Re-indexing Solr collections after upgrading the cluster
After upgrading to Cloudera Runtime, your Solr collections are automatically recreated with the updated configuration, but the collections are empty. Cloudera does not support upgrading the underlying index files from CDH 5 to Cloudera Runtime, so you must re-index your collections.
Apache Solr does not have dedicated re-indexing functionality. To re-index a collection, you must perform whatever indexing procedure you initially used to index your documents.