According to the current ruby driver author, the latest driver should support back to Postgres 7.4. Any older version of postgres is unsupported by the postgres

According to the current ruby driver author, the latest driver should support back to Postgres 7.4. Any older version of postgres is unsupported by the postgres project itself, but if you really need something that old, you should be able to use the old "postgres" gem. Granted there might be driver / database / platform combinations that have issues, but if you know of one, please submit a bug report with the specifics. HTH :-)