Cluster hash tables (CHTs) are key components of many large-scale Internet services due to their highly-scalable performance and the prevalence of the type of data they store. Another advantage of CHTs is that they can be designed to be as self-managing as a cluster of stateless servers. One key to achieving this extreme manageability is reboot-based recovery that is predictably fast and has modest impact on system performance and availability. This "cheap" recovery mechanism simplifies management in two ways. First, it simplifies failure detection by lowering the cost of acting on false positives. This enables one to use statistical techniques to turn hard-to-catch failures, such as node degradation, into failure, followed by recovery. Second, cheap recovery simplifies capacity planning by recasting repartitioning as failure plus recovery to achieve zero-downtime incremental scaling. These low-cost recovery and scaling mechanisms make it possible for the system to be continuously self-adjusting, a key property of self-managing systems.

Digital appliances designed to simplify everyday tasks are readily available to end consumers. For example, mobile users can retrieve Web content using handheld devices since content retrieval is well-supported by infrastructure services such as transformational proxies. However, the same type of support is lacking for input-centric devices, those that create content and allow users to share content. This lack of infrastructural support makes input-centric devices hard to use and less useful.The Appliance Data Services project seeks to explore a vision of an appliance computing world where users move data seamlessly among various devices. Based on this vision, we formulate three principles that guide the design of an architecture that helps realize this vision: bring devices to the forefront, minimize the number of device features, and place functionality in the network infrastructure. We evaluate our implementation of the ADS architecture based on these principles, and build applications using the ADS framework to evaluate the ease with which appliance computing applications can be built using the framework. We find that it is relatively simple to build and extend applications on ADS that make using digital devices easier, which results in the devices themselves becoming more useful.

lligent services. Our extensions are orthogonal in that they provide an interface to a service, which complements the Web browsing experience but is independent of the content of any particular site. We base our experiments on the TranSend service at UC Berkeley, which performs lossy compression on inline images to accelerate dialup Web access for a community of 25,000 subscribers. The service keeps a separate "preferences profile" for each user, which allows each user to vary the aggressiveness of lossy compression, selectively turn off the service for certain pages, and select the type of interface provided for refinement of degraded (lossily compressed) content. We are exploring three technologies for implementing the TranSend service interface: HTML decoration, Java, and JavaS- Server Client Browser Client Browser Proxy Server Server cript. The accompanying video demonstrates prototypes of all three mechanisms. We no