Fundamentals of Capacity Management
Article 5/98
This article is the first in a series which will deal with capacity management. I was at a recent meeting of the local chapter of the Computer Measurement Group (www.CMG.org) when the attendees were asked if anyone was actually doing capacity planning at their organizations. Of the group of thirty or so professionals, across twenty or so companies, only one said that he was doing capacity planning. Amazing!
The title of this column refers to capacity "management" deliberately. Management is an ongoing process, and capacity management should be an important ongoing function at every shop. For us in the fault-tolerant OLTP arena, capacity management is critical. Our organizations have invested a lot of money to ensure that the computers continue to process through a hardware failure. However, I know lots of shops who shrug their shoulders if they have a processing problem during their peak season. "It just happens," they say. It doesn't have to.
The unfortunate thing about capacity problems is that they surface when the transaction volume is highest. A capacity-related outage has high impact on lots of transactions. It has high visibility with management. And most times it can't be fixed on the fly.
The fact is, capacity-related outages can usually be anticipated and avoided. Wouldn't it be nice to get through the peak season without being paged for a problem?
Capacity and performance are not the same thing. While the term "performance analysis" is all-inclusive, capacity analysis is a distinctly differenct discipline. Performance analysis deals primarily with the application. Its measurements are based on the transactions: throughput and response. Performance is primarily affected by the design of the application, and secondarily by the capacity issues of the OS and the platform.
Capacity management is the discipline of managing the resources used by the applications. It focuses on the computer, devices and other entities that are in the transaction path. How much CPU/disk/memory/comm are being used to process the workload? How busy are the devices and server processes? Are there enough threads for the transactions to follow? When will we run out of capacity on any entity?
If it's done properly, capacity management ensures that there will always be adequate processing power to handle the expected workload that the outside world throws at the system.
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