Important fix using indices in events by tag.

build.sbt

@@ -12,7 +12,7 @@ publishLocal := {}
 lazy val commonSettings = Seq(
   name := "akka-reactivemongo-plugin",
   organization := "null-vector",
-  version := s"1.5.1",
+  version := s"1.5.2",
   scalaVersion := scala213,
   crossScalaVersions := supportedScalaVersions,
   scalacOptions := Seq(

core/src/main/scala/org/nullvector/Collections.scala

@@ -55,8 +55,15 @@ class Collections(system: ExtendedActorSystem) extends Actor with ActorLogging {
       verifiedNames.clear()
       promisedDone success Done
 
-    case GetJournals(response) =>
-      val collections = database.flatMap(_.collectionNames.map(_.filter(_.startsWith(journalPrefix))).flatMap { names =>
+    case GetJournals(response, collectionNames) =>
+      val collections = database.flatMap(_
+        .collectionNames.map { allNames =>
+        val journalNames = allNames.filter(_.startsWith(journalPrefix))
+        collectionNames match {
+          case Nil => journalNames
+          case _ =>  journalNames.filter(name => collectionNames.exists(colName => name.endsWith(colName)))
+        }
+      }.flatMap { names =>
         Future.traverse(names) { name =>
           val promisedCollection = Promise[BSONCollection]
           promisedCollection completeWith verifiedJournalCollection(name)
@@ -67,7 +74,7 @@ class Collections(system: ExtendedActorSystem) extends Actor with ActorLogging {
 
     case CheckHealth(ack) =>
       val collections = Promise[List[BSONCollection]]
-      context.self ! GetJournals(collections)
+      context.self ! GetJournals(collections, Nil)
       val eventualDone = collections.future.map(_.headOption).flatMap {
         case Some(collection) => collection.find(BSONDocument.empty).one.map(_ => Done)
         case None => Future.successful(Done)
@@ -162,10 +169,16 @@ class Collections(system: ExtendedActorSystem) extends Actor with ActorLogging {
   }
 
   private def ensureTagIndex(indexesManager: CollectionIndexesManager): Future[Unit] = {
-    ensureIndex(index(Seq(
+    val tagsById = ensureIndex(index(Seq(
       "_id" -> IndexType.Ascending,
       Fields.tags -> IndexType.Ascending,
-    ), Some("_tags"), unique = true, sparse = true), indexesManager)
+    ), Some("tags_by_id"), unique = true, sparse = true), indexesManager)
+
+    val allTags = ensureIndex(index(Seq(
+      Fields.tags -> IndexType.Ascending,
+    ), Some("tags"), sparse = true), indexesManager)
+
+    tagsById flatMap (_ => allTags)
   }
 
   private def ensureIndex(index: Aux[BSONSerializationPack.type], indexesManager: CollectionIndexesManager): Future[Unit] = {
@@ -209,7 +222,7 @@ object Collections {
 
   case class GetSnapshotCollectionNameFor(persistentId: String, response: Promise[BSONCollection]) extends Command
 
-  case class GetJournals(response: Promise[List[BSONCollection]]) extends Command
+  case class GetJournals(response: Promise[List[BSONCollection]], collectionNames: List[String]) extends Command
 
   case class SetDatabaseProvider(databaseProvider: DatabaseProvider, ack: Promise[Done]) extends Command
 

core/src/main/scala/org/nullvector/ReactiveMongoDriver.scala

@@ -58,9 +58,10 @@ class ReactiveMongoDriver(system: ExtendedActorSystem) extends Extension {
     promise.future
   }
 
