When upgrading Oracle in a master-master or bi-directional environment, some additional considerations may apply. This solution explores the subtleties involved.
General information.
Though replication from a higher Oracle version to a lower one is not recommended, the reverse has been commonly done. In case of bi-directional replication, some care may be required. The secondary database may be upgraded to a higher Oracle version for the time being with the assumption that the primary (trusted source) will be upgraded in due course. What needs to be kept in mind is that the role reversal (of primary and secondary) can occur in a short notice and cannot be predicted. So the best practice is to upgrade all nodes involved in a peer to peer replication at the same time when possible. If this is not feasible, then the remaining nodes should be upgraded at the first available opportunity. So the steps involved are same as they would be when upgrading Oracle in a reporting environment, except for the part where you may not want to be running dissimilar versions of Oracle indefinitely.
According to Release Notes for Shareplex:
Replication Between Different Oracle Versions
Use caution when replicating from a newer Oracle version to an older one. New object types, datatypes, and other enhancements to RDBMS functionality can make data from the new Oracle version incompatible with the earlier one. To replicate from a newer Oracle version to an earlier one, make certain that the data to be replicated is common to both versions.
Also see related solution # SOL40097 about which one of the source and target should be upgraded first.
