Design Principles and Optimizations for High Performance ORBs

The Internet Inter-ORB Protocol (IIOP) enables heterogeneous CORBA-compliant Object Request Brokers (ORBs) to interoperate over TCP/IP networks. The IIOP uses the Common Data Representation transfer syntax to map CORBA Interface Definition Language (IDL) data types into a portable network format. Due to the excessive marshaling/demarshaling overhead, data copying, and high-levels of function call overhead, conventional implementations of IIOP protocols have yielded relatively poor performance over high-speed networks. To meet the demands of emerging distributed multimedia applications, however, CORBAcompliant ORBs must support interoperable and highly efficient IIOP implementations. In addition, real-time ORB’s must provide efficient and predictable demultiplexing of incoming requests. This paper describes the design principles and optimizations we are using to develop a high-performance implementation of CORBA called The ACE ORB (TAO). We provide two contributions to the study and design of highperformance, real-time CORBA endsystems. First, we empirically demonstrate the benefits of systematically applying protocol optimizations to a public domain implementation of IIOP from SunSoft. These optimizations include: optimizing for the common case; eliminating gratuitous waste; replacing general purpose methods with specialized, efficient ones; precomputing values; storing redundant state to speed up expensive operations; passing information between layers; and optimizing for better processor cache performance. The results of applying these optimizations to SunSoft IIOP improved its performance substantially for all data types. Second, we present an empirical study of demultiplexing strategies used by TAO’s real-time Object Adapter. This study compares the performance of (1) linear search, (2) perfect hashing, and (3) active demultiplexing for a wide range of target objects and operations.