From f581206a8937415018b51536d0738d615ca2fef2 Mon Sep 17 00:00:00 2001
From: mwish <maplewish117@gmail.com>
Date: Wed, 13 Dec 2023 21:25:11 +0800
Subject: [PATCH] resolve comment

---
 cpp/src/parquet/arrow/arrow_reader_writer_test.cc | 10 ++++++----
 cpp/src/parquet/arrow/writer.cc                   |  3 ++-
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/cpp/src/parquet/arrow/arrow_reader_writer_test.cc b/cpp/src/parquet/arrow/arrow_reader_writer_test.cc
index e029e13cdee6f..7094affaae16e 100644
--- a/cpp/src/parquet/arrow/arrow_reader_writer_test.cc
+++ b/cpp/src/parquet/arrow/arrow_reader_writer_test.cc
@@ -5225,6 +5225,8 @@ TEST(TestArrowReadWrite, WriteAndReadRecordBatch) {
 }
 
 TEST(TestArrowReadWrite, WriteRecordBatchNotProduceEmptyRowGroup) {
+  // GH-39211: WriteRecordBatch should prevent from writing a empty row group
+  // in the end of the file.
   auto pool = ::arrow::default_memory_pool();
   auto sink = CreateOutputStream();
   // Limit the max number of rows in a row group to 2
@@ -5247,18 +5249,18 @@ TEST(TestArrowReadWrite, WriteRecordBatchNotProduceEmptyRowGroup) {
                              &arrow_writer));
   // NewBufferedRowGroup() is not called explicitly and it will be called
   // inside WriteRecordBatch().
-  // Write 50 rows for two times
+  // Write 20 rows for two times
   for (int i = 0; i < 2; ++i) {
     auto record_batch =
-        gen.BatchOf({::arrow::field("a", ::arrow::int64())}, /*length=*/50);
+        gen.BatchOf({::arrow::field("a", ::arrow::int64())}, /*length=*/20);
     ASSERT_OK_NO_THROW(arrow_writer->WriteRecordBatch(*record_batch));
   }
   ASSERT_OK_NO_THROW(arrow_writer->Close());
   ASSERT_OK_AND_ASSIGN(auto buffer, sink->Finish());
 
   auto fileMetadata = arrow_writer->metadata();
-  EXPECT_EQ(50, fileMetadata->num_row_groups());
-  for (int i = 0; i < 50; ++i) {
+  EXPECT_EQ(20, fileMetadata->num_row_groups());
+  for (int i = 0; i < 20; ++i) {
     EXPECT_EQ(2, fileMetadata->RowGroup(i)->num_rows());
   }
 }
diff --git a/cpp/src/parquet/arrow/writer.cc b/cpp/src/parquet/arrow/writer.cc
index 1a3589ddcef9c..5238986c428d3 100644
--- a/cpp/src/parquet/arrow/writer.cc
+++ b/cpp/src/parquet/arrow/writer.cc
@@ -419,6 +419,7 @@ class FileWriterImpl : public FileWriter {
     // Max number of rows allowed in a row group.
     const int64_t max_row_group_length = this->properties().max_row_group_length();
 
+    // Initialize a new buffered row group writer if necessary.
     if (row_group_writer_ == nullptr || !row_group_writer_->buffered() ||
         row_group_writer_->num_rows() >= max_row_group_length) {
       RETURN_NOT_OK(NewBufferedRowGroup());
@@ -461,7 +462,7 @@ class FileWriterImpl : public FileWriter {
       RETURN_NOT_OK(WriteBatch(offset, batch_size));
       offset += batch_size;
 
-      // Flush current row group if it is full.
+      // Flush current row group writer and create a new writer if it is full.
       if (row_group_writer_->num_rows() >= max_row_group_length &&
           offset < batch.num_rows()) {
         RETURN_NOT_OK(NewBufferedRowGroup());