1. A database system-implemented method, comprising: retiring, by the database system, a first computing device of a cluster of computing devices for upgrading from a first current version to a first new version; dynamically holding, by the database system, a first processing request, set to be processed by the first new version, in a wait stage while the first computing device is retired to be upgraded to the first new version; continue facilitating, by the database system, uninterrupted processing of a second processing request by a second current version of a second computing device of the cluster of computing devices while the first computing device remains retired; upgrading, by the database system, the first computing device from the first current version to the first new version; selectively routing, by the database system, the first processing request from the wait stage to the first computing device such that the first processing request is processed by the first new version of the first computing device; retiring the second computing device from the cluster of computing device to be upgraded to the second new version; holding, in a second wait stage, a third processing request to be processed by the second new version of the second computing device; and selectively routing the third processing request from the second wait stage to the second computing device such that the third processing request is processed by the second new version of the second computing device.