"Did you mean ..."

[sylvinus]

As most search engines do, it would be great to add suggestions for correcting misspellings.

Let's discuss the overall implementation here!

[OriPekelman]

1. Trivial approach would be to have a big index of all Queries (with a counter). If a query has less then X results. Search Query index for queries that are close to it; (we index this one with very leniant analyzer and do the search with some fuzziness) give a big boost on the count so more common queries end up on top. This covers a couple of use-cases and is simple enough to implement.
2. We can do the same for searches with more the X results (like when a query gives you a billion documents) we then expand the search terms by again querying the "query index" and boosting for longer phrases, which should have fewer results ( https://www.elastic.co/guide/en/elasticsearch/guide/current/scoring-theory.html#field-norm ).