In Hivemall, `each_top_k` is useful for practical use cases. On the other hand, there are some cases we need to join tables then compute Top-K entries.You know we can compute this query by using regular joins + `each_top_k`. However, we have space to improve this query more; that is, we compute Top-K entries while processing joins. This optimization avoids a substantial amount of I/O for joins.
An example query is as follows;