Capacity Requirements

Definition

Capacity Requirement

the performance requirement that specifies a minimum required amount of the quality factor capacity

Objectives

The typical objectives of a capacity requirement are to:

• Ensure that the successful handling of the:
  • Storage of the minimum necessary number of:
    • Objects or entities.
  • Minimum necessary number of simultaneous:
    • Use case path executions.
    • Transactions.
    • Interactions with externals.
  • Interaction of the minimum necessary number of:
    • Client Externals (e.g., users, client computers).
    • Server Externals (e.g., sensors, actuators).
• Ensure that high loads are handled successfully.

Measurements

Capacity requirements are typically specified in terms of the following measurements:

• TBD.

Examples

The following are typical examples of capacity requirements:

• “The application shall successfully handle a minimum of 1.5 million customer accounts.”
• “The application shall successfully handle a minimum of 1,000 merchant accounts.”
• “The application shall successfully handle a minimum of 10,000 different products.”
• “The application shall successfully handle a minimum of 150 simultaneous customer orders including credit card authorizations.”
• “The application shall successfully handle a minimum of 100 simultaneous customer registrations 98% of the time.”
• “The application shall successfully handle a minimum of 50 simultaneous customer registrations 99.9% of the time.”
• The hotel registration system shall successfully enable the booking of reservations up to two years beyond the current date.”
• The control system shall successfully read inputs from a minimum of 1000 temperature sensors.”
• The control system shall successfully read inputs from a minimum of 500 pressure sensors.”
• The control system shall successfully control a minimum of 750 heaters.”
• The control system shall successfully control a minimum of 400 pumps.”
• The control system shall successfully control a minimum of 750 valves.”

Guidelines

The following guidelines have been found to be useful when producing capacity requirements:

• The scope of a capacity requirement can be:
  • A business enterprise
  • An application
  • A component
  • A center
• Capacity requirements can be identified and specified in term of the following:
  
  

  Component of Requirement	Possibile Values
  TBD	TBD

  
  
• Where practical, capacity requirements should be specified in terms of business domain objects or entities and not in terms of database sizes or database table volumes, which would imply a potentially unnecessary architectural constraints (e.g., a specific type of database, a specific database architecture).
• Specify the maximum expected initial load (plus a reasonable fudge factor).
• Capacity requirements have a big influence on the database and hardware architectures.
• Capacity requirements specify minimum load upon delivery. They should not be confused with:
  • Throughput requirements, which address minimum required transactions or interactions per unit time (as opposed to simultaneously).
  • Scalability requirements, which address future capacity and throughput requirements.
• Capacity requirements can be in terms of minimum average expected load as well as maximum expected load.
• Capacity requirements are typically specified using an additional “fudge factor” of 10% to 100%.
• Capacity requirements are usually tested using both load and stress testing.
• Because the minimum required capacity of the application may change over time, capacity requirements may be specified differently for different percentages of the time. Thus, capacity requirements may depend on operational availability requirements.