Annotations/Alerting: Add Loki historian store stub (#78363)

* Add Loki historian store stub

* Add composite store

* Use composite store if Loki historian enabled

* Split store interface into read/write

* Make composite + historian stores read only

* Use variadic constructor for composite

* Modify Loki store enable logic

* Use dskit.concurrency.ForEachJob for parallelism

pkg/services/annotations/annotationsimpl/annotations.go

@@ -4,6 +4,7 @@ import (
 	"context"
 
 	"github.com/grafana/grafana/pkg/services/annotations/accesscontrol"
+	"github.com/grafana/grafana/pkg/services/annotations/annotationsimpl/loki"
 
 	"github.com/grafana/grafana/pkg/infra/db"
 	"github.com/grafana/grafana/pkg/infra/log"
@@ -17,7 +18,8 @@ type RepositoryImpl struct {
 	db       db.DB
 	authZ    *accesscontrol.AuthService
 	features featuremgmt.FeatureToggles
-	store    store
+	reader   readStore
+	writer   writeStore
 }
 
 func ProvideService(
@@ -27,27 +29,42 @@ func ProvideService(
 	tagService tag.Service,
 ) *RepositoryImpl {
 	l := log.New("annotations")
+	l.Debug("Initializing annotations service")
+
+	xormStore := NewXormStore(cfg, log.New("annotations.sql"), db, tagService)
+	write := xormStore
+
+	var read readStore
+	historianStore := loki.NewLokiHistorianStore(cfg.UnifiedAlerting.StateHistory, features, db, log.New("annotations.loki"))
+	if historianStore != nil {
+		l.Debug("Using composite read store")
+		read = NewCompositeStore(xormStore, historianStore)
+	} else {
+		l.Debug("Using xorm read store")
+		read = write
+	}
 
 	return &RepositoryImpl{
 		db:       db,
 		features: features,
 		authZ:    accesscontrol.NewAuthService(db, features),
-		store:    NewXormStore(cfg, l, db, tagService),
+		reader:   read,
+		writer:   write,
 	}
 }
 
 func (r *RepositoryImpl) Save(ctx context.Context, item *annotations.Item) error {
-	return r.store.Add(ctx, item)
+	return r.writer.Add(ctx, item)
 }
 
 // SaveMany inserts multiple annotations at once.
 // It does not return IDs associated with created annotations. If you need this functionality, use the single-item Save instead.
 func (r *RepositoryImpl) SaveMany(ctx context.Context, items []annotations.Item) error {
-	return r.store.AddMany(ctx, items)
+	return r.writer.AddMany(ctx, items)
 }
 
 func (r *RepositoryImpl) Update(ctx context.Context, item *annotations.Item) error {
-	return r.store.Update(ctx, item)
+	return r.writer.Update(ctx, item)
 }
 
 func (r *RepositoryImpl) Find(ctx context.Context, query *annotations.ItemQuery) ([]*annotations.ItemDTO, error) {
@@ -56,13 +73,13 @@ func (r *RepositoryImpl) Find(ctx context.Context, query *annotations.ItemQuery)
 		return make([]*annotations.ItemDTO, 0), err
 	}
 
-	return r.store.Get(ctx, query, resources)
+	return r.reader.Get(ctx, query, resources)
 }
 
 func (r *RepositoryImpl) Delete(ctx context.Context, params *annotations.DeleteParams) error {
-	return r.store.Delete(ctx, params)
+	return r.writer.Delete(ctx, params)
 }
 
 func (r *RepositoryImpl) FindTags(ctx context.Context, query *annotations.TagsQuery) (annotations.FindTagsResult, error) {
-	return r.store.GetTags(ctx, query)
+	return r.reader.GetTags(ctx, query)
 }