Het is spark.mongodb.input.sampleSize
SparkSession spark = SparkSession.builder()
.master("local[2]")
.appName("SparkReadMgToHive")
.config("spark.sql.warehouse.dir", warehouseLocation)
.config("spark.mongodb.input.uri", "mongodb://localhost:27017/test.testcollection")
.config("spark.mongodb.input.sampleSize", 50000)
.enableHiveSupport()
.getOrCreate();