Scalability
From CasGroup
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alteration of the internal structure of the system. | alteration of the internal structure of the system. | ||
| - | + | == Definition == | |
Scalability can be defined formally as the capability of a system or application | Scalability can be defined formally as the capability of a system or application | ||
or product to continue to function well without performance loss under increasing | or product to continue to function well without performance loss under increasing | ||
load by adding additonal resources or instances of the system. Couloris et al. | load by adding additonal resources or instances of the system. Couloris et al. | ||
| - | [http://www.cdk4.net/] define scalability as follows: | + | [http://www.cdk4.net/] define scalability as follows: "a distributed system is ''scalable'' |
| - | if the cost of adding a user is a constant amount in terms of the resources that must be added | + | if the cost of adding a user is a constant amount in terms of the resources that must be added". |
The system can serve an increasing demand or a larger number of users by adding additional instances | The system can serve an increasing demand or a larger number of users by adding additional instances | ||
| - | or devices. The IEEE definition says it is | + | or devices. The IEEE definition says it is "the ability to grow the power or capacity of a system by adding components" [http://www.ieeetcsc.org/content/tfcc-4-1-gray.shtml]. The key scalability technique |
is just as in [[Fault Tolerance|fault tolerance]] replication: a service can be replicated at many nodes to serve a larger demand. Scalability is also related to and sometimes required for [[Load Balancing|load balancing]]. A large-scale Internet application must be parallelized and replicated to scale well. | is just as in [[Fault Tolerance|fault tolerance]] replication: a service can be replicated at many nodes to serve a larger demand. Scalability is also related to and sometimes required for [[Load Balancing|load balancing]]. A large-scale Internet application must be parallelized and replicated to scale well. | ||
| - | Werner Vogels, CTO of Amazon.com, mentions on his personal weblog: | + | Werner Vogels, CTO of Amazon.com, mentions on his personal weblog: "A service is said to be scalable |
if when we increase the resources in a system, it results in increased performance in a manner | if when we increase the resources in a system, it results in increased performance in a manner | ||
| - | proportional to resources added. | + | proportional to resources added." (see [http://www.allthingsdistributed.com/2006/03/a_word_on_scalability.html]). |
Scalability refers to the property of a system architecture which | Scalability refers to the property of a system architecture which | ||
determines the limit of the ability to grow and to scale up. | determines the limit of the ability to grow and to scale up. | ||
| - | Ken Birman gives in his article | + | Ken Birman gives in his article "Can Web Services Scale Up ?" the following definition |
| - | of a scalable system: | + | of a scalable system: "In a nutshell, a scalable system is one that can flexibly accommodate |
growth in its client base. Such systems typically run on a clustered computer | growth in its client base. Such systems typically run on a clustered computer | ||
or in a large data center and must be able to handle high loads or sudden | or in a large data center and must be able to handle high loads or sudden | ||
demand bursts and a vast number of users. They must reliably respond even | demand bursts and a vast number of users. They must reliably respond even | ||
in the event of failures or reconfiguration. Ideally, they’re self-managed and | in the event of failures or reconfiguration. Ideally, they’re self-managed and | ||
| - | automate as many routine services such as backups and component upgrades as possible | + | automate as many routine services such as backups and component upgrades as possible". |
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== Ways and Means == | == Ways and Means == | ||
