We have two cases, one with Oracle, and one with a test server where Reindexing doesn't seem to have any effect.
In the MySQL case, adding rows updated the index, but removing the index rows and reindexing had no effect. No errors show in the logs. No progress shows on the Home page.
In the reported Oracle case, the symptoms are similar.
+1 from customer
Reindexing to support custom provider names, fix #2921