Unistore: Only Shadow Search Traffic when running on modes > 0 (#110302)

* Unistore: Only Shadow Search Traffic when running on modes > 0

Signed-off-by: Maicon Costa <maiconscosta@gmail.com>

---------

Signed-off-by: Maicon Costa <maiconscosta@gmail.com>

pkg/storage/unified/resource/search_client.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/grafana/grafana/pkg/infra/log"
 	"github.com/grafana/grafana/pkg/services/featuremgmt"
+	"github.com/grafana/grafana/pkg/storage/legacysql/dualwrite"
 	"github.com/grafana/grafana/pkg/storage/unified/resourcepb"
 )
 
@@ -38,6 +39,7 @@ var (
 type DualWriter interface {
 	IsEnabled(schema.GroupResource) bool
 	ReadFromUnified(context.Context, schema.GroupResource) (bool, error)
+	Status(ctx context.Context, gr schema.GroupResource) (dualwrite.StorageStatus, error)
 }
 
 func NewSearchClient(dual DualWriter, gr schema.GroupResource, unifiedClient resourcepb.ResourceIndexClient,
@@ -99,6 +101,28 @@ func calculateMatchPercentage(legacyUIDs, unifiedUIDs map[string]struct{}) float
 	return float64(matches) / float64(len(legacyUIDs)) * 100.0
 }
 
+// If dual reader feature flag is enabled, and legacy is the main storage,
+// and we are writing to unified (which means we are effectively dual writing),
+// then make a background call to unified
+func shouldMakeBackgroundCall(ctx context.Context, features featuremgmt.FeatureToggles, dual DualWriter, gr schema.GroupResource) (bool, error) {
+	unifiedIsMainStorage, err := dual.ReadFromUnified(ctx, gr)
+	if err != nil {
+		return false, err
+	}
+
+	status, err := dual.Status(ctx, gr)
+	if err != nil {
+		return false, err
+	}
+
+	res := features != nil &&
+		features.IsEnabledGlobally(featuremgmt.FlagUnifiedStorageSearchDualReaderEnabled) &&
+		!unifiedIsMainStorage &&
+		status.WriteUnified
+
+	return res, nil
+}
+
 func (s *searchWrapper) GetStats(ctx context.Context, in *resourcepb.ResourceStatsRequest,
 	opts ...grpc.CallOption) (*resourcepb.ResourceStatsResponse, error) {
 	client := s.legacyClient
@@ -110,9 +134,12 @@ func (s *searchWrapper) GetStats(ctx context.Context, in *resourcepb.ResourceSta
 		client = s.unifiedClient
 	}
 
-	// If dual reader feature flag is enabled, and legacy is the main storage,
-	// make a background call to unified
-	if s.features != nil && s.features.IsEnabledGlobally(featuremgmt.FlagUnifiedStorageSearchDualReaderEnabled) && !unified {
+	makeBackgroundCall, err := shouldMakeBackgroundCall(ctx, s.features, s.dual, s.groupResource)
+	if err != nil {
+		return nil, err
+	}
+
+	if makeBackgroundCall {
 		// Create background context with timeout but ignore parent cancelation
 		ctxBg := context.WithoutCancel(ctx)
 
@@ -143,9 +170,12 @@ func (s *searchWrapper) Search(ctx context.Context, in *resourcepb.ResourceSearc
 		client = s.unifiedClient
 	}
 
-	// If dual reader feature flag is enabled, and legacy is the main storage,
-	// make a background call to unified and compare results
-	if s.features != nil && s.features.IsEnabledGlobally(featuremgmt.FlagUnifiedStorageSearchDualReaderEnabled) && !unified {
+	makeBackgroundCall, err := shouldMakeBackgroundCall(ctx, s.features, s.dual, s.groupResource)
+	if err != nil {
+		return nil, err
+	}
+
+	if makeBackgroundCall {
 		// Get the legacy result first
 		legacyResponse, legacyErr := s.legacyClient.Search(ctx, in, opts...)
 		if legacyErr != nil {