pitrou commented on issue #40068:
URL: https://github.com/apache/arrow/issues/40068#issuecomment-1944240567
Thanks! So, trying to sum it up:
* main thread has an Acero source node whose `StartProducing` calls
`FragmentsToBatches` calls `ParquetFileFormat::ScanBatchesAsync`
```
#2
arrow::dataset::ParquetFileFormat::ScanBatchesAsync(std::shared_ptr<arrow::dataset::ScanOptions>
const&, std::shared_ptr<arrow::dataset::FileFragment> const&) const
$ARROW_ROOT/cpp/src/arrow/dataset/file_parquet.cc:607:36
(arrow_reproduce+0x126e20b)
#3
arrow::dataset::FileFragment::ScanBatchesAsync(std::shared_ptr<arrow::dataset::ScanOptions>
const&) $ARROW_ROOT/cpp/src/arrow/dataset/file_base.cc:188:19
(arrow_reproduce+0x1156715)
#4 arrow::dataset::(anonymous
namespace)::FragmentToBatches(arrow::Enumerated<std::shared_ptr<arrow::dataset::Fragment>>
const&, std::shared_ptr<arrow::dataset::ScanOptions> const&)
$ARROW_ROOT/cpp/src/arrow/dataset/scanner.cc:305:3 (arrow_reproduce+0x11c4fa1)
#5 arrow::dataset::(anonymous
namespace)::FragmentsToBatches(std::function<arrow::Future<std::shared_ptr<arrow::dataset::Fragment>>
()>, std::shared_ptr<arrow::dataset::ScanOptions>
const&)::$_0::operator()(arrow::Enumerated<std::shared_ptr<arrow::dataset::Fragment>>
const&) const $ARROW_ROOT/cpp/src/arrow/dataset/scanner.cc:333:36
(arrow_reproduce+0x11c4fa1)
```
* Arrow worker thread executes a Future callback from
`ParquetFileReader::OpenAsync`'s own callback, that in turn calls
`ParquetFileFormat::ScanBatchesAsync`
```
#4
arrow::dataset::ParquetFileFragment::SetMetadata(std::shared_ptr<parquet::FileMetaData>,
std::shared_ptr<parquet::arrow::SchemaManifest>)
$ARROW_ROOT/cpp/src/arrow/dataset/file_parquet.cc:819:13
(arrow_reproduce+0x12764c2)
#5
arrow::dataset::ParquetFileFragment::EnsureCompleteMetadata(parquet::arrow::FileReader*)
$ARROW_ROOT/cpp/src/arrow/dataset/file_parquet.cc:811:10
(arrow_reproduce+0x1275b25)
#6
arrow::dataset::ParquetFileFormat::ScanBatchesAsync(std::shared_ptr<arrow::dataset::ScanOptions>
const&, std::shared_ptr<arrow::dataset::FileFragment> const&)
const::$_0::operator()(std::shared_ptr<parquet::arrow::FileReader> const&)
$ARROW_ROOT/cpp/src/arrow/dataset/file_parquet.cc:618:5
(arrow_reproduce+0x1283f68)
```
What seems weird is that two `ScanBatchesAsync` calls would happen on the
_same_ fragment.
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