卡夫卡主题中用于PySpark结构化流的Cassandra Sink [英] Cassandra Sink for PySpark Structured Streaming from Kafka topic

问题描述

我想使用PySpark结构化流API将结构流数据写入Cassandra.

I want to write Structure Streaming Data into Cassandra using PySpark Structured Streaming API.

我的数据流如下:

REST API-> Kafka-> Spark结构化流媒体(PySpark)-> Cassandra

REST API -> Kafka -> Spark Structured Streaming (PySpark) -> Cassandra

下面的源和版本:Spark版本:2.4.3DataStax DSE:6.7.6-1

Source and Version in below: Spark version: 2.4.3 DataStax DSE: 6.7.6-1

初始化火花:

spark = SparkSession.builder\
.master("local[*]")\
.appName("Analytics")\
.config("kafka.bootstrap.servers", "localhost:9092")\
.config("spark.cassandra.connection.host","localhost:9042")\
.getOrCreate()

从Kafka订阅主题:

subscribe topic from Kafka:

df = spark.readStream.format("kafka")\
    .option("kafka.bootstrap.servers", "localhost:9092")\
    .option("subscribe", "topic") \
    .load()

写成Cassandra:

Write into Cassandra:

    w_df_3 = df...

    write_db = w_df_3.writeStream \
    .option("checkpointLocation", '/tmp/check_point/') \
    .format("org.apache.spark.sql.cassandra") \
    .option("keyspace", "analytics") \
    .option("table", "table") \
    .outputMode(outputMode="update")\
    .start()

使用以下命令执行:

$spark-submit --packages org.apache.spark:spark-sql-kafka-0-10_2.11:2.4.0,datastax:spark-cassandra-connector:2.4.0-s_2.11 Analytics.py localhost:9092 topic

在写流到Cassandra时，我面临以下问题/异常:

I am facing below issue/exception while writestream into Cassandra:

py4j.protocol.Py4JJavaError: An error occurred while calling o81.start.
: java.lang.UnsupportedOperationException: Data source org.apache.spark.sql.cassandra does not support streamed writing
    at org.apache.spark.sql.execution.datasources.DataSource.createSink(DataSource.scala:297)
    at org.apache.spark.sql.streaming.DataStreamWriter.start(DataStreamWriter.scala:322)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:244)
    at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:357)
    at py4j.Gateway.invoke(Gateway.java:282)
    at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
    at py4j.commands.CallCommand.execute(CallCommand.java:79)
    at py4j.GatewayConnection.run(GatewayConnection.java:238)
    at java.lang.Thread.run(Thread.java:748)

有人可以帮助我解决和进一步解决吗?任何帮助将不胜感激.

Could anyone help me out on how to resolve and proceed further? Any help will be appreciated.

谢谢.

推荐答案

我在评论中提到，如果您使用的是DSE，则可以将OSS Apache Spark与所谓的

As i mentioned in the comment, if you're using DSE, you can use OSS Apache Spark with so-called BYOS (bring your own spark) - special jar that contains the DataStax's version of Spark Cassandra Connector (SCC) that contains direct support for structured streaming.

由于开源版本还提供了对结构化流的SCC 2.5.0支持，因此您可以简单地将 writeStream 与Cassandra的格式一起使用.2.5.0还包含许多以前在开源中不可用的好东西，例如其他优化等.还有一个

Since SCC 2.5.0 support for structured streaming is also available in open source version, so you can simply use writeStream with format for Cassandra. 2.5.0 also contains a lot of good things previously not available in the open source, such as additional optimizations, etc. There is a blog post that describes them in great details.

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