scala - 如何确保恒定的Avro模式生成并避免 'Too many schema objects created for x'异常？

在生成带有reactive kafka和avro4s的Avro消息时，出现了可重现的错误。一旦达到客户端的identityMapCapacity(CachedSchemaRegistryClient)，序列化将失败并显示

java.lang.IllegalStateException: Too many schema objects created for <myTopic>-value

这是意外的，因为所有消息都应具有相同的架构-它们是相同case类的序列化。

val avroProducerSettings: ProducerSettings[String, GenericRecord] =
  ProducerSettings(system, Serdes.String().serializer(),
  avroSerde.serializer())
 .withBootstrapServers(settings.bootstrapServer)

val avroProdFlow: Flow[ProducerMessage.Message[String, GenericRecord, String],
                    ProducerMessage.Result[String, GenericRecord, String],
                    NotUsed] = Producer.flow(avroProducerSettings)

val avroQueue: SourceQueueWithComplete[Message[String, GenericRecord, String]] =
  Source.queue(bufferSize, overflowStrategy)
  .via(avroProdFlow)
  .map(logResult)
  .to(Sink.ignore)
  .run()

...
queue.offer(msg)

序列化器是一个KafkaAvroSerializer，用new CachedSchemaRegistryClient(settings.schemaRegistry, 1000)实例化

生成GenericRecord:

def toAvro[A](a: A)(implicit recordFormat: RecordFormat[A]): GenericRecord =
  recordFormat.to(a)

val makeEdgeMessage: (Edge, String) => Message[String, GenericRecord, String] = { (edge, topic) =>
  val edgeAvro: GenericRecord = toAvro(edge)
  val record   = new ProducerRecord[String, GenericRecord](topic, edge.id, edgeAvro)
  ProducerMessage.Message(record, edge.id)
}

该模式是在代码(io.confluent.kafka.serializers.AbstractKafkaAvroSerDe#getSchema，由io.confluent.kafka.serializers.AbstractKafkaAvroSerializer#serializeImpl调用)的深处创建的，对此我没有任何影响，因此我不知道如何解决泄漏。在我看来，这两个融合的项目不能很好地协同工作。

我发现here，here和here的问题似乎无法解决我的用例。

对我来说，目前有两种解决方法:

不使用架构注册表-显然不是一个长期解决方案

创建不依赖于对象标识的自定义SchemaRegistryClient-可行，但我想避免产生比重新实现

更大的问题

有没有一种方法可以根据消息/记录类型生成或缓存一致的架构，并在我的设置中使用它？

最佳答案

编辑2017.11.20

在我的情况下，问题是，携带我的消息的GenericRecord的每个实例都已由包含RecordFormat的不同实例的Schema的不同实例进行了序列化。这里的隐式解析每次都会生成一个新实例。
def toAvro[A](a: A)(implicit recordFormat: RecordFormat[A]): GenericRecord = recordFormat.to(a)
解决方案是将RecordFormat实例固定到val并显式重用。非常感谢https://github.com/heliocentrist的explaining the details。

原始回复:

等待了一会儿(对于github issue也没有答案)之后，我不得不实现自己的SchemaRegistryClient。超过90％的内容是从原始CachedSchemaRegistryClient复制而来的，只是被翻译成scala。使用scala mutable.Map修复了内存泄漏。我尚未进行任何全面的测试，因此使用时需您自担风险。

import java.util

import io.confluent.kafka.schemaregistry.client.rest.entities.{ Config, SchemaString }
import io.confluent.kafka.schemaregistry.client.rest.entities.requests.ConfigUpdateRequest
import io.confluent.kafka.schemaregistry.client.rest.{ RestService, entities }
import io.confluent.kafka.schemaregistry.client.{ SchemaMetadata, SchemaRegistryClient }
import org.apache.avro.Schema

import scala.collection.mutable

class CachingSchemaRegistryClient(val restService: RestService, val identityMapCapacity: Int)
    extends SchemaRegistryClient {