-  def journals(): Future[List[BSONCollection]] = {
+
+  def journals(collectionNames: List[String] = Nil): Future[List[BSONCollection]] = {
     val promise = Promise[List[BSONCollection]]()
-    collections ! GetJournals(promise)
+    collections ! GetJournals(promise, collectionNames)
     promise.future
   }
 

core/src/main/scala/org/nullvector/query/EventsQueries.scala

@@ -108,7 +108,7 @@ trait EventsQueries
   }
 
   def eventsByTagQuery(tags: Seq[String], offset: Offset): Source[EventEnvelope, NotUsed] = {
-    Source.future(rxDriver.journals())
+    Source.future(rxDriver.journals(collectionNames))
       .withAttributes(ActorAttributes.dispatcher(ReactiveMongoPlugin.pluginDispatcherName))
       .mapConcat(identity)
       .splitWhen(_ => true)
@@ -127,12 +127,17 @@ trait EventsQueries
 
     import collection.AggregationFramework._
 
+    val filterByOffsetExp = filterByOffset(offset)
     val stages: List[PipelineOperator] = List(
-      Match(query(Fields.tags) ++ filterByOffset(offset)),
+      Match(query(Fields.tags) ++ filterByOffsetExp),
       UnwindField(Fields.events),
       Match(query(s"${Fields.events}.${Fields.tags}")),
     )
-    val hint = Some(collection.hint(BSONDocument("_id" -> 1, Fields.tags -> 1)))
+    val hint = filterByOffsetExp match {
+      case BSONDocument.empty => Some(collection.hint(BSONDocument(Fields.tags -> 1)))
+      case _ => Some(collection.hint(BSONDocument("_id" -> 1, Fields.tags -> 1)))
+    }
+
     rxDriver.explainAgg(collection)(QueryType.EventsByTag, stages, hint)
 
     def aggregate(implicit producer: CursorProducer[BSONDocument]): producer.ProducedCursor = {

core/src/main/scala/org/nullvector/query/ReactiveMongoJournalProvider.scala

@@ -16,10 +16,17 @@ class ReactiveMongoJournalProvider(system: ExtendedActorSystem) extends ReadJour
 
   import akka.actor.typed.scaladsl.adapter._
 
-  override val scaladslReadJournal: ReactiveMongoScalaReadJournal = UnderlyingPersistenceFactory(
-    new ReactiveMongoScalaReadJournalImpl(system),
-    new FromMemoryReadJournal(system.toTyped)
-  )(system)
+  override val scaladslReadJournal: ReactiveMongoScalaReadJournal = createUnderlyingFactory(Nil)
+
+  def readJournalFor(collectionNames: List[String]) = createUnderlyingFactory(collectionNames)
+
+  private def createUnderlyingFactory(names: List[String]) = {
+    UnderlyingPersistenceFactory(
+      new ReactiveMongoScalaReadJournalImpl(system, names),
+      new FromMemoryReadJournal(system.toTyped)
+    )(system)
+  }
+
 
   override val javadslReadJournal: ReactiveMongoJavaReadJournal = new ReactiveMongoJavaReadJournal(scaladslReadJournal)
 }

core/src/main/scala/org/nullvector/query/ReactiveMongoScalaReadJournalImpl.scala

@@ -12,7 +12,7 @@ import java.util.concurrent.TimeUnit
 import scala.concurrent.ExecutionContext
 import scala.concurrent.duration._
 
-class ReactiveMongoScalaReadJournalImpl(system: ExtendedActorSystem)
+class ReactiveMongoScalaReadJournalImpl(system: ExtendedActorSystem, protected val collectionNames: List[String])
   extends akka.persistence.query.scaladsl.ReadJournal
     with EventsQueries
     with PersistenceIdsQueries with ReactiveMongoScalaReadJournal {

core/src/test/scala/org/nullvector/queries/ReactiveMongoReadJournalSpec.scala

@@ -37,7 +37,7 @@ class ReactiveMongoReadJournalSpec() extends FlatSpec with TestKitBase with Impl
   val reactiveMongoJournalImpl: ReactiveMongoJournalImpl = new ReactiveMongoJournalImpl(ConfigFactory.load(), system)
 
   implicit val materializer: Materializer = Materializer.matFromSystem(system)
-  val readJournal: ReactiveMongoScalaReadJournal = ReactiveMongoJournalProvider(system).scaladslReadJournal
+  val readJournal: ReactiveMongoScalaReadJournal = ReactiveMongoJournalProvider(system).readJournalFor(Nil)
   private val serializer = ReactiveMongoEventSerializer(system.toTyped)
   serializer.addAdapter(new SomeEventAdapter())