You have more than 50k unique pages that you want indexed? I presume that you didn't create them by hand, but are running a blog, store, or something like that, to generate them. Anything of that nature will have sitemap-creation add-ons or plug-ins available, to generate the XML file upon demand. Some will do the whole site at once, and would be run on cron job every week or even every day, and others may update the XML file any time a page is added, changed, or deleted.
You should read Google's documentation and see if you will have any penalties for that many pages. If there are, you may want to think about only sitemapping certain critical pages, such as category head pages (and everything above them), ignoring lower level pages (at least, those older than a certain age). This could bring your sitemap down to a manageable size.