slessard commented on code in PR #10953:
URL: https://github.com/apache/iceberg/pull/10953#discussion_r1753042474


##########
arrow/src/test/java/org/apache/iceberg/arrow/vectorized/ArrowReaderTest.java:
##########
@@ -262,6 +263,89 @@ public void testReadColumnFilter2() throws Exception {
         scan, NUM_ROWS_PER_MONTH, 12 * NUM_ROWS_PER_MONTH, 
ImmutableList.of("timestamp"));
   }
 
+  @Test
+  public void testReadColumnThatDoesNotExistInParquetSchema() throws Exception 
{
+    setMaxStackTraceElementsDisplayed(15);
+    rowsWritten = Lists.newArrayList();
+    tables = new HadoopTables();
+
+    Schema schema =
+        new Schema(
+            Types.NestedField.required(1, "a", Types.IntegerType.get()),
+            Types.NestedField.optional(2, "b", Types.IntegerType.get()));
+
+    PartitionSpec spec = PartitionSpec.builderFor(schema).build();
+    Table table1 = tables.create(schema, spec, tableLocation);
+
+    // Add one record to the table
+    GenericRecord rec = GenericRecord.create(schema);
+    rec.setField("a", 1);
+    List<GenericRecord> genericRecords = Lists.newArrayList();
+    genericRecords.add(rec);
+
+    AppendFiles appendFiles = table1.newAppend();
+    appendFiles.appendFile(writeParquetFile(table1, genericRecords));
+    appendFiles.commit();
+
+    // Alter the table schema by adding a new, optional column.
+    // Do not add any data for this new column in the one existing row in the 
table
+    // and do not insert any new rows into the table.
+    Table table = tables.load(tableLocation);
+    table.updateSchema().addColumn("z", Types.IntegerType.get()).commit();
+
+    // Select all columns, all rows from the table
+    TableScan scan = table.newScan().select("*");
+
+    List<String> columns = ImmutableList.of("a", "b", "z");
+    // Read the data and verify that the returned ColumnarBatches match 
expected rows.
+    int rowIndex = 0;
+    try (VectorizedTableScanIterable itr = new 
VectorizedTableScanIterable(scan, 1, false)) {
+      for (ColumnarBatch batch : itr) {
+        List<GenericRecord> expectedRows = rowsWritten.subList(rowIndex, 
rowIndex + 1);
+
+        Map<String, Integer> columnNameToIndex = Maps.newHashMap();
+        for (int i = 0; i < columns.size(); i++) {
+          columnNameToIndex.put(columns.get(i), i);
+        }
+        Set<String> columnSet = columnNameToIndex.keySet();
+
+        assertThat(batch.numRows()).isEqualTo(1);
+        assertThat(batch.numCols()).isEqualTo(columns.size());
+
+        checkColumnarArrayValues(
+            1,
+            expectedRows,
+            batch,
+            0,
+            columnSet,
+            "a",
+            (records, i) -> records.get(i).getField("a"),
+            ColumnVector::getInt);
+        checkColumnarArrayValues(
+            1,
+            expectedRows,
+            batch,
+            1,
+            columnSet,
+            "b",
+            (records, i) -> records.get(i).getField("b"),
+            (array, i) -> array.isNullAt(i) ? null : array.getInt(i));

Review Comment:
   @nastra This column does exist within the parquet file and its value is 
null. Can you tell me whether calling `array.isNullAt(i)` the correct way to 
read a column that contains a null value?



