Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/4261#discussion_r23903163
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/jdbc/JDBCRDD.scala
---
@@ -0,0 +1,417 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.jdbc
+
+import java.sql.{Connection, DatabaseMetaData, DriverManager, ResultSet,
ResultSetMetaData, SQLException}
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.{Logging, Partition, SparkContext, TaskContext}
+import org.apache.spark.rdd.RDD
+import org.apache.spark.util.NextIterator
+import org.apache.spark.sql.catalyst.analysis.HiveTypeCoercion
+import org.apache.spark.sql.catalyst.expressions.{Row, SpecificMutableRow}
+import org.apache.spark.sql.types._
+import org.apache.spark.sql.sources._
+
+private[sql] object JDBCRDD extends Logging {
+ /**
+ * Maps a JDBC type to a Catalyst type. This function is called only
when
+ * the DriverQuirks class corresponding to your database driver returns
null.
+ *
+ * @param sqlType - A field of java.sql.Types
+ * @return The Catalyst type corresponding to sqlType.
+ */
+ private def getCatalystType(sqlType: Int): DataType = {
+ val answer = sqlType match {
+ case java.sql.Types.ARRAY => null
+ case java.sql.Types.BIGINT => LongType
+ case java.sql.Types.BINARY => BinaryType
+ case java.sql.Types.BIT => BooleanType // Per JDBC; Quirks
handles quirky drivers.
+ case java.sql.Types.BLOB => BinaryType
+ case java.sql.Types.BOOLEAN => BooleanType
+ case java.sql.Types.CHAR => StringType
+ case java.sql.Types.CLOB => StringType
+ case java.sql.Types.DATALINK => null
+ case java.sql.Types.DATE => DateType
+ case java.sql.Types.DECIMAL => DecimalType.Unlimited
+ case java.sql.Types.DISTINCT => null
+ case java.sql.Types.DOUBLE => DoubleType
+ case java.sql.Types.FLOAT => FloatType
+ case java.sql.Types.INTEGER => IntegerType
+ case java.sql.Types.JAVA_OBJECT => null
+ case java.sql.Types.LONGNVARCHAR => StringType
+ case java.sql.Types.LONGVARBINARY => BinaryType
+ case java.sql.Types.LONGVARCHAR => StringType
+ case java.sql.Types.NCHAR => StringType
+ case java.sql.Types.NCLOB => StringType
+ case java.sql.Types.NULL => null
+ case java.sql.Types.NUMERIC => DecimalType.Unlimited
+ case java.sql.Types.OTHER => null
+ case java.sql.Types.REAL => DoubleType
+ case java.sql.Types.REF => StringType
+ case java.sql.Types.ROWID => LongType
+ case java.sql.Types.SMALLINT => IntegerType
+ case java.sql.Types.SQLXML => StringType
+ case java.sql.Types.STRUCT => StringType
+ case java.sql.Types.TIME => TimestampType
+ case java.sql.Types.TIMESTAMP => TimestampType
+ case java.sql.Types.TINYINT => IntegerType
+ case java.sql.Types.VARBINARY => BinaryType
+ case java.sql.Types.VARCHAR => StringType
+ case _ => null
+ }
+
+ if (answer == null) throw new SQLException("Unsupported type " +
sqlType)
+ answer
+ }
+
+ /**
+ * Takes a (schema, table) specification and returns the table's Catalyst
+ * schema.
+ *
+ * @param url - The JDBC url to fetch information from.
+ * @param table - The table name of the desired table. This may also be
a
+ * SQL query wrapped in parentheses.
+ *
+ * @return A StructType giving the table's Catalyst schema.
+ * @throws SQLException if the table specification is garbage.
+ * @throws SQLException if the table contains an unsupported type.
+ */
+ def resolveTable(url: String, table: String): StructType = {
+ val quirks = DriverQuirks.get(url)
+ val conn: Connection = DriverManager.getConnection(url)
+ try {
+ val rs = conn.prepareStatement(s"SELECT * FROM $table WHERE
1=0").executeQuery()
+ try {
+ val rsmd = rs.getMetaData
+ val ncols = rsmd.getColumnCount
+ var fields = new Array[StructField](ncols);
+ var i = 0
+ while (i < ncols) {
+ val columnName = rsmd.getColumnName(i + 1)
+ val dataType = rsmd.getColumnType(i + 1)
+ val typeName = rsmd.getColumnTypeName(i + 1)
+ val fieldSize = rsmd.getPrecision(i + 1)
+ val nullable = rsmd.isNullable(i + 1) !=
ResultSetMetaData.columnNoNulls
+ val metadata = new MetadataBuilder().putString("name",
columnName)
+ var columnType = quirks.getCatalystType(dataType, typeName,
fieldSize, metadata)
+ if (columnType == null) columnType = getCatalystType(dataType)
+ fields(i) = StructField(columnName, columnType, nullable,
metadata.build())
+ i = i + 1
+ }
+ return new StructType(fields)
+ } finally {
+ rs.close()
+ }
+ } finally {
+ conn.close()
+ }
+
+ throw new RuntimeException("This line is unreachable.")
+ }
+
+ /**
+ * Prune all but the specified columns from the specified Catalyst
schema.
+ *
+ * @param schema - The Catalyst schema of the master table
+ * @param columns - The list of desired columns
+ *
+ * @return A Catalyst schema corresponding to columns in the given order.
+ */
+ private def pruneSchema(schema: StructType, columns: Array[String]):
StructType = {
+ val fieldMap = Map(schema.fields map { x =>
x.metadata.getString("name") -> x }: _*)
+ new StructType(columns map { name => fieldMap(name) })
+ }
+
+ /**
+ * Given a driver string and an url, return a function that loads the
+ * specified driver string then returns a connection to the JDBC url.
+ * getConnector is run on the driver code, while the function it returns
+ * is run on the executor.
+ *
+ * @param driver - The class name of the JDBC driver for the given url.
+ * @param url - The JDBC url to connect to.
+ *
+ * @return A function that loads the driver and connects to the url.
+ */
+ def getConnector(driver: String, url: String): () => Connection = {
+ () => {
+ try {
+ if (driver != null) Class.forName(driver)
+ } catch {
+ case e: ClassNotFoundException => {
+ logWarning(s"Couldn't find class $driver", e);
+ }
+ }
+ DriverManager.getConnection(url)
+ }
+ }
+ /**
+ * Build and return JDBCRDD from the given information.
+ *
+ * @param sc - Your SparkContext.
+ * @param schema - The Catalyst schema of the underlying database table.
+ * @param driver - The class name of the JDBC driver for the given url.
+ * @param url - The JDBC url to connect to.
+ * @param fqTable - The fully-qualified table name (or paren'd SQL
query) to use.
+ * @param requiredColumns - The names of the columns to SELECT.
+ * @param filters - The filters to include in all WHERE clauses.
+ * @param parts - An array of JDBCPartitions specifying partition ids and
+ * per-partition WHERE clauses.
+ *
+ * @return An RDD representing "SELECT requiredColumns FROM fqTable".
+ */
+ def scanTable(sc: SparkContext,
--- End diff --
just a quick note - the spark coding style does 4 space indent for function
parameters in definitions. e.g.
```scala
def scanTable(
sc: SparkContext,
schema: StructType,
...): RDD[Row => {
```
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