Merge pull request #19273 from talp-traiana/per-19221-eager-plugin-initialization

=per #19221 Eager initialization of persistence plugins

akka-docs/rst/java/lambda-persistence.rst

@@ -787,6 +787,11 @@ Plugin development requires the following imports:
 
 .. includecode:: code/docs/persistence/LambdaPersistencePluginDocTest.java#plugin-imports
 
+By default, persistence plugins are started on-demand, as they are used. In some case, however, it might be beneficial
+to start a certain plugin eagerly. In order to do that, you should first add the ``akka.persistence.Persistence``
+under the ``akka.extensions`` key. Then, specify the IDs of plugins you wish to start automatically under
+``akka.persistence.journal.auto-start-journals`` and ``akka.persistence.snapshot-store.auto-start-snapshot-stores``.
+
 Journal plugin API
 ------------------
 

akka-docs/rst/java/persistence.rst

@@ -738,6 +738,11 @@ Plugin development requires the following imports:
 
 .. includecode:: code/docs/persistence/PersistencePluginDocTest.java#plugin-imports
 
+By default, persistence plugins are started on-demand, as they are used. In some case, however, it might be beneficial
+to start a certain plugin eagerly. In order to do that, you should first add the ``akka.persistence.Persistence``
+under the ``akka.extensions`` key. Then, specify the IDs of plugins you wish to start automatically under
+``akka.persistence.journal.auto-start-journals`` and ``akka.persistence.snapshot-store.auto-start-snapshot-stores``.
+
 .. _journal-plugin-api-java:
 
 Journal plugin API

akka-docs/rst/scala/persistence.rst

@@ -797,6 +797,11 @@ Plugin development requires the following imports:
 
 .. includecode:: code/docs/persistence/PersistencePluginDocSpec.scala#plugin-imports
 
+By default, persistence plugins are started on-demand, as they are used. In some case, however, it might be beneficial
+to start a certain plugin eagerly. In order to do that, you should first add the ``akka.persistence.Persistence``
+under the ``akka.extensions`` key. Then, specify the IDs of plugins you wish to start automatically under
+``akka.persistence.journal.auto-start-journals`` and ``akka.persistence.snapshot-store.auto-start-snapshot-stores``.
+
 .. _journal-plugin-api:
 
 Journal plugin API

akka-persistence/src/main/resources/reference.conf

@@ -16,6 +16,8 @@ akka.persistence {
         # Persistent actor or view can override `journalPluginId` method 
         # in order to rely on a different journal plugin.
         plugin = ""
+        # List of journal plugins to start automatically. Use "" for the default journal plugin.
+        auto-start-journals = []
     }
     snapshot-store {
         # Absolute path to the snapshot plugin configuration entry used by
@@ -27,6 +29,8 @@ akka.persistence {
         # Note that Cluster Sharding is using snapshots, so if you
         # use Cluster Sharding you need to define a snapshot store plugin. 
         plugin = ""
+        # List of snapshot stores to start automatically. Use "" for the default snapshot store.
+        auto-start-snapshot-stores = []
     }
     # used as default-snapshot store if no plugin configured 
     # (see `akka.persistence.snapshot-store`)

akka-persistence/src/main/scala/akka/persistence/Persistence.scala

@@ -5,15 +5,14 @@
 package akka.persistence
 
 import java.util.concurrent.atomic.AtomicReference
+import java.util.function.Consumer
 import akka.actor._
-import akka.dispatch.Dispatchers
 import akka.event.{ Logging, LoggingAdapter }
-import akka.persistence.journal.{ AsyncWriteJournal, EventAdapters, IdentityEventAdapters, ReplayFilter }
+import akka.persistence.journal.{ EventAdapters, IdentityEventAdapters }
 import akka.util.Helpers.ConfigOps
 import com.typesafe.config.Config
 import scala.annotation.tailrec
 import scala.concurrent.duration._
-import java.util.Locale
 import akka.util.Reflect
 import scala.util.control.NonFatal
 
@@ -168,6 +167,20 @@ class Persistence(val system: ExtendedActorSystem) extends Extension {
   private val journalFallbackConfigPath = "akka.persistence.journal-plugin-fallback"
   private val snapshotStoreFallbackConfigPath = "akka.persistence.snapshot-store-plugin-fallback"
 
+
+  config.getStringList("journal.auto-start-journals").forEach(new Consumer[String] {
+    override def accept(id: String): Unit = {
+      log.info(s"Auto-starting journal plugin `$id`")
+      journalFor(id)
+    }
+  })
+  config.getStringList("snapshot-store.auto-start-snapshot-stores").forEach(new Consumer[String] {
+    override def accept(id: String): Unit = {
+      log.info(s"Auto-starting snapshot store `$id`")
+      snapshotStoreFor(id)
+    }
+  })
+
   /**
    * Returns an [[akka.persistence.journal.EventAdapters]] object which serves as a per-journal collection of bound event adapters.
    * If no adapters are registered for a given journal the EventAdapters object will simply return the identity

akka-persistence/src/test/scala/akka/persistence/journal/leveldb/PersistencePluginProxySpec.scala

@@ -9,7 +9,6 @@ import akka.persistence._
 import akka.persistence.journal.PersistencePluginProxy
 import akka.testkit.{ TestProbe, AkkaSpec }
 import com.typesafe.config.ConfigFactory
-import scala.concurrent.duration._
 
 object PersistencePluginProxySpec {
   lazy val config = ConfigFactory.parseString(
@@ -54,6 +53,8 @@ object PersistencePluginProxySpec {
 
   def targetAddressConfig(system: ActorSystem) = ConfigFactory.parseString(
     s"""
+      |akka.extensions = ["akka.persistence.Persistence"]
+      |akka.persistence.journal.auto-start-journals = [""]
       |akka.persistence.journal.proxy.target-journal-address = "${system.asInstanceOf[ExtendedActorSystem].provider.getDefaultAddress}"
       |akka.persistence.snapshot-store.proxy.target-snapshot-store-address = "${system.asInstanceOf[ExtendedActorSystem].provider.getDefaultAddress}"
     """.stripMargin)