我一直在尝试从Scala 2.11的Spark结构化流(2.4.4)中读取Kafka的avro序列化消息。为此,我使用了spark-avro(下面的依赖项)。我使用confluent-kafka库从python生成kafka消息。Spark流能够使用模式使用消息,但是不能正确读取字段的值。我准备了一个简单的示例来显示问题,代码在这里可用:https://github.com/anigmo97/SimpleExamples/tree/master/Spark_streaming_kafka_avro_scala
我用python创建记录,记录的模式是:
{
"type": "record",
"namespace": "example",
"name": "RawRecord",
"fields": [
{"name": "int_field","type": "int"},
{"name": "string_field","type": "string"}
]
}
它们是这样生成的:
from time import sleep
from confluent_kafka.avro import AvroProducer, load, loads
def generate_records():
avro_producer_settings = {
'bootstrap.servers': "localhost:19092",
'group.id': 'groupid',
'schema.registry.url': "http://127.0.0.1:8081"
}
producer = AvroProducer(avro_producer_settings)
key_schema = loads('"string"')
value_schema = load("schema.avsc")
i = 1
while True:
row = {"int_field": int(i), "string_field": str(i)}
producer.produce(topic="avro_topic", key="key-{}".format(i),
value=row, key_schema=key_schema, value_schema=value_schema)
print(row)
sleep(1)
i+=1
Spark结构化流传输的消耗(在Scala中是这样完成的:
import org.apache.spark.sql.{ Dataset, Row}
import org.apache.spark.sql.streaming.{ OutputMode, StreamingQuery}
import org.apache.spark.sql.avro._
...
try {
log.info("----- reading schema")
val jsonFormatSchema = new String(Files.readAllBytes(
Paths.get("./src/main/resources/schema.avsc")))
val ds:Dataset[Row] = sparkSession
.readStream
.format("kafka")
.option("kafka.bootstrap.servers", kafkaServers)
.option("subscribe", topic)
.load()
val output:Dataset[Row] = ds
.select(from_avro(ds.col("value"), jsonFormatSchema) as "record")
.select("record.*")
output.printSchema()
var query: StreamingQuery = output.writeStream.format("console")
.option("truncate", "false").outputMode(OutputMode.Append()).start();
query.awaitTermination();
} catch {
case e: Exception => log.error("onApplicationEvent error: ", e)
//case _: Throwable => log.error("onApplicationEvent error:")
}
...
在spark中打印架构,虽然avro架构不允许这样做,但字段可为空是很奇怪的。Spark显示了这一点:
root
|-- int_field: integer (nullable = true)
|-- string_field: string (nullable = true)
我已经用python的另一个使用者检查了消息,消息很好,但是独立于消息内容,火花显示了这一点。
+---------+------------+
|int_field|string_field|
+---------+------------+
|0 | |
+---------+------------+
使用的主要依赖项是:
<properties>
<spark.version>2.4.4</spark.version>
<scala.version>2.11</scala.version>
</properties>
<dependency>
<groupId>org.apache.spark</groupId>
<artifactId>spark-core_${scala.version}</artifactId>
<version>${spark.version}</version>
</dependency>
<dependency>
<groupId>org.apache.spark</groupId>
<artifactId>spark-sql_${scala.version}</artifactId>
<version>${spark.version}</version>
</dependency>
<dependency>
<groupId>org.apache.spark</groupId>
<artifactId>spark-avro_${scala.version}</artifactId>
<version>${spark.version}</version>
</dependency>
<dependency>
<groupId>org.apache.spark</groupId>
<artifactId>spark-streaming_${scala.version}</artifactId>
<version>${spark.version}</version>
</dependency>
<dependency>
<groupId>org.apache.spark</groupId>
<artifactId>spark-sql-kafka-0-10_${scala.version}</artifactId>
<version>${spark.version}</version>
</dependency>
有人知道为什么会这样吗?
谢谢。重现该错误的代码在这里:
https://github.com/anigmo97/SimpleExamples/tree/master/Spark_streaming_kafka_avro_scala
问题是我在python中使用confluent_kafka库我正在火花结构化流中读取avro消息使用spark-avro库。
Confluent_kafka库使用confluent的avro格式并触发avro使用标准avro格式读取。
区别在于,为了使用架构注册表,融合了avro在消息中添加四个字节,以指示哪个架构应该使用。
为了能够使用融合的avro并从spark结构中读取它流式传输,我为Abris替换了spark-avro库(abris允许将Avro和融合的Avro与Spark集成在一起)。https://github.com/AbsaOSS/ABRiS
问题是我在python中使用confluent_kafka库我正在火花结构化流中读取avro消息使用spark-avro库。
Confluent_kafka库使用confluent的avro格式并触发avro使用标准avro格式读取。
区别在于,为了使用架构注册表,融合了avro在消息中添加四个字节,以指示哪个架构应该使用。
为了能够使用融合的avro并从spark结构中读取它流式传输,我为Abris替换了spark-avro库(abris允许将Avro和融合的Avro与Spark集成在一起)。https://github.com/AbsaOSS/ABRiS
我的依赖项如下更改:
<properties>
<spark.version>2.4.4</spark.version>
<scala.version>2.11</scala.version>
</properties>
<!-- SPARK- AVRO -->
<dependency>
<groupId>org.apache.spark</groupId>
<artifactId>spark-avro_${scala.version}</artifactId>
<version>${spark.version}</version>
</dependency>
<!-- SPARK -AVRO AND CONFLUENT-AVRO -->
<dependency>
<groupId>za.co.absa</groupId>
<artifactId>abris_2.11</artifactId>
<version>3.1.1</version>
</dependency>
并且在这里您可以看到一个简单的示例,该示例获取整个数据集并将其序列化为avro和合流avro。
var input: Dataset[Row] = sparkSession.readStream
//.format("org.apache.spark.sql.kafka010.KafkaSourceProvider")
.format("kafka")
.option("kafka.bootstrap.servers", kafkaServers)
.option("subscribe", topicConsumer)
.option("failOnDataLoss", "false")
// .option("startingOffsets", "latest")
// .option("startingOffsets", "earliest")
.load();
// READ WITH spark-avro library (standard avro)
val jsonFormatSchema = new String(Files.readAllBytes(Paths.get("./src/main/resources/schema.avsc")))
var inputConfluentAvroDeserialized: Dataset[Row] = input
.select(from_avro(functions.col("value"), jsonFormatSchema) as "record")
.select("record.*")
//READ WITH Abris library (confuent avro)
val schemaRegistryConfig = Map(
SchemaManager.PARAM_SCHEMA_REGISTRY_URL -> "http://localhost:8081",
SchemaManager.PARAM_SCHEMA_REGISTRY_TOPIC -> topicConsumer,
SchemaManager.PARAM_VALUE_SCHEMA_NAMING_STRATEGY -> SchemaManager.SchemaStorageNamingStrategies.TOPIC_NAME, // choose a subject name strategy
SchemaManager.PARAM_VALUE_SCHEMA_ID -> "latest" // set to "latest" if you want the latest schema version to used
)
var inputConfluentAvroDeserialized: Dataset[Row] = inputConfluentAvroSerialized
.select(from_confluent_avro(functions.col("value"), schemaRegistryConfig) as "record")
.select("record.*")