How do we make a large real-time search engine?

We're implementing a website which should be oriented to content and with massive access by public and we would need a search engine to index and execute queries on the indexes of contents (stored in a database, most likely MySQL InnoDB or Oracle).

The solution we found is to implement a separate service to make index constantly the contents of the database at regular intervals. Anyway, this is a complex and not optimal solution, since we would like it to index in real time and make it searchable.

Could you point me to some examples or articles I could review to design a
solution for such this context?