Yes, "Fast cubing" = "In-Mem cubing", they are the same thing.
To enable it, you can set "kylin.cube.algorithm=inmem" in Cube's property
overwrite step, then trigger a build. But from our experience, the "layer"
cubing is a more stable algorithm for various data set and model. If your
data is small and the model is relatively simple, "inmem" will be a good
option, otherwise, "layer" is recommended.