The Design of an Adaptahle Distributed System t

There is a need to design large database systems that are not rigid in their choice of algorithms and are responsive to faults/failures and perfor-mance degradation. To attack this challenge, we fonnalize and experiment with design principles that allow the implementation of an adaptable dis-tributed system. By adaptable, we imply that systems can be reconfigured at run-time based on perfonnance and continuity of operations require-ments and load conditions. Our research focus is on algorithms for con-currency control, resiliency to site failures, network partitioning, and failure of communication systems. The strategies for dynamic reconfiguration of the software algorithms and determining their impact are being studied both theoretically and via experiments on a prototype system called RAID being developed at Purdue. We describe a layered design for a dislributed operating system with dislributed protocols that can be modified-- or even completely changed-- while the system is run-ning. This capability will be a help in tuning the system to improve its perfonnance and reliability. In addition, the increased flexibility of this design makes it suitable for diverse applications. and capable of incor-porating new distributed systems technology as it becomes available, unlike existing systems. 1