Use metadata to set column comments and encoding

README.md

@@ -335,6 +335,14 @@ data should the <tt>COPY</tt> fail.</p>
 Redshift cluster and/or don't have requirements to keep the table availability high.</p>
     </td>
  </tr>
+ <tr>
+    <td><tt>description</tt></td>
+    <td>No</td>
+    <td>No default</td>
+    <td>
+<p>A description for the table. Will be set using the SQL COMMENT command, and should show up in most query tools.
+See also the <tt>description</tt> metadata to set descriptions on individual columns.
+ </tr>
  <tr>
     <td><tt>preactions</tt></td>
     <td>No</td>
@@ -414,6 +422,14 @@ df.write
   .save()
 ```
 
+### Configuring column encoding
+
+When creating a table, this library can be configured to use a specific compression encoding on individual columns. You can use the `encoding` column metadata field to specify a compression encoding for each column (see [Amazon docs](http://docs.aws.amazon.com/redshift/latest/dg/c_Compression_encodings.html) for available encodings).
+
+### Setting descriptions on columns
+
+Redshift allows columns to have descriptions attached that should show up in most query tools (using the `COMMENT` command). You can set the `description` column metadata field to specify a description for individual columns.
+
 ## Transactional Guarantees
 
 This section describes `spark-redshift`'s transactional guarantees.

src/it/scala/com/databricks/spark/redshift/RedshiftIntegrationSuite.scala

@@ -386,6 +386,90 @@ class RedshiftIntegrationSuite extends IntegrationSuiteBase {
     }
   }
 
+  test("configuring compression on columns") {
+    val tableName = s"configuring_compression_on_columns_$randomSuffix"
+    try {
+      val metadata = new MetadataBuilder().putString("encoding", "LZO").build()
+      val schema = StructType(
+        StructField("x", StringType, metadata = metadata) :: Nil)
+      sqlContext.createDataFrame(sc.parallelize(Seq(Row("a" * 128))), schema).write
+        .format("com.databricks.spark.redshift")
+        .option("url", jdbcUrl)
+        .option("dbtable", tableName)
+        .option("tempdir", tempDir)
+        .mode(SaveMode.ErrorIfExists)
+        .save()
+      assert(DefaultJDBCWrapper.tableExists(conn, tableName))
+      val loadedDf = sqlContext.read
+        .format("com.databricks.spark.redshift")
+        .option("url", jdbcUrl)
+        .option("dbtable", tableName)
+        .option("tempdir", tempDir)
+        .load()
+      checkAnswer(loadedDf, Seq(Row("a" * 128)))
+      val encodingDF = sqlContext.read
+        .format("jdbc")
+        .option("url", jdbcUrl)
+        .option("dbtable",
+          s"""(SELECT "column", lower(encoding) FROM pg_table_def WHERE tablename='$tableName')""")
+        .load()
+      checkAnswer(encodingDF, Seq(Row("x", "lzo")))
+    } finally {
+      conn.prepareStatement(s"drop table if exists $tableName").executeUpdate()
+      conn.commit()
+    }
+  }
+
+  test("configuring comments on columns") {
+    val tableName = s"configuring_comments_on_columns_$randomSuffix"
+    try {
+      val metadata = new MetadataBuilder().putString("description", "Hello Column").build()
+      val schema = StructType(
+        StructField("x", StringType, metadata = metadata) :: Nil)
+      sqlContext.createDataFrame(sc.parallelize(Seq(Row("a" * 128))), schema).write
+        .format("com.databricks.spark.redshift")
+        .option("url", jdbcUrl)
+        .option("dbtable", tableName)
+        .option("description", "Hello Table")
+        .option("tempdir", tempDir)
+        .mode(SaveMode.ErrorIfExists)
+        .save()
+      assert(DefaultJDBCWrapper.tableExists(conn, tableName))
+      val loadedDf = sqlContext.read
+        .format("com.databricks.spark.redshift")
+        .option("url", jdbcUrl)
+        .option("dbtable", tableName)
+        .option("tempdir", tempDir)
+        .load()
+      checkAnswer(loadedDf, Seq(Row("a" * 128)))
+      val tableDF = sqlContext.read
+        .format("jdbc")
+        .option("url", jdbcUrl)
+        .option("dbtable", s"(SELECT pg_catalog.obj_description('$tableName'::regclass))")
+        .load()
+      checkAnswer(tableDF, Seq(Row("Hello Table")))
+      val commentQuery =
+        s"""
+           |(SELECT c.column_name, pgd.description
+           |FROM pg_catalog.pg_statio_all_tables st
+           |INNER JOIN pg_catalog.pg_description pgd
+           |   ON (pgd.objoid=st.relid)
+           |INNER JOIN information_schema.columns c
+           |   ON (pgd.objsubid=c.ordinal_position AND c.table_name=st.relname)
+           |WHERE c.table_name='$tableName')
+         """.stripMargin
+      val columnDF = sqlContext.read
+        .format("jdbc")
+        .option("url", jdbcUrl)
+        .option("dbtable", commentQuery)
+        .load()
+      checkAnswer(columnDF, Seq(Row("x", "Hello Column")))
+    } finally {
+      conn.prepareStatement(s"drop table if exists $tableName").executeUpdate()
+      conn.commit()
+    }
+  }
+
   test("informative error message when saving a table with string that is longer than max length") {
     val tableName = s"error_message_when_string_too_long_$randomSuffix"
     try {

src/main/scala/com/databricks/spark/redshift/Parameters.scala

@@ -205,6 +205,11 @@ private[redshift] object Parameters {
      */
     def extraCopyOptions: String = parameters.get("extracopyoptions").getOrElse("")
 
+    /**
+      * Description of the table, set using the SQL COMMENT command.
