I don't think you need to split your research time any further. IMO your free options should be Postgres vs Interbase. MySQL has too many issues like this; cf. wharris' mention of accuracy (below) and the locking issues (although your description of essentially read-only ameliorates that one somewhat). But these are symptomatic of the many design trade-offs that were made all in the name of speed and small footprint. Comparing Oracle and MySQL is, IMO, an apples-and-oranges comparison. IB, on the other hand, is much closer to Oracle functionality and design.