mapleFU commented on code in PR #39337:
URL: https://github.com/apache/arrow/pull/39337#discussion_r1455245456
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cpp/src/parquet/metadata.cc:
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@@ -793,26 +793,29 @@ class FileMetaData::FileMetaDataImpl {
std::shared_ptr<FileMetaData> out(new FileMetaData());
out->impl_ = std::make_unique<FileMetaDataImpl>();
- out->impl_->metadata_ = std::make_unique<format::FileMetaData>();
-
- auto metadata = out->impl_->metadata_.get();
- metadata->version = metadata_->version;
- metadata->schema = metadata_->schema;
+ {
+ // GH-39336: Copy the metadata, but only the row groups we need.
+ auto temp_row_groups = std::move(this->metadata_->row_groups);
Review Comment:
The origin code don't copying the previous row-group. If we have a large
file with many row-groups (it's possible), the more around of copy waste a lot
of cpu time. So I do this as an optimization.
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