Memory Used for GrouBy or Join

[hahn80]

In Apache Arrow Acero C++, group_by builds an internal aggregation map, while hash join builds an internal hash table.
How can we measure or track the memory usage specifically allocated for these two structures during execution?
Thank you!

[zanmato1984]

It’s only supported in Arrow C++ today. You can pass a dedicated MemoryPool via ExecContext for the plan and query bytes_allocated() (and max_memory() for peak). This gives a plan‑level estimate because other operators also allocate from that pool. For hash‑table‑only memory, you’d need to route allocations for SwissJoin (and/or hash aggregate) to a separate pool, which currently requires finer‑grained plumbing or instrumentation.

[hahn80]

Thank you very much for your inside. I will follow your idea to test it. I am working with CPP, so I probably track a bit deeper into what acero offers.

[zanmato1984]

Great. Let me know if you have any further questions! Thanks.