From b1c13e25f1af7fb120864359a36f41fc7e9dc590 Mon Sep 17 00:00:00 2001
From: "s.kyon" <251157463+skyon0522-ai@users.noreply.github.com>
Date: Sun, 18 Oct 2026 23:07:05 +0900
Subject: [PATCH] GH-3043: Ignore V1 level encodings for omitted streams

Use the existing zero reader when a column's maximum repetition or
definition level is zero. Such a column has no corresponding encoded
level stream, so its unused header encoding must not select a physical
value reader or consume value bytes.

Preserve encoding dispatch for nonzero levels and add synthetic V1
regressions for required, optional and repeated columns across two pages.

Generated-by: OpenAI Codex
---
 .../parquet/column/impl/ColumnReaderBase.java |  9 ++-
 .../column/impl/TestColumnReaderImpl.java     | 62 +++++++++++++++++++
 2 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/parquet-column/src/main/java/org/apache/parquet/column/impl/ColumnReaderBase.java b/parquet-column/src/main/java/org/apache/parquet/column/impl/ColumnReaderBase.java
index 2b3e47116c..db7c574c60 100644
--- a/parquet-column/src/main/java/org/apache/parquet/column/impl/ColumnReaderBase.java
+++ b/parquet-column/src/main/java/org/apache/parquet/column/impl/ColumnReaderBase.java
@@ -42,6 +42,7 @@
 import org.apache.parquet.column.values.RequiresPreviousReader;
 import org.apache.parquet.column.values.ValuesReader;
 import org.apache.parquet.column.values.rle.RunLengthBitPackingHybridDecoder;
+import org.apache.parquet.column.values.rle.ZeroIntegerValuesReader;
 import org.apache.parquet.io.ParquetDecodingException;
 import org.apache.parquet.io.api.Binary;
 import org.apache.parquet.io.api.PrimitiveConverter;
@@ -727,8 +728,12 @@ private void initDataReader(Encoding dataEncoding, ByteBufferInputStream in, int
   }
 
   private void readPageV1(DataPageV1 page) {
-    ValuesReader rlReader = page.getRlEncoding().getValuesReader(path, REPETITION_LEVEL);
-    ValuesReader dlReader = page.getDlEncoding().getValuesReader(path, DEFINITION_LEVEL);
+    ValuesReader rlReader = path.getMaxRepetitionLevel() == 0
+        ? new ZeroIntegerValuesReader()
+        : page.getRlEncoding().getValuesReader(path, REPETITION_LEVEL);
+    ValuesReader dlReader = path.getMaxDefinitionLevel() == 0
+        ? new ZeroIntegerValuesReader()
+        : page.getDlEncoding().getValuesReader(path, DEFINITION_LEVEL);
     this.repetitionLevelColumn = new ValuesReaderIntIterator(rlReader);
     this.definitionLevelColumn = new ValuesReaderIntIterator(dlReader);
     int valueCount = page.getValueCount();
diff --git a/parquet-column/src/test/java/org/apache/parquet/column/impl/TestColumnReaderImpl.java b/parquet-column/src/test/java/org/apache/parquet/column/impl/TestColumnReaderImpl.java
index aa0e189194..4322062004 100644
--- a/parquet-column/src/test/java/org/apache/parquet/column/impl/TestColumnReaderImpl.java
+++ b/parquet-column/src/test/java/org/apache/parquet/column/impl/TestColumnReaderImpl.java
@@ -31,6 +31,7 @@
 import org.apache.parquet.column.ColumnDescriptor;
 import org.apache.parquet.column.ColumnReader;
 import org.apache.parquet.column.Dictionary;
+import org.apache.parquet.column.Encoding;
 import org.apache.parquet.column.ParquetProperties;
 import org.apache.parquet.column.ParquetProperties.WriterVersion;
 import org.apache.parquet.column.page.DataPage;
@@ -44,6 +45,8 @@
 import org.apache.parquet.schema.MessageType;
 import org.apache.parquet.schema.MessageTypeParser;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 public class TestColumnReaderImpl {
 
@@ -188,6 +191,65 @@ public Dictionary decode(ColumnDescriptor path) {
     validateExpectedValuesAndCount(col, pageReader);
   }
 
+  @ParameterizedTest
+  @CsvSource({
+    "required, PLAIN, RLE",
+    "required, RLE, PLAIN",
+    "required, PLAIN, PLAIN",
+    "required, RLE, RLE",
+    "optional, PLAIN, RLE",
+    "repeated, RLE, RLE"
+  })
+  public void testV1AbsentLevelEncodings(String repetition, Encoding rlEncoding, Encoding dlEncoding)
+      throws Exception {
+    MessageType schema = MessageTypeParser.parseMessageType("message test { " + repetition + " double foo; }");
+    ColumnDescriptor col = schema.getColumns().get(0);
+    MemPageWriter pageWriter = new MemPageWriter();
+    ColumnWriterV1 writer = new ColumnWriterV1(
+        col,
+        pageWriter,
+        ParquetProperties.builder()
+            .withWriterVersion(PARQUET_1_0)
+            .withDictionaryEncoding(false)
+            .build());
+    for (int i = 0; i < 4; i++) {
+      writer.write(12.5 + i, (i % 2) * col.getMaxRepetitionLevel(), col.getMaxDefinitionLevel());
+      if (i % 2 == 1) {
+        writer.writePage();
+      }
+    }
+    writer.finalizeColumnChunk();
+    writer.close();
+    assertThat(pageWriter.getPages()).hasSize(2);
+    List<DataPage> pages = new ArrayList<>();
+    for (DataPage page : pageWriter.getPages()) {
+      DataPageV1 v1 = (DataPageV1) page;
+      assertThat(v1.getValueEncoding()).isEqualTo(Encoding.PLAIN);
+      if (col.getMaxDefinitionLevel() == 0) {
+        assertThat(v1.getBytes().size()).isEqualTo(2 * Double.BYTES);
+      }
+      pages.add(new DataPageV1(
+          v1.getBytes(),
+          v1.getValueCount(),
+          v1.getUncompressedSize(),
+          v1.getStatistics(),
+          rlEncoding,
+          dlEncoding,
+          v1.getValueEncoding()));
+    }
+    ColumnReader reader = new ColumnReaderImpl(
+        col,
+        new MemPageReader(4, pages.iterator(), null),
+        new PrimitiveConverter() {},
+        VersionParser.parse(Version.FULL_VERSION));
+    for (int i = 0; i < 4; i++) {
+      assertThat(reader.getCurrentRepetitionLevel()).isEqualTo((i % 2) * col.getMaxRepetitionLevel());
+      assertThat(reader.getCurrentDefinitionLevel()).isEqualTo(col.getMaxDefinitionLevel());
+      assertThat(reader.getDouble()).isEqualTo(12.5 + i);
+      reader.consume();
+    }
+  }
+
   @Test
   public void testSynchronizingLastRowV1() throws Exception {
     testSynchronizingReader(PARQUET_1_0, false);