The indexer is designed for a database that deals with autoincrement index for each table. It counts the number of entries and fetches with a batch 500 entries per Id. Unfortunately Oracle deals with sequencer among all datatables. If you have e.g. 1000 entries it only fetches the entries with id 1..1000. This is a real problem with oracle databases if you import entries directly into the database. These entries will not be indexed and an manual index with go wrong.