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Ahamad, Mustaque

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Author: Bhola, Sumeer Kumar ×

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1/k Phase Timestamping for Replica Consistency in Interactive Collaborative Applications

1999 , Bhola, Sumeer Kumar , Ahamad, Mustaque

Interactive Collaborative applications, such as distributed virtual environments, collaborative CAD and multi-player games, are enabled by the data being shared across distributed users. The need to support such applications in a wide-area environment, and at the same time provide fast response to users, motivates replication of this shared data. The key characteristics of this shared data include short, incremental atomic operations for modifying this data,and the application's ability to predeclare access information for these operations. This and certain other differences from conventional replicated databases, motivate a different architecture for algorithms maintaining replica consistency. The main architectural differences include a complete separation of timestamping (for consistently ordering the operations) and execution of operations, propagation of the operation itself (instead of its effect) and local commit. We describe a specific consistency algorithm which does 2 phase timestamping (analogous to 2 phase locking) by sequentially acquiring stamps for objects accessed by an operation. Then we show how to eliminate the shrink phase and reduce the grow phase by a factor of k (when an operation accesses k objects), by concurrently getting all the stamps. This new algorithm is deadlock free and does not abort any operations.

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Responsiveness and Consistency Tradeoffs in Interactive Groupware

1998 , Bhola, Sumeer Kumar , Banavar, Guruduth S. , Ahamad, Mustaque

Interactive (or Synchronous) groupware is increasingly being deployed in widely distributed environments. Users of such applications are accustomed to direct manipulation interfaces that require fast response time. The state that enables interaction among distributed users can be replicated to provide acceptable response time in the presence of high communication latencies. We describe and evaluate design choices for protocols that maintain consistency of such state. In particular, we develop workloads which model user actions, identify the metrics important from a user's viewpoint, and do detailed simulations of a number of protocols to evaluate how effective they are in meeting user requirements.

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The Design Space for Data Replication Algorithms in Interactive Groupware

1998 , Bhola, Sumeer Kumar , Ahamad, Mustaque

Interactive (Synchronous) Groupware encompasses a wide range of applications, like collaborative whiteboards, text editors, engineering CAD (Computer Aided Design), Distributed Virtual Environments, and multi-player games. A very critical requirement for all these applications is the need to share data, which can be replicated to provide better responsiveness, fault-tolerance and scalability. Despite the existence of many systems and distributed algorithms for replication in interactive groupware, there is little agreement on the shared data abstraction to provide, or on the general algorithmic approach. Similarly, there is general lack of uniformity in the terminology used to describe such algorithms. This paper attempts to rectify this situation by (1) Describing the fundamental data requirements of interactive groupware, (2) Developing a data abstraction which is appropriate for meeting these requirements, (3) Developing a general algorithmic structure and terminology to express the characteristics of algorithm instances, and (4) Classifying the algorithms proposed in the research literature.

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