I have a fairly large WordPress site, with almost 50,000 posts.
That might explain why I can’t build Relevanssi’s index. I’ve tried it multiple times, scaled our server… nothing works. It just takes me to a blank page after a few minutes.
First of all, there’s no way you can ever build index of that size with one go – it’s just not going to happen, unless you use Relevanssi Premium and build it from the command line with WP CLI. It’s bound to blank out, no matter what: the server will time out or run out of memory.
That’s why there’s the “Continue indexing” button. Once the page blanks out, you need to reload and click “Continue indexing”, and Relevanssi will be able continue from where it left.
With 50.000 posts, that’s going to be a painful process with lots of waiting and clicking. With Relevanssi Premium and WP CLI, it’s much easier, but will still take quite a bit of time.
However, with 50.000 posts, I would suggest you look into other search products: Solr, ElasticSearch, Swiftype or Algolia. Even when you manage to build the index, the performance of the search will not be satisfactory. Relevanssi is simply not built for numbers that big. You’ll be much happier with another search engine.