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General: Understanding Memory - Virtual Memory Shortage Alerts

Waiting for the paging file to reach 90% threshold maybe too late, especially on any system configuration with a single paging file. Therefore, the recoemmendation is to take remedial action long before 90% threshold is reached.

When the systems reaches the 90% threshold, not only are there few available virtual memory slots, what slots are available maybe very scattered, preventing applications from allocating large blocks of virtual storage. When the system is approaching the Commit Limit, applications may begin to fail because they cannot allocate virtual memory. For instance, the system application responsible for sending the warning message to the console and to the event log that the paging file is 90% full sometimes fails because it cannot allocate virtual memory, so you might not even receive notification that the event has occurred. In short, by the time the 90% paging file allocation threshold is reached, it may already be too late to take corrective action.

A more proactive approach uses continuous performance monitoring to generate an alert when % Committed Bytes exceeds, say, a 70% threshold value. If you are operating a system above this level of virtual memory utilization consistently, it is time to explore longer-term remedial measure that might involve adding more physical memory, defining additional paging file space, or both. Computers systematically exceeding 70% - 80% Committed Bytes may suffer from serious performance degradation due to excessive demand paging activity anyway.

The above was extracted from the book, Windows 2000 Performance Guide by Mark Friedman & Odysseas Pentakalos.

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