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https://issues.apache.org/jira/browse/SPARK-32456?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17179410#comment-17179410
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Apache Spark commented on SPARK-32456:
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User 'HeartSaVioR' has created a pull request for this issue:
https://github.com/apache/spark/pull/29461
> Check the Distinct by assuming it as Aggregate for Structured Streaming
> -----------------------------------------------------------------------
>
> Key: SPARK-32456
> URL: https://issues.apache.org/jira/browse/SPARK-32456
> Project: Spark
> Issue Type: Improvement
> Components: Structured Streaming
> Affects Versions: 3.0.0
> Reporter: Yuanjian Li
> Assignee: Yuanjian Li
> Priority: Major
> Fix For: 3.0.1, 3.1.0
>
>
> We want to fix 2 things here:
> 1. Give better error message for Distinct related operations in append mode
> that doesn't have a watermark
> Check the following example:
> {code:java}
> val s1 = spark.readStream.format("rate").option("rowsPerSecond",
> 1).load().createOrReplaceTempView("s1")
> val s2 = spark.readStream.format("rate").option("rowsPerSecond",
> 1).load().createOrReplaceTempView("s2")
> val unionRes = spark.sql("select s1.value , s1.timestamp from s1 union select
> s2.value, s2.timestamp from s2")
> unionResult.writeStream.option("checkpointLocation",
> ${pathA}).start(${pathB}){code}
> We'll get the following confusing exception:
> {code:java}
> java.util.NoSuchElementException: None.get
> at scala.None$.get(Option.scala:529)
> at scala.None$.get(Option.scala:527)
> at
> org.apache.spark.sql.execution.streaming.StateStoreSaveExec.$anonfun$doExecute$9(statefulOperators.scala:346)
> at
> scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
> at org.apache.spark.util.Utils$.timeTakenMs(Utils.scala:561)
> at
> org.apache.spark.sql.execution.streaming.StateStoreWriter.timeTakenMs(statefulOperators.scala:112)
> ...
> {code}
> The union clause in SQL has the requirement of deduplication, the parser will
> generate {{Distinct(Union)}} and the optimizer rule
> {{ReplaceDistinctWithAggregate}} will change it to {{Aggregate(Union)}}. So
> the root cause here is the checking logic for Aggregate is missing for
> Distinct.
> Actually it happens for all Distinct related operations in Structured
> Streaming, e.g
> {code:java}
> val df = spark.readStream.format("rate").load()
> df.createOrReplaceTempView("deduptest")
> val distinct = spark.sql("select distinct value from deduptest")
> distinct.writeStream.option("checkpointLocation",
> ${pathA}).start(${pathB}){code}
>
> 2. Make {{Distinct}} in complete mode runnable.
> The distinct in complete mode will throw the exception:
> {quote}
> {{Complete output mode not supported when there are no streaming aggregations
> on streaming DataFrames/Datasets;}}
> {quote}
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