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I work on a very large site with two main types of content, static landing pages for products, and a forum & blogs (user created) under each product. Site has maybe 500k - 1 million pages. We do not have a sitemap at this time.
Currently our SEO discoverability in general is good, Google is indexing new forum threads within 1-5 days roughly. Some of the "static" landing pages for our smaller, less visited products however do not have great SEO.
Question is, could our SEO be improved by creating a sitemap, and if so, how could it be implemented? I see a few ways to go about it: Sitemap includes "static" product category landing pages only - i.e., the product home pages, the forum landing pages, and blog list pages. This would probably end up being 100-200 URLs. Sitemap contains the above but is also dynamically updated with new threads & blog posts. Option 2 seems like it would mean the sitemap is unmanageably long (hundreds of thousands of forum URLs). Would a crawler even parse something that size? Or with Option 1, could it cause our organically ranked pages to change ranking due to Google re-prioritizing the pages within the sitemap?
Not a lot of information out there on this topic, appreciate any input. Thanks in advance.