Write and Read Parquet Files in HDFS through Spark/Scala

51 views 0 comments last modified about 2 months ago Raymond Tang

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In my previous post, I demonstrated how to write and read parquet files in Spark/Scala. The parquet file destination is a local folder.

Write and Read Parquet Files in Spark/Scala

In this page, I am going to demonstrate how to write and read parquet files in HDFS.

Sample code

import org.apache.spark.{SparkConf, SparkContext}
import org.apache.spark.sql.{DataFrame, SQLContext}

object ParquetTest {
def main(args: Array[String]) = {
// Two threads local[2]
val conf: SparkConf = new SparkConf().setMaster("local[2]").setAppName("ParquetTest")
val sc: SparkContext = new SparkContext(conf)
val sqlContext: SQLContext = new SQLContext(sc)
writeParquet(sc, sqlContext)
readParquet(sqlContext)
}

def writeParquet(sc: SparkContext, sqlContext: SQLContext) = {
// Read file as RDD
val rdd = sqlContext.read.format("csv").option("header", "true").load("hdfs://0.0.0.0:19000/Sales.csv")
// Convert rdd to data frame using toDF; the following import is required to use toDF function.
val df: DataFrame = rdd.toDF()
// Write file to parquet
df.write.parquet("hdfs://0.0.0.0:19000/Sales.parquet");
}

def readParquet(sqlContext: SQLContext) = {
// read back parquet to DF
val newDataDF = sqlContext.read.parquet("hdfs://0.0.0.0:19000/Sales.parquet")
// show contents
newDataDF.show()
}
}

The output should be similar to the previous example.

View the parquet files in HDFS

The following command can be used to list the parquet files:

F:\DataAnalytics\hadoop-3.0.0\sbin>hdfs dfs -ls /
Found 4 items
-rw-r--r--   1 fahao supergroup        167 2018-02-26 14:42 /Sales.csv
drwxr-xr-x   - fahao supergroup          0 2018-03-17 15:44 /Sales.parquet
-rw-r--r--   1 fahao supergroup        167 2018-02-26 14:11 /Sales2.csv
-rw-r--r--   1 fahao supergroup          9 2018-02-19 22:18 /test.txt

You can also use the HDFS website portal to view it:

image

Navigate into the parquet folder:

image

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