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From r...@apache.org
Subject spark git commit: [SPARK-18362][SQL] Use TextFileFormat in implementation of CSVFileFormat
Date Sat, 03 Dec 2016 05:14:36 GMT
Repository: spark
Updated Branches:
  refs/heads/master c7c726595 -> 7c33b0fd0


[SPARK-18362][SQL] Use TextFileFormat in implementation of CSVFileFormat

## What changes were proposed in this pull request?

This patch significantly improves the IO / file listing performance of schema inference in
Spark's built-in CSV data source.

Previously, this data source used the legacy `SparkContext.hadoopFile` and `SparkContext.hadoopRDD`
methods to read files during its schema inference step, causing huge file-listing bottlenecks
on the driver.

This patch refactors this logic to use Spark SQL's `text` data source to read files during
this step. The text data source still performs some unnecessary file listing (since in theory
we already have resolved the table prior to schema inference and therefore should be able
to scan without performing _any_ extra listing), but that listing is much faster and takes
place in parallel. In one production workload operating over tens of thousands of files, this
change managed to reduce schema inference time from 7 minutes to 2 minutes.

A similar problem also affects the JSON file format and this patch originally fixed that as
well, but I've decided to split that change into a separate patch so as not to conflict with
changes in another JSON PR.

## How was this patch tested?

Existing unit tests, plus manual benchmarking on a production workload.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #15813 from JoshRosen/use-text-data-source-in-csv-and-json.


Project: http://git-wip-us.apache.org/repos/asf/spark/repo
Commit: http://git-wip-us.apache.org/repos/asf/spark/commit/7c33b0fd
Tree: http://git-wip-us.apache.org/repos/asf/spark/tree/7c33b0fd
Diff: http://git-wip-us.apache.org/repos/asf/spark/diff/7c33b0fd

Branch: refs/heads/master
Commit: 7c33b0fd050f3d2b08c1cfd7efbff8166832c1af
Parents: c7c7265
Author: Josh Rosen <joshrosen@databricks.com>
Authored: Fri Dec 2 21:14:34 2016 -0800
Committer: Reynold Xin <rxin@databricks.com>
Committed: Fri Dec 2 21:14:34 2016 -0800

----------------------------------------------------------------------
 .../datasources/csv/CSVFileFormat.scala         | 60 +++++++++-----------
 .../execution/datasources/csv/CSVRelation.scala |  4 +-
 2 files changed, 28 insertions(+), 36 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/spark/blob/7c33b0fd/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVFileFormat.scala
----------------------------------------------------------------------
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVFileFormat.scala
b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVFileFormat.scala
index a369115..e627f04 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVFileFormat.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVFileFormat.scala
@@ -27,10 +27,12 @@ import org.apache.hadoop.mapreduce._
 
 import org.apache.spark.TaskContext
 import org.apache.spark.rdd.RDD
-import org.apache.spark.sql.SparkSession
+import org.apache.spark.sql.{Dataset, Encoders, SparkSession}
 import org.apache.spark.sql.catalyst.InternalRow
 import org.apache.spark.sql.catalyst.util.CompressionCodecs
 import org.apache.spark.sql.execution.datasources._
+import org.apache.spark.sql.execution.datasources.text.TextFileFormat
+import org.apache.spark.sql.functions.{length, trim}
 import org.apache.spark.sql.sources._
 import org.apache.spark.sql.types._
 import org.apache.spark.util.SerializableConfiguration
@@ -52,17 +54,21 @@ class CSVFileFormat extends TextBasedFileFormat with DataSourceRegister
{
       sparkSession: SparkSession,
       options: Map[String, String],
       files: Seq[FileStatus]): Option[StructType] = {
+    require(files.nonEmpty, "Cannot infer schema from an empty set of files")
     val csvOptions = new CSVOptions(options)
 
     // TODO: Move filtering.
     val paths = files.filterNot(_.getPath.getName startsWith "_").map(_.getPath.toString)
-    val rdd = baseRdd(sparkSession, csvOptions, paths)
-    val firstLine = findFirstLine(csvOptions, rdd)
+    val lines: Dataset[String] = readText(sparkSession, csvOptions, paths)
+    val firstLine: String = findFirstLine(csvOptions, lines)
     val firstRow = new CsvReader(csvOptions).parseLine(firstLine)
     val caseSensitive = sparkSession.sessionState.conf.caseSensitiveAnalysis
     val header = makeSafeHeader(firstRow, csvOptions, caseSensitive)
 
