How can you optimize the website which has millions of pages?

[bpatel]

Remove duplicate pages- remove all the pages that are creating duplicate pages. Duplicate pages are not preferred by search engines and can rank you down from search positions. If needed to repeat pages with the same information always use the canonical tag.

Well, structured website navigation – Website needed to be well managed and easy to navigate to improve website performance. Think like a user point of view and create well-structured site navigation so those users need to make effort to reach on the desired page easily.

Create a good link structure – Websites with millions of pages mean lots of content so you can create a good and efficient on-page link structure to improve the relevancy of the website. Page link structure also improves page authority and the higher page authority is always given preference in search engine results. A good link structure is a must from an SEO point of view you need to relate relevant terms and search query internally.

What if there isn't much duplicate content that has to be removed?