Faceting and sorting might require a large amount of RAM memory for large volumes of documents. For sorting or faceting, Solr needs to un-invert the values in the index and keep such information in memory—in the field cache. This might require a significant amount of memory when your data is large enough. Of course, you can scale out, have more nodes, and spread the collection among them so that a single Solr instance is put under less pressure. However, Lucene introduced a special structure called doc values, which can work as fast as field cache, but doesn't require as much memory. This recipe will show you how to use this.