From 6959c5ba23c9756265eefe9e64a2d2f6d93d9873 Mon Sep 17 00:00:00 2001
From: Gang Wu <ustcwg@gmail.com>
Date: Fri, 17 Jan 2025 00:00:43 +0800
Subject: [PATCH] GH-45283: [C++][Parquet] Omit level histogram when max level
 is 0

---
 cpp/src/parquet/column_writer.cc        |  3 +++
 cpp/src/parquet/size_statistics.cc      | 32 +++++++++++++++++--------
 cpp/src/parquet/size_statistics_test.cc | 18 ++++++++++++++
 3 files changed, 43 insertions(+), 10 deletions(-)

diff --git a/cpp/src/parquet/column_writer.cc b/cpp/src/parquet/column_writer.cc
index 683a5ab735aed..4998e6f301a00 100644
--- a/cpp/src/parquet/column_writer.cc
+++ b/cpp/src/parquet/column_writer.cc
@@ -1609,6 +1609,9 @@ class TypedColumnWriterImpl : public ColumnWriterImpl, public TypedColumnWriter<
 
     auto add_levels = [](std::vector<int64_t>& level_histogram,
                          ::arrow::util::span<const int16_t> levels, int16_t max_level) {
+      if (max_level == 0) {
+        return;
+      }
       ARROW_DCHECK_EQ(static_cast<size_t>(max_level) + 1, level_histogram.size());
       ::parquet::UpdateLevelHistogram(levels, level_histogram);
     };
diff --git a/cpp/src/parquet/size_statistics.cc b/cpp/src/parquet/size_statistics.cc
index 7292f9222a684..2be1828625921 100644
--- a/cpp/src/parquet/size_statistics.cc
+++ b/cpp/src/parquet/size_statistics.cc
@@ -64,14 +64,19 @@ void SizeStatistics::IncrementUnencodedByteArrayDataBytes(int64_t value) {
 }
 
 void SizeStatistics::Validate(const ColumnDescriptor* descr) const {
-  if (repetition_level_histogram.size() !=
-      static_cast<size_t>(descr->max_repetition_level() + 1)) {
-    throw ParquetException("Repetition level histogram size mismatch");
-  }
-  if (definition_level_histogram.size() !=
-      static_cast<size_t>(descr->max_definition_level() + 1)) {
-    throw ParquetException("Definition level histogram size mismatch");
-  }
+  auto validate_histogram = [](const std::vector<int64_t>& histogram, int16_t max_level,
+                               const std::string& name) {
+    if (max_level == 0 && histogram.empty()) {
+      return;
+    }
+    if (histogram.size() != static_cast<size_t>(max_level + 1)) {
+      throw ParquetException(name + " level histogram size mismatch");
+    }
+  };
+  validate_histogram(repetition_level_histogram, descr->max_repetition_level(),
+                     "Repetition");
+  validate_histogram(definition_level_histogram, descr->max_definition_level(),
+                     "Definition");
   if (unencoded_byte_array_data_bytes.has_value() &&
       descr->physical_type() != Type::BYTE_ARRAY) {
     throw ParquetException("Unencoded byte array data bytes does not support " +
@@ -93,8 +98,15 @@ void SizeStatistics::Reset() {
 
 std::unique_ptr<SizeStatistics> SizeStatistics::Make(const ColumnDescriptor* descr) {
   auto size_stats = std::make_unique<SizeStatistics>();
-  size_stats->repetition_level_histogram.resize(descr->max_repetition_level() + 1, 0);
-  size_stats->definition_level_histogram.resize(descr->max_definition_level() + 1, 0);
+  // If the max level is 0, the level histogram can be omitted because it contains
+  // only single level (a.k.a. 0) and its count is equivalent to `num_values` of the
+  // column chunk or data page.
+  if (descr->max_repetition_level() != 0) {
+    size_stats->repetition_level_histogram.resize(descr->max_repetition_level() + 1, 0);
+  }
+  if (descr->max_definition_level() != 0) {
+    size_stats->definition_level_histogram.resize(descr->max_definition_level() + 1, 0);
+  }
   if (descr->physical_type() == Type::BYTE_ARRAY) {
     size_stats->unencoded_byte_array_data_bytes = 0;
   }
diff --git a/cpp/src/parquet/size_statistics_test.cc b/cpp/src/parquet/size_statistics_test.cc
index 0958ae4dec2ca..ee2b79daabf3b 100644
--- a/cpp/src/parquet/size_statistics_test.cc
+++ b/cpp/src/parquet/size_statistics_test.cc
@@ -376,4 +376,22 @@ TEST_F(SizeStatisticsRoundTripTest, LargePage) {
                                                         /*byte_array_bytes=*/{90000}}));
 }
 
+TEST_F(SizeStatisticsRoundTripTest, MaxLevelZero) {
+  auto schema =
+      ::arrow::schema({::arrow::field("a", ::arrow::utf8(), /*nullable=*/false)});
+  WriteFile(SizeStatisticsLevel::PageAndColumnChunk,
+            ::arrow::TableFromJSON(schema, {R"([["foo"],["bar"]])"}),
+            /*max_row_group_length=*/2,
+            /*page_size=*/1024);
+  ReadSizeStatistics();
+  EXPECT_THAT(row_group_stats_,
+              ::testing::ElementsAre(SizeStatistics{/*def_levels=*/{},
+                                                    /*rep_levels=*/{},
+                                                    /*byte_array_bytes=*/6}));
+  EXPECT_THAT(page_stats_,
+              ::testing::ElementsAre(PageSizeStatistics{/*def_levels=*/{},
+                                                        /*rep_levels=*/{},
+                                                        /*byte_array_bytes=*/{6}}));
+}
+
 }  // namespace parquet