tustvold commented on code in PR #6154:
URL: https://github.com/apache/arrow-datafusion/pull/6154#discussion_r1180501475
##########
datafusion/core/src/physical_plan/memory.rs:
##########
@@ -327,24 +326,20 @@ impl ExecutionPlan for MemoryWriteExec {
) -> Result<SendableRecordBatchStream> {
let batch_count = self.batches.len();
let data = self.input.execute(partition, context)?;
- if batch_count >= self.input.output_partitioning().partition_count() {
- // If the number of input partitions matches the number of
MemTable partitions,
- // use a lightweight implementation that doesn't utilize as many
locks.
- let table_partition = self.batches[partition].clone();
- Ok(Box::pin(MemorySinkOneToOneStream::try_new(
- table_partition,
- data,
- self.schema.clone(),
- )?))
- } else {
- // Otherwise, use the locked implementation.
- let table_partition = self.batches[partition %
batch_count].clone();
- Ok(Box::pin(MemorySinkStream::try_new(
- table_partition,
- data,
- self.schema.clone(),
- )?))
- }
+ let schema = self.schema.clone();
+ let state = (data, self.batches[partition % batch_count].clone());
+
+ let stream = futures::stream::unfold(state, |mut state| async move {
Review Comment:
We could easily hold the lock in the state if we wanted to, I just didn't
think it warranted the added complexity. You could definitely do something like
```
let stream = futures::stream::unfold(state, |mut state| async move {
let locked = state.1.write_owned().await;
loop {
let batch = match state.0.next().await {
Some(Ok(batch)) => batch,
Some(Err(e)) => return Some((Err(e), state)),
None => return None,
};
locked.push(batch)
}
});
```
Or even
```
let stream = futures::stream::unfold(state, |mut state| async move {
let locked = state.1.write().await;
loop {
let batch = match state.0.next().await {
Some(Ok(batch)) => batch,
Some(Err(e)) => {
drop(locked);
return Some((Err(e), state))
}
None => {
drop(locked);
return None
}
};
locked.push(batch)
}
});
```
Ultimately an uncontended lock is not going to matter to performance, unless
in a hot loop with no other branches
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