It's not a secret that search is a major performance hit to Elgg when you reach a certain size of database and user activity. Some time ago we made the temporary decision to disable native elgg search on the community and rely on google. This didn't feel right and we really wanted to get back to having our own internal search.
It just so happened that around this time one of my clients at Arck Interactive had commissioned a custom SOLR integration for search. The original plugin was developed by Billy Gunn, refined by me, then completely rewritten for general use and released to the community.