This should say -- for production deployments Ranger should be configured to use Solr to index the Audit data. This is the best practice for production deployments. This will be the default configuration starting with HDP 2.5 and the use of a relational data store for Ranger audit (already announced as deprecated) will not be a supported option
To add in, as a best practice, we recommend customers using HDP 2.3.x or HDP 2.4.x to configure their audits to both Solr and HDFS. HDFS destination is for long term audit storage, while Solr could be used for short term audit query from the Ranger UI. It is recommended to use a ttl (time to live) setting in Solr to ensure documents are deleted automatically after a certain period.