  val schemaCache: mutable.Map[String, mutable.Map[Schema, Integer]] = mutable.Map()
  val idCache: mutable.Map[String, mutable.Map[Integer, Schema]] =
    mutable.Map(null.asInstanceOf[String] -> mutable.Map())
  val versionCache: mutable.Map[String, mutable.Map[Schema, Integer]] = mutable.Map()

  def this(baseUrl: String, identityMapCapacity: Int) {
    this(new RestService(baseUrl), identityMapCapacity)
  }

  def this(baseUrls: util.List[String], identityMapCapacity: Int) {
    this(new RestService(baseUrls), identityMapCapacity)
  }

  def registerAndGetId(subject: String, schema: Schema): Int =
    restService.registerSchema(schema.toString, subject)

  def getSchemaByIdFromRegistry(id: Int): Schema = {
    val restSchema: SchemaString = restService.getId(id)
    (new Schema.Parser).parse(restSchema.getSchemaString)
  }

  def getVersionFromRegistry(subject: String, schema: Schema): Int = {
    val response: entities.Schema = restService.lookUpSubjectVersion(schema.toString, subject)
    response.getVersion.intValue
  }

  override def getVersion(subject: String, schema: Schema): Int = synchronized {
    val schemaVersionMap: mutable.Map[Schema, Integer] =
      versionCache.getOrElseUpdate(subject, mutable.Map())

    val version: Integer = schemaVersionMap.getOrElse(
      schema, {
        if (schemaVersionMap.size >= identityMapCapacity) {
          throw new IllegalStateException(s"Too many schema objects created for $subject!")
        }

        val version = new Integer(getVersionFromRegistry(subject, schema))
        schemaVersionMap.put(schema, version)
        version
      }
    )
    version.intValue()
  }

  override def getAllSubjects: util.List[String] = restService.getAllSubjects()

  override def getByID(id: Int): Schema = synchronized { getBySubjectAndID(null, id) }

  override def getBySubjectAndID(subject: String, id: Int): Schema = synchronized {
    val idSchemaMap: mutable.Map[Integer, Schema] = idCache.getOrElseUpdate(subject, mutable.Map())
    idSchemaMap.getOrElseUpdate(id, getSchemaByIdFromRegistry(id))
  }

  override def getSchemaMetadata(subject: String, version: Int): SchemaMetadata = {
    val response = restService.getVersion(subject, version)
    val id       = response.getId.intValue
    val schema   = response.getSchema
    new SchemaMetadata(id, version, schema)
  }

  override def getLatestSchemaMetadata(subject: String): SchemaMetadata = synchronized {
    val response = restService.getLatestVersion(subject)
    val id       = response.getId.intValue
    val version  = response.getVersion.intValue
    val schema   = response.getSchema
    new SchemaMetadata(id, version, schema)
  }

  override def updateCompatibility(subject: String, compatibility: String): String = {
    val response: ConfigUpdateRequest = restService.updateCompatibility(compatibility, subject)
    response.getCompatibilityLevel
  }

  override def getCompatibility(subject: String): String = {
    val response: Config = restService.getConfig(subject)
    response.getCompatibilityLevel
  }

  override def testCompatibility(subject: String, schema: Schema): Boolean =
    restService.testCompatibility(schema.toString(), subject, "latest")

  override def register(subject: String, schema: Schema): Int = synchronized {
    val schemaIdMap: mutable.Map[Schema, Integer] =
      schemaCache.getOrElseUpdate(subject, mutable.Map())

    val id = schemaIdMap.getOrElse(
      schema, {
        if (schemaIdMap.size >= identityMapCapacity)
          throw new IllegalStateException(s"Too many schema objects created for $subject!")
        val id: Integer = new Integer(registerAndGetId(subject, schema))
        schemaIdMap.put(schema, id)
        idCache(null).put(id, schema)
        id
      }
    )
    id.intValue()
  }
}