For example, your existing application without the database may rarely exceed the limit on the number of data files that can be open simultaneously. But when you add a database, you increase the likelihood of this significantly. This is because the query processing may often require temporary tables. Also, the ORDER BY clause (used in SQL statements to sequence retrieved data) opens temporary work files. So you may find that these files cause you to reach the limit sooner. (Note that proper tuning of the query optimizer can reduce the number of temporary files required.)
When upgrading to a new version of the RDBMS, new software components may interact with your applications differently than their predecessors did. It's important to rerun your pre-installation simulations (see Guideline 4 — Plan for Growth) to determine whether your system resources are still adequate. Investigate any differences in the two simulations. You may have to make adjustments to compensate for the differences in the RDBMS versions.
Upgrading or switching to a new database may also mean that you need to modify your makefile to coordinate with the settings of the new database. You can edit your makefile manually, or use one of the editing tools distributed with Database Connectors. For more information, see the Appendix specific to the Connector interface you are using.
If you notice a change in performance with a new release of your RDBMS, keep in mind that certain database settings can have a significant effect on speed. Fine-tuning your settings can make a difference.
Several other options to help you improve performance are listed below: