How frequently Googlebot fetch sitemaps? Is it depending on PageRank?

Question

How much frequently Google fetches sitemaps?

I am now working with a high traffic website normally have 30 new posts per minute but currently it provides sitemaps which links to new 100 posts (3 minutes).

1. Is this method is enough? Is bots fetch sitemaps every 3 minutes?

2. Did need to change sitemaps to list all 5M posts(indexed sitemaps)? How this change will effect on traffic and PageRank?

3. Is Googlebot remove URLs that previously listed on sitemaps but not now?

Answer 1

1. 3mins is absolutely fine, you should check to see how often Google is reading the sitemap I bet its much longer than that.
2. You should break down your sitemaps into segments and have the main sitemap link to the others as this becomes easier to manage and Google has a better time processing smaller sitemaps.
3. Google will only remove the urls if they are removed psychically. Your find that it lists more than what your sitemap has but not vice versa.