It's almost done in a streaming fashion. `xsv join` uses memory proportional to the number of records in one of the inputs and the size of the join columns in o

It's almost done in a streaming fashion. `xsv join` uses memory proportional to the number of records in one of the inputs and the size of the join columns in one of the inputs. Namely, it creates an in-memory map from the join column's values to the corresponding record index. Combined with another in-memory index that maps record index to the corresponding record's byte offset, it can jump to the corresponding record in constant time while streaming over the other input. There are better ways to do this that don't involve using this much memory, but this struck a good balance between memory usage and implementation complexity. I may improve on this some day. So basically, as long as you have enough memory to store the entire join columns along with `8 * len(one_input)` bytes for the record index, then you should be good.