Dandandan commented on PR #15380:
URL: https://github.com/apache/datafusion/pull/15380#issuecomment-2803478057
> > Thanks for sharing the results @zhuqi-lucas this is really interesting!
> > I think it mainly shows that we probably should try and use more
efficient in memory sorting (e.g. an arrow kernel that sorts multiple batches)
here rather than use `SortPreservingMergeStream` which is intended to be used
on data streams. The arrow kernel would avoid the regressions of `concat`.
>
> I think the SortPreservingMergeStream is about as efficient as we know how
to make it
>
> Maybe we can look into what overhead makes concat'ing better 🤔 Any
per-stream overhead we can improve in SortPreservingMergeStream would likely
flow directly to any query that does sorts
Perhaps SortPreservingMergeStream can be optimized for the cases all
partitions are exhausted / all batches of all partitions are in memory, so it
doesn't need to deal with the `cursor` complexity and can use Rust quicksort on
the remaining data...
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