType
+}
 
 // WithStartEnd clones the current `PrometheusRequest` with a new `start` and `end` timestamp.
 func (q *PrometheusRequest) WithStartEnd(start, end time.Time) Request {
@@ -125,19 +137,19 @@ func (resp *PrometheusResponse) SetHeader(name, value string) {
 }
 
 // NewEmptyPrometheusResponse returns an empty successful Prometheus query range response.
-func NewEmptyPrometheusResponse() *PrometheusResponse {
+func NewEmptyPrometheusResponse(v model.ValueType) *PrometheusResponse {
 	return &PrometheusResponse{
 		Status: StatusSuccess,
 		Data: PrometheusData{
-			ResultType: model.ValMatrix.String(),
+			ResultType: v.String(),
 			Result:     []SampleStream{},
 		},
 	}
 }
 
-func (prometheusCodec) MergeResponse(responses ...Response) (Response, error) {
+func (p prometheusCodec) MergeResponse(responses ...Response) (Response, error) {
 	if len(responses) == 0 {
-		return NewEmptyPrometheusResponse(), nil
+		return NewEmptyPrometheusResponse(p.resultType), nil
 	}
 
 	promResponses := make([]*PrometheusResponse, 0, len(responses))
@@ -155,7 +167,7 @@ func (prometheusCodec) MergeResponse(responses ...Response) (Response, error) {
 	response := PrometheusResponse{
 		Status: StatusSuccess,
 		Data: PrometheusData{
-			ResultType: model.ValMatrix.String(),
+			ResultType: p.resultType.String(),
 			Result:     matrixMerge(promResponses),
 		},
 	}

pkg/querier/queryrange/queryrangebase/query_range_test.go

@@ -33,7 +33,7 @@ func TestResponse(t *testing.T) {
 				Header:     http.Header{"Content-Type": []string{"application/json"}},
 				Body:       io.NopCloser(bytes.NewBuffer([]byte(tc.body))),
 			}
-			resp, err := PrometheusCodec.DecodeResponse(context.Background(), response, nil)
+			resp, err := PrometheusCodecForRangeQueries.DecodeResponse(context.Background(), response, nil)
 			require.NoError(t, err)
 			assert.Equal(t, tc.expected, resp)
 
@@ -44,7 +44,7 @@ func TestResponse(t *testing.T) {
 				Body:          io.NopCloser(bytes.NewBuffer([]byte(tc.body))),
 				ContentLength: int64(len(tc.body)),
 			}
-			resp2, err := PrometheusCodec.EncodeResponse(context.Background(), nil, resp)
+			resp2, err := PrometheusCodecForRangeQueries.EncodeResponse(context.Background(), nil, resp)
 			require.NoError(t, err)
 			assert.Equal(t, response, resp2)
 		})
@@ -262,7 +262,7 @@ func TestMergeAPIResponses(t *testing.T) {
 			},
 		}} {
 		t.Run(tc.name, func(t *testing.T) {
-			output, err := PrometheusCodec.MergeResponse(tc.input...)
+			output, err := PrometheusCodecForRangeQueries.MergeResponse(tc.input...)
 			require.NoError(t, err)
 			require.Equal(t, tc.expected, output)
 		})

pkg/querier/queryrange/queryrangebase/results_cache_test.go

@@ -414,7 +414,7 @@ func TestResultsCache(t *testing.T) {
 		c,
 		resultscache.ConstSplitter(day),
 		mockLimits{},
-		PrometheusCodec,
+		PrometheusCodecForRangeQueries,
 		PrometheusResponseExtractor{},
 		nil,
 		nil,
@@ -461,7 +461,7 @@ func TestResultsCacheRecent(t *testing.T) {
 		c,
 		resultscache.ConstSplitter(day),
 		mockLimits{maxCacheFreshness: 10 * time.Minute},
-		PrometheusCodec,
+		PrometheusCodecForRangeQueries,
 		PrometheusResponseExtractor{},
 		nil,
 		nil,
@@ -572,7 +572,7 @@ func TestResultsCacheShouldCacheFunc(t *testing.T) {
 				c,
 				resultscache.ConstSplitter(day),
 				mockLimits{maxCacheFreshness: 10 * time.Minute},
-				PrometheusCodec,
+				PrometheusCodecForRangeQueries,
 				PrometheusResponseExtractor{},
 				nil,
 				tc.shouldCache,