Friday, August 16, 2013

Review - A New Design for Distributed Systems : The Remote Memory Model

What problem does the paper attack? How does it relate to and improve upon previous work in its domain?

Existing distributed systems relay on clients which has its own memory used as their virtual memory. This paper discussed about, the conventional virtual memory systems in distributed environment and the limitations of them. The paper addresses the solution for those limitations and they introduced a new design called “The remote memory model”. Also it describes the impact of remote memory model architecture for design of distributed systems.  

In existing virtual memory system architecture, each program has a large, linear address space in which it places code and data. Most conventional virtual memory systems use demand paging technique to retrieve data from secondary storage in on demand manner when system needs to access data. Existing virtual memory architecture cannot be used in distributed systems which contain diskless clients. So this paper addresses “The remote memory model” as a solution for this problem in distributed systems. 

What are the key contributions of the paper?

The main contribution of this paper is to designing remote memory model for distributed systems. Basically the remote memory model can be divided into three parts. 

  • Several client machines 
  • Various server machines, one of more dedicated machines called remote memory servers, 
  • A communication channel

In this model client machines used communication channel to access memory on the remote memory server. This model supports for heterogeneous client machines. It keep this model as general as possible. To enhance this new model from conventional systems, authors consider about following properties as well. 

  • Additional memory 
  • Arbitrarily large storage capacity 
  • Data sharing 
  • Offloading file server
  • Remote memory semantics

Communication protocol is another contribution of this paper which support for remote memory model. This protocol provides reliability, architecture independence, and efficiency along with remote memory server. Also they introduced two communication protocol layers called Xinu Paging Protocol (XPP) layer, and the Negative Acknowledgement Fragmentation Protocol (NAFP) layer.

Comments

The name of this paper is “A New Design for Distributed Systems: The Remote Memory Model”. Reading the title of this paper, reader gets an idea that this paper relevant to distributed system category. But the content of this paper did not talk anything about distributed systems. Authors did not mention any literature background about distributed systems. They entirely talked about their design model.  
  
Authors did not clearly specify the virtual memory problem in distributed systems. They just mentioned there was a problem and the remote memory model is the solution for that. But they did not comparer and prove their remote memory model is suitable for existing problems in distributed systems. They only experimented there prototype with several client machines and different kind of operating systems and showed the results. But they did not compare those results with existing systems. Also they did not talked about the communication latency with the remote memory server, because existing systems did not have such latency. Future works of this remote memory model also not mention in this paper.

References
[1] D. Comer and J. Griffioen, “A new design for distributed systems: The remote memory model,” in Proceedings of the USENIX Summer Conference, pp. 127–135, Citeseer, 1990

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