Persistent actor using jdbc dead letters - akka

Question

While using persistent actors and using jdbc for the journal. All messages to my persistent actor are dead letters. However, I cannot see the reason for this since I send them directly to the persistent actor.
Persistent actor code:
case class ExampleState(events: List[String] = Nil) {
def updated(evt: Evt): ExampleState = copy(evt.data :: events)
def size: Int = events.length
override def toString: String = events.reverse.toString
}
class ExampleActor extends PersistentActor {
override def persistenceId = "sample-id-1"
var state = ExampleState()
def updateState(event: Evt): Unit = {
state = state.updated(event)
}
def numEvents =
state.size
override def receiveRecover: Receive = {
case evt: Evt => updateState(evt)
case SnapshotOffer(_, snapshot: ExampleState) => state = snapshot
}
val snapShotInterval = 1000
override def receiveCommand: Receive= {
case Cmd(data) => {
println("in the command code block")
persist(Evt(s"${data}-${numEvents}")) { event => {
updateState(event)
context.system.eventStream.publish(event)
if (lastSequenceNr % snapShotInterval == 0 && lastSequenceNr != 0)
saveSnapshot(state)
}
}
}
case Shutdown => context.stop(self)
case "print"=>println(state)
}
}
Test code (all messages sent to persistent actor are the dead letters):
"The example persistent actor" should {
"Test Command" in {
val persistentActor = system.actorOf(Props[ExampleActor](),"examplePersistentactor")
Thread.sleep(2000)
println("before the send")
persistentActor ! Cmd("foo")
persistentActor ! Cmd("bar")
persistentActor ! Cmd("fizz")
persistentActor ! Cmd("buzz")
persistentActor ! "print"
Thread.sleep(10000)
persistentActor ! Shutdown
println("after messages should be sent and received")
}
}

Answer 1

Dead letters happens when there is no actor instance properly running. The delivery message process is the same no matter whether the actor to which message was sent is a persistent actor or not.
So, I suppose your persistent actor is not actually running when you send a message to it. That could be because of persistence settings are not configured properly.
I ran your code (changing Cmd and Evt for String type) using In-Memory persistence and it worked.

Answer 2

Thanks for your reply! Are you by any chance familiar with the jdbc plugin? I configured the journal/snapshot and slick connection to the database and it seems to fit with the documentation of the plugin. Is there anything you can see that is wrong/missing by any chance?
application.conf:
akka {
loglevel = DEBUG
}
# Copyright 2016 Dennis Vriend
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# general.conf is included only for shared settings used for the akka-persistence-jdbc tests
include "general.conf"
akka {
persistence {
journal {
plugin = "jdbc-journal"
# Enable the line below to automatically start the journal when the actorsystem is started
auto-start-journals = ["jdbc-journal"]
}
snapshot-store {
plugin = "jdbc-snapshot-store"
# Enable the line below to automatically start the snapshot-store when the actorsystem is started
auto-start-snapshot-stores = ["jdbc-snapshot-store"]
}
}
}
jdbc-journal {
slick = ${slick}
}
# the akka-persistence-snapshot-store in use
jdbc-snapshot-store {
slick = ${slick}
}
# the akka-persistence-query provider in use
jdbc-read-journal {
slick = ${slick}
}
slick {
profile = "slick.jdbc.MySQLProfile$"
db {
url = "jdbc:mysql://localhost:3306/squirrel_persistence/mysql?cachePrepStmts=true&cacheCallableStmts=true&cacheServerConfiguration=true&useLocalSessionState=true&elideSetAutoCommits=true&alwaysSendSetIsolation=false&enableQueryTimeouts=false&connectionAttributes=none&verifyServerCertificate=false&useSSL=false&allowPublicKeyRetrieval=true&useUnicode=true&useLegacyDatetimeCode=false&serverTimezone=UTC&rewriteBatchedStatements=true"
user = "root"
password = ""
driver = "com.mysql.jdbc.Driver"
numThreads = 5
maxConnections = 5
minConnections = 1
}
}