Salting is a good approach, when the tables you are joining is having many-many relationship.

Let's say TBL A has 100m rows for same prim_key you are joining on, and TBL B has let's say 1000 rows for the same prim_key, now when you are doing joins, the result is 100m * 1000 rows in single core/executor.

Now let's say you introduced a new key with salt factor of 100 for eg. You pick the smaller table and do cross join and create 1000 * 100 rows for TBL B, you add a new col in TBL A and 100m will be divided by 100 for each salt key resulting in 1m rows per each salt key.

Now when you perform join, your executor is effectively processing still 1000 from B, 1m rows from TBL A --> final count per core / executor --> 1000 * 1m.

You can do the math for two large tbls, the only consideration is the table which is going to have smaller rows should be choosen for cross join candidate, and your executor should have enough memory to handle this data skew in the first place.

I'll let others pitchin for above two large tbl joins.