Wright Williams & Kelly

Factory Explorer® v2.3
Technical Alert #15

Simulating Models with Ramp Data
and Infinite Server Resource Groups


Summary: When simulating models with ramp data and one or more infinite server resource groups, Factory Explorer® asks the operating system for much more memory than is really required. The net result is longer simulation run-times, and in some cases, out-of-memory error messages on Windows 95 systems. To avoid this problem, use Windows NT systems, or modify the model to specify a large but finite number of servers (say 25) for all infinite server resource groups. This error does not affect the accuracy of any Factory Explorer® outputs. This error is fixed in Factory Explorer® v2.4 beta 2.

Details: When simulating models with ramp data, Factory Explorer® must perform housekeeping for each free server of each resource group at each ramp point (a point when something changes in the model). For models with infinite server resource groups, Factory Explorer® was mistakenly performing this housekeeping for a very large number of servers for each infinite server resource group. Part of this housekeeping involves placing an event on the simulation's future events list. Thus the future events list would grow very large, causing Factory Explorer® to repeatedly request more memory from the operating system. Although each request was generally very fast, the overall result could be a delay of several seconds at each ramp point. And for Windows 95 systems, in some cases these requests over-taxed the operating system's ability to respond, leading to an out-of-memory error. This error would occur even if the computer in question had plenty of memory. On Windows NT systems, the delay would still be present but it does not appear that the out-of-memory error would ever arise. The error does not affect the accuracy of any Factory Explorer® outputs.

Workaround: For models with infinite server resource groups and ramp data, substitute a large but finite number of servers (say 25) for infinite server resource groups, or perform all analysis on Windows NT systems.

Techalert tafx15-9805


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