Many of the changes required for Ingres are backward compatible with Ingres 6.4. Make application changes in the Ingres 6.4 installation, and bring them forward to the Ingres installation for testing. In this way, you do not have to freeze application development while preparing for Ingres.

At this stage, resist the temptation to make Ingres-specific application changes. While an outer join or a session temp table may enhance performance, there is plenty of time to add performance enhancements after the upgrade.