Github user HyukjinKwon commented on a diff in the pull request: https://github.com/apache/spark/pull/20959#discussion_r183981806 --- Diff: sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/csv/CSVSuite.scala --- @@ -1279,4 +1280,72 @@ class CSVSuite extends QueryTest with SharedSQLContext with SQLTestUtils { Row("0,2013-111-11 12:13:14") :: Row(null) :: Nil ) } + + test("SPARK-23846: schema inferring touches less data if samplingRatio < 1.0") { + // Set default values for the DataSource parameters to make sure + // that whole test file is mapped to only one partition. This will guarantee + // reliable sampling of the input file. + withSQLConf( + "spark.sql.files.maxPartitionBytes" -> (128 * 1024 * 1024).toString, + "spark.sql.files.openCostInBytes" -> (4 * 1024 * 1024).toString + )(withTempPath { path => + val ds = sampledTestData.coalesce(1) + ds.write.text(path.getAbsolutePath) + + val readback = spark.read + .option("inferSchema", true).option("samplingRatio", 0.1) + .csv(path.getCanonicalPath) + assert(readback.schema == new StructType().add("_c0", IntegerType)) + }) + } + + test("SPARK-23846: usage of samplingRatio while parsing a dataset of strings") { + val ds = sampledTestData.coalesce(1) + val readback = spark.read + .option("inferSchema", true).option("samplingRatio", 0.1) + .csv(ds) + + assert(readback.schema == new StructType().add("_c0", IntegerType)) + } + + test("SPARK-23846: samplingRatio is out of the range (0, 1.0]") { + val ds = spark.range(0, 100, 1, 1).map(_.toString) + + val errorMsg0 = intercept[IllegalArgumentException] { + spark.read.option("inferSchema", true).option("samplingRatio", -1).csv(ds) + }.getMessage + assert(errorMsg0.contains("samplingRatio (-1.0) should be greater than 0")) + + val errorMsg1 = intercept[IllegalArgumentException] { + spark.read.option("inferSchema", true).option("samplingRatio", 0).csv(ds) + }.getMessage + assert(errorMsg1.contains("samplingRatio (0.0) should be greater than 0")) + + val sampled = spark.read.option("inferSchema", true).option("samplingRatio", 10).csv(ds) --- End diff -- Can we leave this case out? Looks a bit odd we test with sampling ratio more than 1. Maybe we can just leave this case out here for now.
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