Driven by the rapid hardware development of parallel CPU/GPU architectures, the authors have witnessed emerging relational query processing techniques and implementations on those parallel architectures. However, most of those implementations are not portable across different architectures, because they are usually developed from scratch and target at a specific architecture. This paper proposes a kernel-adapter based design (OmniDB), a portable yet efficient query processor on parallel CPU/GPU architectures. OmniDB attempts to develop an extensible query processing Kernel (qKernel) based on an abstract model for parallel architectures, and to leverage an architecture-specific layer (adapter) to make qKernel be aware of the target architecture.