[GitHub] [arrow] mapleFU commented on a diff in pull request #36649: PARQUET-2323: [C++] Use bitmap to store pre-buffered column chunks

[via GitHub]

mapleFU commented on code in PR #36649:
URL: https://github.com/apache/arrow/pull/36649#discussion_r1267517060


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cpp/src/parquet/file_reader.cc:
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@@ -366,9 +367,13 @@ class SerializedFile : public ParquetFileReader::Contents {
     std::vector<::arrow::io::ReadRange> ranges;
     prebuffered_column_chunks_.clear();
     for (int row : row_groups) {
-      std::unordered_set<int>& prebuffered = prebuffered_column_chunks_[row];
+      std::shared_ptr<Buffer>& col_bitmap = prebuffered_column_chunks_[row];
+      int num_cols = file_metadata_->num_columns();
+      PARQUET_THROW_NOT_OK(
+          AllocateBitmap(num_cols, 
properties_.memory_pool()).Value(&col_bitmap));
+      memset(col_bitmap->mutable_data(), 0, col_bitmap->size());

Review Comment:
   nit: Would you mind use `AllocateEmptyBitmap` instead?



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