If you want to create a XML sitemap for a large website of lakhs of dynamic pages, then you can generate it for free, read this post how?
Here are the simple steps:
1) Click Here to go to the free sitemap generator for large dynamic website.
2) Register for free
3) Log in with your username and password
4) Add Your website where you are asked to enter your URL
5) Mark options for timestamps, priority, and frequency.
6) Now after you click on add website you will see a message Running.
7) As your website is big you will have to wait till the process is completed; once it will be done you will get a mail also you can quit the website and you can wait to get it finished.
8) After you login again you will found a message then follow the instructions and download your sitemap at your desktop.
You can also select the option to automatic update your sitemap but this feature is only available to premium or paid customers.
Happy On Page Coding :)