Pull Scheduling Systems

In contrast to a push scheduling system, in a pull-based system, Figure 1.6, the clients initiate the data transfer by sending requests on demand, which the server schedules to satisfy. The server accumulates the client's requests for less-popular items in the pull queue. Subsequently, an item from the pull queue is selected depending on specific selection criteria. This selection criteria depends on the specification and objective of the system. Most request first (MRF), stretch-optimal, priority, or a combination of these techniques is often used. Figure 1.7 shows an example of a pull server.

Web Container

EJB Container

Tomcat Web Server






n b





Database Enterprise Information System

Database Enterprise Information System e r r o o'

FIGURE 1.7 Example of pull server.

Data Items


FIGURE 1.8 Disadvantage of push-based system.

Data Items

High Demand ¡J Medium Demand I I Low Demand


FIGURE 1.8 Disadvantage of push-based system.

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