No, it is not zero downtime. I think that "Real Application Cluster" (RAC) databases, where multiple Oracle database instances are connected to the storage tab

No, it is not zero downtime. I think that "Real Application Cluster" (RAC) databases, where multiple Oracle database instances are connected to the storage table spaces, are able to perform a rolling upgrade, but I have not researched it in depth. I am certain that quarterly patches can be deployed in this way.