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https://issues.apache.org/jira/browse/SPARK-26745?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hyukjin Kwon resolved SPARK-26745.
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Resolution: Fixed
Assignee: Hyukjin Kwon
Fix Version/s: 3.0.0
Fixed in https://github.com/apache/spark/pull/23667
> Non-parsing Dataset.count() optimization causes inconsistent results for JSON
> inputs with empty lines
> -----------------------------------------------------------------------------------------------------
>
> Key: SPARK-26745
> URL: https://issues.apache.org/jira/browse/SPARK-26745
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.4.0, 3.0.0
> Reporter: Branden Smith
> Assignee: Hyukjin Kwon
> Priority: Blocker
> Labels: correctness
> Fix For: 3.0.0
>
>
> The optimization introduced by
> [SPARK-24959|https://issues.apache.org/jira/browse/SPARK-24959] (improving
> performance of {{{color:#0000FF}count(){color}}} for DataFrames read from
> non-multiline JSON in {{{color:#0000FF}PERMISSIVE{color}}} mode) appears to
> cause {{{color:#0000FF}count(){color}}} to erroneously include empty lines in
> its result total if run prior to JSON parsing taking place.
> For the following input:
> {code:json}
> { "a" : 1 , "b" : 2 , "c" : 3 }
> { "a" : 4 , "b" : 5 , "c" : 6 }
>
> { "a" : 7 , "b" : 8 , "c" : 9 }
> {code}
> *+Spark 2.3:+*
> {code:scala}
> scala> val df =
> spark.read.json("sql/core/src/test/resources/test-data/with-empty-line.json")
> df: org.apache.spark.sql.DataFrame = [a: bigint, b: bigint ... 1 more field]
> scala> df.count
> res0: Long = 3
> scala> df.cache.count
> res3: Long = 3
> {code}
> *+Spark 2.4:+*
> {code:scala}
> scala> val df =
> spark.read.json("sql/core/src/test/resources/test-data/with-empty-line.json")
> df: org.apache.spark.sql.DataFrame = [a: bigint, b: bigint ... 1 more field]
> scala> df.count
> res0: Long = 7
> scala> df.cache.count
> res1: Long = 3
> {code}
> Since the count is apparently updated and cached when the Jackson parser
> runs, the optimization also causes the count to appear to be unstable upon
> cache/persist operations, as shown above.
> CSV inputs, also optimized via
> [SPARK-24959|https://issues.apache.org/jira/browse/SPARK-24959], do not
> appear to be impacted by this effect.
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