lidavidm commented on a change in pull request #9620:
URL: https://github.com/apache/arrow/pull/9620#discussion_r591953537
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File path: cpp/src/parquet/arrow/reader.cc
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@@ -967,6 +978,74 @@ Status FileReaderImpl::GetRecordBatchReader(const
std::vector<int>& row_groups,
return Status::OK();
}
+/// Given a file reader and a list of row groups, this is a generator of record
+/// batch vectors (where each vector is the contents of a single row group).
+class RowGroupGenerator {
+ public:
+ using Item = ::arrow::util::optional<::arrow::RecordBatchVector>;
+
+ explicit RowGroupGenerator(FileReaderImpl* self, std::vector<int> row_groups,
+ std::vector<int> column_indices)
+ : self_(self),
+ index_(0),
+ row_groups_(std::move(row_groups)),
+ column_indices_(std::move(column_indices)) {}
+
+ ::arrow::Future<Item> operator()() {
+ if (index_ >= row_groups_.size()) {
+ return ::arrow::Future<Item>::MakeFinished(::arrow::util::nullopt);
+ }
+ int row_group = row_groups_[index_++];
+ FileReaderImpl* self = self_;
+ std::vector<int> column_indices = column_indices_;
+ ARROW_ASSIGN_OR_RAISE(auto fut,
+ ::arrow::internal::GetCpuThreadPool()->Submit(
Review comment:
Yes, this is to allow for parallelism when scanning a Parquet file.
Though as I think about it, maybe this isn't necessary? We can do the
parallelism at the scan task level already.
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