HyukjinKwon commented on issue #24946: [SPARK-27234][SS][PYTHON] Use InheritableThreadLocal for current epoch in EpochTracker (to support Python UDFs) URL: https://github.com/apache/spark/pull/24946#issuecomment-505227175 It works after this PR as below: ```python from pyspark.sql.functions import col, pandas_udf, PandasUDFType @pandas_udf("int", PandasUDFType.SCALAR_ITER) def the_udf(iterator): for col1_batch in iterator: yield col1_batch spark \ .readStream \ .format("rate") \ .load() \ .withColumn("foo", the_udf(col("value"))) \ .writeStream \ .format("console") \ .trigger(continuous="5 second").start() ``` Before: ``` ... Caused by: java.util.NoSuchElementException: None.get at scala.None$.get(Option.scala:366) at scala.None$.get(Option.scala:364) at org.apache.spark.sql.execution.streaming.continuous.ContinuousQueuedDataReader.next(ContinuousQueuedDataReader.scala:116) at org.apache.spark.sql.execution.streaming.continuous.ContinuousDataSourceRDD$$anon$1.getNext(ContinuousDataSourceRDD.scala:93) at org.apache.spark.sql.execution.streaming.continuous.ContinuousDataSourceRDD$$anon$1.getNext(ContinuousDataSourceRDD.scala:91) at org.apache.spark.util.NextIterator.hasNext(NextIterator.scala:73) at org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage1.processNext(Unknown Source) at org.apache.spark.sql.execution.BufferedRowIterator.hasNext(BufferedRowIterator.java:43) at org.apache.spark.sql.execution.WholeStageCodegenExec$$anon$1.hasNext(WholeStageCodegenExec.scala:701) at scala.collection.Iterator$$anon$10.hasNext(Iterator.scala:458) ... ``` After: ``` ... ------------------------------------------- Batch: 3 ------------------------------------------- +--------------------+-----+---+ | timestamp|value|foo| +--------------------+-----+---+ |2019-06-25 09:05:...| 9| 9| |2019-06-25 09:05:...| 2| 2| |2019-06-25 09:05:...| 10| 10| |2019-06-25 09:05:...| 11| 11| |2019-06-25 09:05:...| 5| 5| |2019-06-25 09:05:...| 3| 3| |2019-06-25 09:05:...| 1| 1| |2019-06-25 09:05:...| 6| 6| |2019-06-25 09:05:...| 4| 4| |2019-06-25 09:05:...| 8| 8| |2019-06-25 09:05:...| 7| 7| |2019-06-25 09:05:...| 0| 0| +--------------------+-----+---+ ... ``` Because each epoch couldn't be referred in writer thread (to Python process). Each UDF will be executed each execution per each epoch.
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