I am using the trial version of A1 Sitemap Generator to generate sitemap for my e-commerce website with more than 50,000 pages.

However, after more than 15 hours, the program is still running and it seems like it won't finished at the meantime.

Below is the screenshot of the program.

What does it mean by the number 6656554 in the highlighted part? Is it suppose to be 0 if the scan is finished? Is it suppose to be increasing or decreasing? Because mine is always increasing.

Moreover, what does it mean by the numbers I highlighted with blue?

How long do you think does it take to finish scanning 50,000 of pages?

Hi,

Please see help page here:
http://www.microsystools.com/products/sitemap-generator/help/website-crawl-progress-status/

The red box indicated there's still 6.5 million links left in queue

You might benefit from the suggestion listed in above help page:
un-checking option: Scan website | Crawler engine | Default to GET for page requests
(It might make a quite big difference. A least it will most likely cut memory usage a lot.)

If you don't see options, switch off easy mode:
http://www.microsystools.com/products/sitemap-generator/help/easy-sitemap-generator-mode/

Regarding speed (where default speed is set quite low in A1SG to about 1/10 of max) and other optimization see:
http://www.microsystools.com/products/sitemap-generator/help/creating-sitemaps-large-websites/
(notice that your webserver/db may also be cause of slowness)