Connectivity Model

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Connectivity Model


We divided clients and servers into clusters each containing 2 servers and 20 clients. There are 10 clusters in the system. Each client is connected to 4 servers of which 2 are ``preferred'': most accesses by this client go to these servers. A client's preferred servers are in its cluster; the non-preferred servers are chosen randomly from all the clusters. Thus, each server has 20 clients that prefer it and 20 (on average) other clients. In our experiments each server receives about 1 transaction from a non-preferred client for every 5 transactions received from preferred clients; thus non-preferred clients are not very idle from a server's point of view. Figure 3 shows a typical setup.

Figure 3: Client connections in a simulator run.

This setup models a realistic situation where clients mostly access their local server (e.g., on their LAN). To stress our scheme, we used 2 preferred servers per client instead of one: as a client switches between the 2 preferred servers, the likelihood of stalls increases due to inter-transaction dependencies created for the client by local causality. Furthermore, the connectivity of the system is high; each client has two random connections to non-preferred servers in other clusters. Thus, a client can ``spread'' the multistamp from its clusters to other clusters and vice-versa. Increase in multistamp propagation can lead to eager truncation and unnecessary stalls. We chose 10 clusters to model a system in which multistamps must be truncated; otherwise, they would contain 800 entries (since there are 800 client-server connections in the setup).

Atul Adya
Wed Jun 25 15:09:14 EDT 1997