Silvio Fiorito created SPARK-20065:
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Summary: 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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