I don't understand. RecordIO doesn't support lookup of any kind; it is a linear format. The interface of Riegeli looks to me exactly like the interface to RecordIO. All they've done is removed support for Google's abstract File* storage interface so it can be used by the public.

What you are describing sounds like SSTable. Perhaps you could benefit from LevelDB.

https://www.igvita.com/2012/02/06/sstable-and-log-structured...