SolrSearch allows you to replace Omeka’s default search with Solr. Solr is a standard, popular, open source, fast text search engine server. It handles hit highlighting, date math, numeric aggregation functions (mean, max, etc.), indexing for 33 languages, replication, and many, many more things. It’s used by whitehouse.gov, Instagram, AT&T’s yp.com, Ticketmaster, and Netflix, to name a few (see the list of Public websites using Solr).
It does require running Solr as a separate server process (although possibly on the same machine), so it does require more resources—both personnel and technical—but it’s often worth the investment.