useExternalMemory no longer does anything


It appears that this change:

(Unfortunately the forum seems to be snipping off the specific parts of that URL. The change I’m referring to is located at lines 788 through 822 of file src/data/

makes this parameter:


I am trying to debug memory allocation failures in a distributed xgboost4j-spark app, and one thing that comes to mind is whether SparsePageDMatrix might be worth trying as an alternative to SimpleDMatrix. I thought setting the useExternalMemory parameter might do that, but it appears that the PR above removed that functionality in 1.5.0. Could someone explain why?