[jira] [Commented] (SPARK-20065) Empty output files created for aggregation query in append mode

["Wenchen Fan (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-20065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16092488#comment-16092488 ] 

Wenchen Fan commented on SPARK-20065:
-------------------------------------

Does https://github.com/apache/spark/pull/18654 fix this issue?

> Empty output files created for aggregation query in append mode
> ---------------------------------------------------------------
>
>                 Key: SPARK-20065
>                 URL: https://issues.apache.org/jira/browse/SPARK-20065
>             Project: Spark
>          Issue Type: Bug
>          Components: Structured Streaming
>    Affects Versions: 2.1.0
>            Reporter: Silvio Fiorito
>
> I've got a Kafka topic which I'm querying, running a windowed aggregation, with a 30 second watermark, 10 second trigger, writing out to Parquet with append output mode.
> Every 10 second trigger generates a file, regardless of whether there was any data for that trigger, or whether any records were actually finalized by the watermark.
> Is this expected behavior or should it not write out these empty files?
> {code}
> val df = spark.readStream.format("kafka")....
> val query = df
>   .withWatermark("timestamp", "30 seconds")
>   .groupBy(window($"timestamp", "10 seconds"))
>   .count()
>   .select(date_format($"window.start", "HH:mm:ss").as("time"), $"count")
> query
>   .writeStream
>   .format("parquet")
>   .option("checkpointLocation", aggChk)
>   .trigger(ProcessingTime("10 seconds"))
>   .outputMode("append")
>   .start(aggPath)
> {code}
> As the query executes, do a file listing on "aggPath" and you'll see 339 byte files at a minimum until we arrive at the first watermark and the initial batch is finalized. Even after that though, as there are empty batches it'll keep generating empty files every trigger.



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