Multi-version software updates

Software updates present a difficult challenge to the software maintenance process. Too often, updates result in failures, and users face the uncomfortable choice between using an old stable version which misses recent features and bug fixes, and using a new version which improves the software in certain ways, only to introduce other bugs and security vulnerabilities. In this position paper, we propose a radically new approach for performing software updates: whenever a new update becomes available, instead of upgrading the software to the new version, we instead run the new version in parallel with the old one. By carefully coordinating their executions and selecting the behavior of the more reliable version when they diverge, we can preserve the stability of the old version without giving up the features and bug fixes added to the new version. We are currently focusing on a prototype system targeting multicore CPUs, but we believe this approach could also be deployed on other parallel platforms, such as GPGPUs and cloud environments.