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[英]How to convert Spark Streaming data into Spark DataFrame
[英]Convert Spark Structure Streaming DataFrames to Pandas DataFrame
我有一个设置为从Kafka主题使用的Spark Streaming App,我需要使用一些Pandas Dataframe中的API,但是当我尝试将其转换时,我得到了
: org.apache.spark.sql.AnalysisException: Queries with streaming sources must be executed with writeStream.start();;
kafka
at org.apache.spark.sql.catalyst.analysis.UnsupportedOperationChecker$.org$apache$spark$sql$catalyst$analysis$UnsupportedOperationChecker$$throwError(UnsupportedOperationChecker.scala:297)
at org.apache.spark.sql.catalyst.analysis.UnsupportedOperationChecker$$anonfun$checkForBatch$1.apply(UnsupportedOperationChecker.scala:36)
at org.apache.spark.sql.catalyst.analysis.UnsupportedOperationChecker$$anonfun$checkForBatch$1.apply(UnsupportedOperationChecker.scala:34)
at org.apache.spark.sql.catalyst.trees.TreeNode.foreachUp(TreeNode.scala:127)
at org.apache.spark.sql.catalyst.analysis.UnsupportedOperationChecker$.checkForBatch(UnsupportedOperationChecker.scala:34)
at org.apache.spark.sql.execution.QueryExecution.assertSupported(QueryExecution.scala:63)
at org.apache.spark.sql.execution.QueryExecution.withCachedData$lzycompute(QueryExecution.scala:74)
at org.apache.spark.sql.execution.QueryExecution.withCachedData(QueryExecution.scala:72)
at org.apache.spark.sql.execution.QueryExecution.optimizedPlan$lzycompute(QueryExecution.scala:78)
at org.apache.spark.sql.execution.QueryExecution.optimizedPlan(QueryExecution.scala:78)
at org.apache.spark.sql.execution.QueryExecution.completeString(QueryExecution.scala:219)
at org.apache.spark.sql.execution.QueryExecution.toString(QueryExecution.scala:202)
at org.apache.spark.sql.execution.SQLExecution$.withNewExecutionId(SQLExecution.scala:62)
at org.apache.spark.sql.Dataset.withNewExecutionId(Dataset.scala:2832)
at org.apache.spark.sql.Dataset.collectToPython(Dataset.scala:2809)
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:745)
这是我的python代码
spark = SparkSession\
.builder\
.appName("sparkDf to pandasDf")\
.getOrCreate()
sparkDf = spark.readStream\
.format("kafka")\
.option("kafka.bootstrap.servers", "kafkahost:9092")\
.option("subscribe", "mytopic")\
.option("startingOffsets", "earliest")\
.load()
pandas_df = sparkDf.toPandas()
query = sparkDf.writeStream\
.outputMode("append")\
.format("console")\
.option("truncate", "false")\
.trigger(processingTime="5 seconds")\
.start()\
.awaitTermination()
现在我知道我正在创建流数据帧的另一个实例,但是无论我在哪里尝试使用start()和awaitTermination(),我都会遇到相同的错误。
有任何想法吗?
TL; DR这样的操作就是行不通的。
现在我知道我正在创建流数据帧的另一个实例
好吧,问题是您真的没有。 toPandas
调用的DataFrame
在驱动程序节点的内存中创建了一个简单的本地非分布式Pandas DataFrame
。
它不仅与Spark不相关,而且由于抽象与结构化流本质上不兼容DataFrame
表示一组固定的元组,而结构化流则表示无限的元组流。
目前尚不清楚您要实现的目标,这可能是XY问题,但是如果您确实需要将Pandas与结构化流一起使用,则可以尝试使用pandas_udf
- SCALAR
和GROUPED_MAP
变体至少兼容基本的基于时间的触发器(也可能支持其他变体,尽管某些组合显然没有任何意义,并且我不知道任何正式的兼容性列表)。
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