bkietz commented on code in PR #39995:
URL: https://github.com/apache/arrow/pull/39995#discussion_r1488083820
##########
cpp/src/arrow/dataset/dataset_writer.cc:
##########
@@ -610,31 +610,34 @@ class DatasetWriter::DatasetWriterImpl {
bool will_open_file = false;
ARROW_ASSIGN_OR_RAISE(auto next_chunk, dir_queue->NextWritableChunk(
batch, &remainder,
&will_open_file));
-
- backpressure =
-
writer_state_.rows_in_flight_throttle.Acquire(next_chunk->num_rows());
- if (!backpressure.is_finished()) {
-
EVENT_ON_CURRENT_SPAN("DatasetWriter::Backpressure::TooManyRowsQueued");
- break;
- }
- if (will_open_file) {
- backpressure = writer_state_.open_files_throttle.Acquire(1);
+ // GH-39965: `NextWritableChunk` may return empty batch if file reaches
+ // `max_rows_per_file`.
+ if (next_chunk->num_rows() > 0) {
Review Comment:
Nit: I'd prefer to see this check as an independent branch rather than
nesting more deeply
```suggestion
if (next_chunk->num_rows() == 0) {
// GH-39965: `NextWritableChunk` may return an empty batch to signal
// that the current file has reached `max_rows_per_file` and should
be
// finished.
batch = std::move(remainder);
if (batch) {
RETURN_NOT_OK(dir_queue->FinishCurrentFile());
}
continue;
}
```
##########
cpp/src/arrow/dataset/dataset_writer.cc:
##########
@@ -610,31 +610,34 @@ class DatasetWriter::DatasetWriterImpl {
bool will_open_file = false;
ARROW_ASSIGN_OR_RAISE(auto next_chunk, dir_queue->NextWritableChunk(
batch, &remainder,
&will_open_file));
-
- backpressure =
-
writer_state_.rows_in_flight_throttle.Acquire(next_chunk->num_rows());
- if (!backpressure.is_finished()) {
-
EVENT_ON_CURRENT_SPAN("DatasetWriter::Backpressure::TooManyRowsQueued");
- break;
- }
- if (will_open_file) {
- backpressure = writer_state_.open_files_throttle.Acquire(1);
+ // GH-39965: `NextWritableChunk` may return empty batch if file reaches
+ // `max_rows_per_file`.
Review Comment:
IIUC:
```suggestion
// GH-39965: `NextWritableChunk` may return an empty batch to signal
// that the current file has reached `max_rows_per_file` and should be
// finished.
```
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