In terms of long-term planning, you have a few choices from an Oracle technology perspective that will help you keep up with the technology with minimal impact to your operations.
Oracle RAC and Planned Maintenance
We begin with a discussion of Oracle RAC. Oracle RAC is an Oracle feature based on clustering technology which provides simultaneous access to the database from every active node. This simultaneous access from live nodes is known as a “shared everything” architecture. Having “shared everything” access to your database from multiple nodes (servers), which is what Oracle RAC provides, is in many ways a boon to your database maintenance. You can apply many individual patches to the Oracle Database itself, including PSUs, in a rolling fashion by applying each patch to one node at a time. This lets you take advantage of the most critical short-term fixes without users losing access to the database.
In addition to database patches, Oracle RAC also lets you patch and even upgrade your operating system in a rolling fashion without incurring downtime. Whether you are applying a service pack (from RH4 U6 to RH4 U7, for example) or performing an actual operating system upgrade (such as an upgrade from Oracle Enterprise Linux, OEL 4 to OEL 5), it is possible to do this on a single node at a time in your Oracle RAC Cluster, without ever having to incur a full outage.
From a hardware perspective, implementing Oracle RAC also allows hardware maintenance to occur in a rolling fashion. Changes to BIOS or firmware can usually occur one node at a time, as well as replacement of individual components, either because of failure or due to an upgrade. .
Oracle Data Guard and Planned Maintenance
Although Oracle RAC is clearly a central tenet of the database grid, it is not the be-all, end-all solution to every potential need. Applying patchsets to the Oracle Database or upgrading the database from one major release to another cannot be done in a rolling fashion with Oracle RAC alone. However, by combining Oracle RAC with Oracle Data Guard, you can achieve these upgrades in a rolling fashion with minimal downtime.
Converting a physical standby database to a logical standby allows you to perform the upgrade on the logical standby while logs are still being applied from the primary (where the business is still happily chugging away using the older release). After the upgrade of the logical standby, users can be migrated to the newly upgraded system with minimal impact, and the original primary can then be upgraded—again, while log files are moving between the two sites and everything is still synchronized. After users have migrated, the original primary system can be upgraded, and users (the business) can be switched back following the same process—all with minimal, if any, impact.
Oracle RAC and Oracle Data Guard combined provide the flexibility to perform ongoing maintenance of the environment, with minimal impact to the business.
Additional Oracle Technologies
In addition to Oracle RAC and Oracle Data Guard, there are technologies such as Oracle Streams and Oracle GoldenGate to solidify the database grid.