Is there a join type that can pushdown join filter to one side's scan?

[alexwilcoxson-rel]

I was looking through the join options' code and it didn't look like this was possible. e.g.

LHS table produces small number of rows. Collect these and provide them as a filter pushed down to RHS scan to reduce files read.

[alamb]

To the best of my knowledge this is not supported today by DataFusion -- I think this type of filter pushdown is called "sideways information passing" in database literature and is a typical technique to improve the performance for column stores.

I think it has come up before in the context of improving join performance (for example, on the TPCH benchmarks -- cc @Dandandan and @mingmwang )

@alexwilcoxson-rel would you be willing to help file a feature request for this item? I can provide some additional commentary / pointers as well

[alexwilcoxson-rel]

thanks @alamb ! I also have a POC doing this that I can clean up and include. Will probably later today or early next week if I can get to it

[mjgarton]

Did a feature request for this even happen? I have a need for something similar.

[alexwilcoxson-rel]

https://datafusion.apache.org/blog/2025/09/10/dynamic-filters/ specifically the section about hash joins

In my case I was hoping to use it with delta-rs. I think to take advantage though some work would need to happen on the delta-rs side to take advantage of the dynamic filters

[alamb]

Note that @adriangb and @rkrishn7 are actively working on improving the filtering support:

• feat: Push down hashes to probe side in HashJoinExec #17529

[mjgarton]

Thank you for the responses @alexwilcoxson-rel and @alamb . datafusion is still mostly new to me, but your replies have got me started on learning more in the right areas.