Minor: style enhancment for parquet FileMetadata Subset

mapleFU · Dec 21, 2023 · ac0c569 · ac0c569
1 parent 2308cdf
commit ac0c569
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Showing 3 changed files with 20 additions and 20 deletions.
diff --git a/cpp/src/arrow/util/bit_stream_utils.h b/cpp/src/arrow/util/bit_stream_utils.h
@@ -183,7 +183,7 @@ class BitReader {
 
   /// Returns the number of bytes left in the stream, not including the current
   /// byte (i.e., there may be an additional fraction of a byte).
-  int bytes_left() {
+  int bytes_left() const {
     return max_bytes_ -
            (byte_offset_ + static_cast<int>(bit_util::BytesForBits(bit_offset_)));
   }

diff --git a/cpp/src/parquet/metadata.cc b/cpp/src/parquet/metadata.cc
@@ -793,26 +793,19 @@ class FileMetaData::FileMetaDataImpl {
 
     std::shared_ptr<FileMetaData> out(new FileMetaData());
     out->impl_ = std::make_unique<FileMetaDataImpl>();
-    out->impl_->metadata_ = std::make_unique<format::FileMetaData>();
+    out->impl_->metadata_ = std::make_unique<format::FileMetaData>(*metadata_);
+    auto output_metadata = out->impl_->metadata_.get();
 
-    auto metadata = out->impl_->metadata_.get();
-    metadata->version = metadata_->version;
-    metadata->schema = metadata_->schema;
-
-    metadata->row_groups.resize(row_groups.size());
+    // Discard row groups that are not in the subset
+    output_metadata->num_rows = 0;
+    output_metadata->row_groups.clear();
+    output_metadata->row_groups.resize(row_groups.size());
     int i = 0;
     for (int selected_index : row_groups) {
-      metadata->num_rows += row_group(selected_index).num_rows;
-      metadata->row_groups[i++] = row_group(selected_index);
+      output_metadata->num_rows += row_group(selected_index).num_rows;
+      output_metadata->row_groups[i++] = row_group(selected_index);
     }
 
-    metadata->key_value_metadata = metadata_->key_value_metadata;
-    metadata->created_by = metadata_->created_by;
-    metadata->column_orders = metadata_->column_orders;
-    metadata->encryption_algorithm = metadata_->encryption_algorithm;
-    metadata->footer_signing_key_metadata = metadata_->footer_signing_key_metadata;
-    metadata->__isset = metadata_->__isset;
-
     out->impl_->schema_ = schema_;
     out->impl_->writer_version_ = writer_version_;
     out->impl_->key_value_metadata_ = key_value_metadata_;
@@ -886,13 +879,14 @@ std::shared_ptr<FileMetaData> FileMetaData::Make(
     const void* metadata, uint32_t* metadata_len,
     std::shared_ptr<InternalFileDecryptor> file_decryptor) {
   return std::shared_ptr<FileMetaData>(new FileMetaData(
-      metadata, metadata_len, default_reader_properties(), file_decryptor));
+      metadata, metadata_len, default_reader_properties(), std::move(file_decryptor)));
 }
 
 FileMetaData::FileMetaData(const void* metadata, uint32_t* metadata_len,
                            const ReaderProperties& properties,
                            std::shared_ptr<InternalFileDecryptor> file_decryptor)
-    : impl_(new FileMetaDataImpl(metadata, metadata_len, properties, file_decryptor)) {}
+    : impl_(new FileMetaDataImpl(metadata, metadata_len, properties,
+                                 std::move(file_decryptor))) {}
 
 FileMetaData::FileMetaData() : impl_(new FileMetaDataImpl()) {}
 
@@ -942,7 +936,7 @@ const std::string& FileMetaData::footer_signing_key_metadata() const {
 
 void FileMetaData::set_file_decryptor(
     std::shared_ptr<InternalFileDecryptor> file_decryptor) {
-  impl_->set_file_decryptor(file_decryptor);
+  impl_->set_file_decryptor(std::move(file_decryptor));
 }
 
 ParquetVersion::type FileMetaData::version() const {

diff --git a/cpp/src/parquet/metadata.h b/cpp/src/parquet/metadata.h
@@ -306,9 +306,15 @@ class PARQUET_EXPORT FileMetaData {
   int num_schema_elements() const;
 
   /// \brief The total number of rows.
+  ///
+  /// If the FileMetaData is generate from a `SubSet()`, the number of rows
+  /// will be the sum of the number of rows of remaining RowGroup.
   int64_t num_rows() const;
 
   /// \brief The number of row groups in the file.
+  ///
+  /// If the FileMetaData is generate from a `SubSet()`, the number of
+  /// row groups will be the number of remaining RowGroup.
   int num_row_groups() const;
 
   /// \brief Return the RowGroupMetaData of the corresponding row group ordinal.
@@ -338,7 +344,7 @@ class PARQUET_EXPORT FileMetaData {
   /// \brief Size of the original thrift encoded metadata footer.
   uint32_t size() const;
 
-  /// \brief Indicate if all of the FileMetadata's RowGroups can be decompressed.
+  /// \brief Indicate if all of the FileMetaData's RowGroups can be decompressed.
   ///
   /// This will return false if any of the RowGroup's page is compressed with a
   /// compression format which is not compiled in the current parquet library.