I just want to confirm whether this script was made for big websites with tens of millions of pages?

I can confirm that it will not generate a sitemap for 100 million pages, irrelevant of server size or settings. Running the script in command line also does not work.

Will there  be a future version that is capable of building sitemaps without storing data in memory until it is completed? It seems this is where the problem lies because when it reaches a certain amount of RAM, it dies and start running afresh. It never stops and never generates any files.