使用 jdbc 死信的持久演员答案

【问题标题】：Persistent actor using jdbc dead letters使用 jdbc 死信的持久演员
【发布时间】：2021-03-02 09:46:20
【问题描述】：

在使用持久性参与者并使用 jdbc 作为日志时。给我的持久演员的所有消息都是死信。但是，我看不到原因，因为我将它们直接发送给持久演员。

持久性演员代码：

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)
  }
}

测试代码（发送给持久化actor的所有消息都是死信）：

  "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")
    }
  }

【问题讨论】：

标签： akka akka-persistence

【解决方案1】：

当没有正确运行的actor实例时会发生死信。无论消息被发送到的actor是否是持久actor，传递消息的过程都是相同的。

所以，我想当你向它发送消息时，你的持久性actor实际上并没有运行。这可能是因为没有正确配置持久性设置。

我使用 In-Memory 持久性运行了您的代码（将 Cmd 和 Evt 更改为 String 类型）并且它有效。

【讨论】：

【解决方案2】：

感谢您的回复！您是否熟悉 jdbc 插件？我配置了日志/快照和与数据库的平滑连接，它似乎符合插件的文档。您是否可以看到任何错误/遗漏的东西？应用程序.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
 }
}

【讨论】：