+      */
+    def description: Option[String] = parameters.get("description")
+
     /**
       * List of semi-colon separated SQL statements to run before write operations.
       * This can be useful for running DELETE operations to clean up data

src/main/scala/com/databricks/spark/redshift/RedshiftJDBCWrapper.scala

@@ -262,7 +262,12 @@ private[redshift] class JDBCWrapper {
         case _ => throw new IllegalArgumentException(s"Don't know how to save $field to JDBC")
       }
       val nullable = if (field.nullable) "" else "NOT NULL"
-      sb.append(s""", "${name.replace("\"", "\\\"")}" $typ $nullable""".trim)
+      val encoding = if (field.metadata.contains("encoding")) {
+        s"ENCODE ${field.metadata.getString("encoding")}"
+      } else {
+        ""
+      }
+      sb.append(s""", "${name.replace("\"", "\\\"")}" $typ $nullable $encoding""".trim)
     }}
     if (sb.length < 2) "" else sb.substring(2)
   }

src/main/scala/com/databricks/spark/redshift/RedshiftWriter.scala

@@ -138,6 +138,18 @@ private[redshift] class RedshiftWriter(
     }
   }
 
+  /**
+    * Generate COMMENT SQL statements for the table and columns.
+    */
+  private[redshift] def commentActions(tableComment: Option[String], schema: StructType):
+      List[String] = {
+    tableComment.toList.map(desc => s"COMMENT ON TABLE %s IS '${desc.replace("'", "''")}'") ++
+    schema.fields
+      .withFilter(f => f.metadata.contains("description"))
+      .map(f => s"""COMMENT ON COLUMN %s."${f.name.replace("\"", "\\\"")}""""
+              + s" IS '${f.metadata.getString("description").replace("'", "''")}'")
+  }
+
   /**
    * Perform the Redshift load, including deletion of existing data in the case of an overwrite,
    * and creating the table if it doesn't already exist.
@@ -161,8 +173,10 @@ private[redshift] class RedshiftWriter(
     log.info(createStatement)
     jdbcWrapper.executeInterruptibly(conn.prepareStatement(createStatement))
 
+    val preActions = commentActions(params.description, data.schema) ++ params.preActions
+
     // Execute preActions
-    params.preActions.foreach { action =>
+    preActions.foreach { action =>
       val actionSql = if (action.contains("%s")) action.format(params.table.get) else action
       log.info("Executing preAction: " + actionSql)
       jdbcWrapper.executeInterruptibly(conn.prepareStatement(actionSql))

src/test/scala/com/databricks/spark/redshift/RedshiftSourceSuite.scala

@@ -445,6 +445,41 @@ class RedshiftSourceSuite
     assert(createTableCommand === expectedCreateTableCommand)
   }
 
+  test("configuring encoding on columns") {
+    val lzoMetadata = new MetadataBuilder().putString("encoding", "LZO").build()
+    val runlengthMetadata = new MetadataBuilder().putString("encoding", "RUNLENGTH").build()
+    val schema = StructType(
+      StructField("lzo_str", StringType, metadata = lzoMetadata) ::
+        StructField("runlength_str", StringType, metadata = runlengthMetadata) ::
+        StructField("default_str", StringType) ::
+        Nil)
+    val df = testSqlContext.createDataFrame(sc.emptyRDD[Row], schema)
+    val createTableCommand =
+      DefaultRedshiftWriter.createTableSql(df, MergedParameters.apply(defaultParams)).trim
+    val expectedCreateTableCommand =
+      """CREATE TABLE IF NOT EXISTS "PUBLIC"."test_table" ("lzo_str" TEXT  ENCODE LZO,""" +
+    """ "runlength_str" TEXT  ENCODE RUNLENGTH, "default_str" TEXT)"""
+    assert(createTableCommand === expectedCreateTableCommand)
+  }
+
+  test("configuring descriptions on columns") {
+    val descriptionMetadata1 = new MetadataBuilder().putString("description", "Test1").build()
+    val descriptionMetadata2 = new MetadataBuilder().putString("description", "Test'2").build()
+    val schema = StructType(
+      StructField("first_str", StringType, metadata = descriptionMetadata1) ::
+        StructField("second_str", StringType, metadata = descriptionMetadata2) ::
+        StructField("default_str", StringType) ::
+        Nil)
+    val df = testSqlContext.createDataFrame(sc.emptyRDD[Row], schema)
+    val commentCommands =
+      DefaultRedshiftWriter.commentActions(Some("Test"), schema)
+    val expectedCommentCommands = List(
+      "COMMENT ON TABLE %s IS 'Test'",
+      "COMMENT ON COLUMN %s.\"first_str\" IS 'Test1'",
+      "COMMENT ON COLUMN %s.\"second_str\" IS 'Test''2'")
+    assert(commentCommands === expectedCommentCommands)
+  }
+
   test("Respect SaveMode.ErrorIfExists when table exists") {
     val mockRedshift = new MockRedshift(
       defaultParams("url"),