Amol Nayate

Application specific data replication for edge services

The emerging edge services architecture promises to improve the availability and performance of web services by replicating servers at geographically distributed sites. A key challenge in such systems is data replication and consistency so that edge server code can manipulate shared data without incurring the availability and performance penalties that would be incurred by accessing a traditional centralized database. This paper explores using a distributed object architecture to build an edge service system for an e-commerce application, an online bookstore represented by the TPC-W benchmark. We take advantage of application specific semantics to design distributed objects to manage a specific subset of shared information using simple and effective consistency models. Our experimental results show that by slightly relaxing consistency within individual distributed objects, we can build an edge service system that is highly available and efficient. For example, in one experiment we find that our object-based edge server system provides a factor of five improvement in response time over a traditional centralized cluster architecture and a factor of nine improvement over an edge service system that distributes code but retains a centralized database.

Improving availability and performance with application-specific data replication

The emerging edge services architecture promises to improve the availability and performance of Web services by replicating servers at geographically distributed sites. A key challenge in such systems is data replication and consistency, so that edge server code can manipulate shared data without suffering the availability and performance penalties that would be incurred by accessing a traditional centralized database. This work explores using a distributed object architecture to build an edge service data replication system for an e-commerce application, the TPC-W benchmark, which simulates an online bookstore. We take advantage of application-specific semantics to design distributed objects that each manages a specific subset of shared information using simple and effective consistency models. Our experimental results show that by slightly relaxing consistency within individual distributed objects, our application realizes both high availability and excellent performance. For example, in one experiment, we find that our object-based edge server system provides five times better response time over a traditional centralized cluster architecture and a factor of nine improvement over an edge service system that distributes code but retains a centralized database.

Resource management for scalable disconnected access to Web services

Disconnected operation, in which a client accesses a service without relying on network connectivity, is crucial for improving availability, supporting mobility, and providing responsive performance. Because many web services are not cachable, disconnected access to web services may require mobile service code to execute in client caches. Unfortunately, (a) this code is untrusted, (b) this code may have nearly limitless resource demands due to prefetching, and (c) a large number of competing code modules must coexist. Thus, resource management is a key problem both for preventing denial of service attacks and for providing good performance across many services. This paper addresses the feasibility of meeting the resource management needs of an environment where service code is shipped to clients, proxies, or content distribution intermediaries. It rst examines the requirements of such a system and then develops a resource-management strategy to meet these requirements by (a) providing isolation across services to prevent denial of service attacks, (b) automatically providing appropriate allocations to di erent services to provide good global performance, and (c) requiring no hand tuning across a wide range of system con gurations and workloads.

Transparent information dissemination

This paper describes Transparent Replication through Invalidation and Prefetching (TRIP), a self tuning data replication middleware system that enables transparent replication of large-scale information dissemination services. The TRIP middleware is a key building block for constructing information dissemination services, a class of services where updates occur at an origin server and reads occur at a number of replicas; examples information dissemination services include content distribution networks such as Akamai [1] and IBMs Sport and Event replication system [2]. Furthermore, the TRIP middleware can be used to build key parts of general applications that distribute content such as file systems, distributed databases, and publish-subscribe systems.Our data replication middleware supports transparent replication by providing two crucial properties: (1) sequential consistency to avoid introducing anomalous behavior to increasingly complex services and (2) self-tuning transmission of updates to maximize performance and availability given available system resources. Our analysis of simulations and our evaluation of a prototype support the hypothesis that it is feasible to provide transparent replication for dissemination services. For example, in simulations, our systems performance is a factor of three to four faster than a demand-based middleware system for a wide range of configurations.