[GitHub] paul-rogers commented on a change in pull request #1623: DRILL-7006: Add type conversion to row writers

[GitBox <gi...@apache.org>]

paul-rogers commented on a change in pull request #1623: DRILL-7006: Add type conversion to row writers
URL: https://github.com/apache/drill/pull/1623#discussion_r251661749
 
 

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 File path: exec/java-exec/src/main/java/org/apache/drill/exec/record/metadata/PrimitiveColumnMetadata.java
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 @@ -23,16 +23,53 @@
 import org.apache.drill.common.types.Types;
 import org.apache.drill.exec.expr.TypeHelper;
 import org.apache.drill.exec.record.MaterializedField;
+import org.apache.drill.exec.vector.accessor.ColumnConversionFactory;
 
 /**
  * Primitive (non-map) column. Describes non-nullable, nullable and
  * array types (which differ only in mode, but not in metadata structure.)
+ * <p>
+ * Metadata is of two types:
+ * <ul>
+ * <li>Storage metadata that describes how the is materialized in a
+ * vector. Storage metadata is immutable because revising an existing
+ * vector is a complex operation.</li>
+ * <li>Supplemental metadata used when reading or writing the column.
+ * Supplemental metadata can be changed after the column is created,
+ * though it should generally be set before invoking code that uses
+ * the metadata.</li>
+ * </ul>
  */
 
 public class PrimitiveColumnMetadata extends AbstractColumnMetadata {
 
+  /**
+   * Expected (average) width for variable-width columns.
+   */
+
   private int expectedWidth;
 
+  /**
+   * Default value to use for filling a vector when no real data is
+   * available, such as for columns added in new files but which does not
+   * exist in existing files. The "default default" is null, which works
 
 Review comment:
   Done

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