-    val parsedRdd = tokenRdd(sparkSession, csvOptions, header, paths)
+    val parsedRdd: RDD[Array[String]] = CSVRelation.univocityTokenizer(
+      lines,
+      firstLine = if (csvOptions.headerFlag) firstLine else null,
+      params = csvOptions)
     val schema = if (csvOptions.inferSchemaFlag) {
       CSVInferSchema.infer(parsedRdd, header, csvOptions)
     } else {
@@ -173,51 +179,37 @@ class CSVFileFormat extends TextBasedFileFormat with DataSourceRegister
{
     }
   }
 
-  private def baseRdd(
-      sparkSession: SparkSession,
-      options: CSVOptions,
-      inputPaths: Seq[String]): RDD[String] = {
-    readText(sparkSession, options, inputPaths.mkString(","))
-  }
-
-  private def tokenRdd(
-      sparkSession: SparkSession,
-      options: CSVOptions,
-      header: Array[String],
-      inputPaths: Seq[String]): RDD[Array[String]] = {
-    val rdd = baseRdd(sparkSession, options, inputPaths)
-    // Make sure firstLine is materialized before sending to executors
-    val firstLine = if (options.headerFlag) findFirstLine(options, rdd) else null
-    CSVRelation.univocityTokenizer(rdd, firstLine, options)
-  }
-
   /**
    * Returns the first line of the first non-empty file in path
    */
-  private def findFirstLine(options: CSVOptions, rdd: RDD[String]): String = {
+  private def findFirstLine(options: CSVOptions, lines: Dataset[String]): String = {
+    import lines.sqlContext.implicits._
+    val nonEmptyLines = lines.filter(length(trim($"value")) > 0)
     if (options.isCommentSet) {
-      val comment = options.comment.toString
-      rdd.filter { line =>
-        line.trim.nonEmpty && !line.startsWith(comment)
-      }.first()
+      nonEmptyLines.filter(!$"value".startsWith(options.comment.toString)).first()
     } else {
-      rdd.filter { line =>
-        line.trim.nonEmpty
-      }.first()
+      nonEmptyLines.first()
     }
   }
 
   private def readText(
       sparkSession: SparkSession,
       options: CSVOptions,
-      location: String): RDD[String] = {
+      inputPaths: Seq[String]): Dataset[String] = {
     if (Charset.forName(options.charset) == StandardCharsets.UTF_8) {
-      sparkSession.sparkContext.textFile(location)
+      sparkSession.baseRelationToDataFrame(
+        DataSource.apply(
+          sparkSession,
+          paths = inputPaths,
+          className = classOf[TextFileFormat].getName
+        ).resolveRelation(checkFilesExist = false))
+        .select("value").as[String](Encoders.STRING)
     } else {
       val charset = options.charset
-      sparkSession.sparkContext
-        .hadoopFile[LongWritable, Text, TextInputFormat](location)
+      val rdd = sparkSession.sparkContext
+        .hadoopFile[LongWritable, Text, TextInputFormat](inputPaths.mkString(","))
         .mapPartitions(_.map(pair => new String(pair._2.getBytes, 0, pair._2.getLength,
charset)))
+      sparkSession.createDataset(rdd)(Encoders.STRING)
     }
   }
 

http://git-wip-us.apache.org/repos/asf/spark/blob/7c33b0fd/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVRelation.scala
----------------------------------------------------------------------
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVRelation.scala
b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVRelation.scala
index 52de11d..e4ce7a9 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVRelation.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVRelation.scala
@@ -34,12 +34,12 @@ import org.apache.spark.sql.types._
 object CSVRelation extends Logging {
 
   def univocityTokenizer(
-      file: RDD[String],
+      file: Dataset[String],
       firstLine: String,
       params: CSVOptions): RDD[Array[String]] = {
     // If header is set, make sure firstLine is materialized before sending to executors.
     val commentPrefix = params.comment.toString
-    file.mapPartitions { iter =>
+    file.rdd.mapPartitions { iter =>
       val parser = new CsvReader(params)
       val filteredIter = iter.filter { line =>
         line.trim.nonEmpty && !line.startsWith(commentPrefix)


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