performance and scalability

就某种算法而言：

performance 性能，可能是某算法的预测（分类）精度、耗时等指标。

scalability 可伸缩性，即规模可调整。 应用程序应对负载改变的能力，比如，一个系统在服务器于100个users和10000个users时的性能差别，如果这种差别在可以接收范围内，就说明这种系统可伸缩性强。或者系统的性能随硬件条件的增加而同步增加，基本成比例增长。如一个服务器的响应时间是100ms，四个是25ms，当然这是理想情况。它有horizontal 和vertical之分，如cluster。

衡量某算法的scalability的时候，应该是指算法应对数据样本剧增时的稳定性吧。

Scalability
In some large-scale systems, it is hard to predict the number and behavior of end users. Scalability refers to a system’s ability to support fast increasing numbers of users. The intuitive way to scale up the number of concurrent sessions handled by a server is to add resources (memory, CPU or hard disk) to it. Clustering is an alternative way to resolve the scalability issue. It allows a group of servers to share the heavy tasks, and operate as a single server logically.

from:http://hi.baidu.com/wmyqzq/blog/item/f62e398bf507201fc8fc7a00.html