##########
arrow/src/test/java/org/apache/iceberg/arrow/vectorized/ArrowReaderTest.java:
##########
@@ -262,6 +263,89 @@ public void testReadColumnFilter2() throws Exception {
         scan, NUM_ROWS_PER_MONTH, 12 * NUM_ROWS_PER_MONTH, 
ImmutableList.of("timestamp"));
   }
 
+  @Test
+  public void testReadColumnThatDoesNotExistInParquetSchema() throws Exception 
{
+    setMaxStackTraceElementsDisplayed(15);
+    rowsWritten = Lists.newArrayList();
+    tables = new HadoopTables();
+
+    Schema schema =
+        new Schema(
+            Types.NestedField.required(1, "a", Types.IntegerType.get()),
+            Types.NestedField.optional(2, "b", Types.IntegerType.get()));
+
+    PartitionSpec spec = PartitionSpec.builderFor(schema).build();
+    Table table1 = tables.create(schema, spec, tableLocation);
+
+    // Add one record to the table
+    GenericRecord rec = GenericRecord.create(schema);
+    rec.setField("a", 1);
+    List<GenericRecord> genericRecords = Lists.newArrayList();
+    genericRecords.add(rec);
+
+    AppendFiles appendFiles = table1.newAppend();
+    appendFiles.appendFile(writeParquetFile(table1, genericRecords));
+    appendFiles.commit();
+
+    // Alter the table schema by adding a new, optional column.
+    // Do not add any data for this new column in the one existing row in the 
table
+    // and do not insert any new rows into the table.
+    Table table = tables.load(tableLocation);
+    table.updateSchema().addColumn("z", Types.IntegerType.get()).commit();
+
+    // Select all columns, all rows from the table
+    TableScan scan = table.newScan().select("*");
+
+    List<String> columns = ImmutableList.of("a", "b", "z");
+    // Read the data and verify that the returned ColumnarBatches match 
expected rows.
+    int rowIndex = 0;
+    try (VectorizedTableScanIterable itr = new 
VectorizedTableScanIterable(scan, 1, false)) {
+      for (ColumnarBatch batch : itr) {
+        List<GenericRecord> expectedRows = rowsWritten.subList(rowIndex, 
rowIndex + 1);
+
+        Map<String, Integer> columnNameToIndex = Maps.newHashMap();
+        for (int i = 0; i < columns.size(); i++) {
+          columnNameToIndex.put(columns.get(i), i);
+        }
+        Set<String> columnSet = columnNameToIndex.keySet();
+
+        assertThat(batch.numRows()).isEqualTo(1);
+        assertThat(batch.numCols()).isEqualTo(columns.size());
+
+        checkColumnarArrayValues(
+            1,
+            expectedRows,
+            batch,
+            0,
+            columnSet,
+            "a",
+            (records, i) -> records.get(i).getField("a"),
+            ColumnVector::getInt);
+        checkColumnarArrayValues(
+            1,
+            expectedRows,
+            batch,
+            1,
+            columnSet,
+            "b",
+            (records, i) -> records.get(i).getField("b"),
+            (array, i) -> array.isNullAt(i) ? null : array.getInt(i));
+        checkColumnarArrayValues(
+            1,
+            expectedRows,
+            batch,
+            2,
+            columnSet,
+            "z",
+            (records, i) -> records.get(i).getField("z"),
+            (array, i) -> array.isNullAt(i) ? null : array.getInt(i));

Review Comment:
   @nastra I could use your help with this line in the test. This column does 
not exist within the parquet file. (This is the very purpose for this entire 
pull request.) Currently `array.isNullAt(i)` throws a NullPointerException 
because internally `array.isNullAt(i)` calls 
`nullabilityHolder.isNullAt(rowId)` and `nullabilityHolder` is `null`. 
   
   What is the  correct way to verify that a null value is being returned for 
this column?



##########
arrow/src/main/java/org/apache/iceberg/arrow/vectorized/VectorHolder.java:
##########
@@ -140,12 +141,16 @@ public static class ConstantVectorHolder<T> extends 
VectorHolder {
     private final int numRows;
 
     public ConstantVectorHolder(int numRows) {
+      super(new NullVector("_dummy_", numRows), null, null);
       this.numRows = numRows;
       this.constantValue = null;
     }
 
     public ConstantVectorHolder(Types.NestedField icebergField, int numRows, T 
constantValue) {
-      super(icebergField);
+      super(
+          new NullVector(icebergField.name(), numRows),

Review Comment:
   I've made the change you suggested.



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