thinkharderdev commented on code in PR #6676:
URL: https://github.com/apache/arrow-rs/pull/6676#discussion_r1896931818
##########
parquet/src/arrow/async_reader/mod.rs:
##########
@@ -660,36 +705,89 @@ where
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) ->
Poll<Option<Self::Item>> {
loop {
match &mut self.state {
- StreamState::Decoding(batch_reader) => match
batch_reader.next() {
- Some(Ok(batch)) => {
- return Poll::Ready(Some(Ok(batch)));
+ StreamState::Decoding(batch_reader) => {
+ let res: Self::Item = match batch_reader.next() {
+ Some(Ok(batch)) => Ok(batch),
+ Some(Err(e)) => {
+ self.state = StreamState::Error;
+ return
Poll::Ready(Some(Err(ParquetError::ArrowError(e.to_string()))));
+ }
+ None => {
+ self.state = StreamState::Init;
+ continue;
+ }
+ };
+
+ if !self.prefetch_row_groups
+ || self.row_groups.is_empty()
+ || self.next_reader.is_some()
+ {
+ return Poll::Ready(Some(res));
}
- Some(Err(e)) => {
- self.state = StreamState::Error;
- return
Poll::Ready(Some(Err(ParquetError::ArrowError(e.to_string()))));
+
+ let old_state = std::mem::replace(&mut self.state,
StreamState::Init);
+
+ let row_group_idx = self.row_groups.pop_front().unwrap();
// already checked that row_groups is not empty
+
+ let fut = self.read_row_group(row_group_idx);
+
+ if let StreamState::Decoding(batch_reader) = old_state {
+ self.state = StreamState::Prefetch(batch_reader, fut);
+ return Poll::Ready(Some(res));
+ } else {
+ unreachable!()
}
- None => self.state = StreamState::Init,
- },
+ }
+ StreamState::Prefetch(batch_reader, f) => {
+ let mut noop_cx =
Context::from_waker(futures::task::noop_waker_ref());
+ match f.poll_unpin(&mut noop_cx) {
Review Comment:
Yeah. I think adding that API is fine as a way to give some more control to
the user. But I would love to find a way to really implement IO prefetching.
Maybe one day I'll find the time to really sit down and work something out 😂
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