Editing Scalability (section)

== Universal Scalability Law ==
In [[distributed systems]], you can use [[Neil J. Gunther#Universal Scalability Law|Universal Scalability Law]] (USL) to model and to optimize scalability of your system. USL is coined by [[Neil J. Gunther]] and quantifies scalability based on parameters such as contention and coherency. Contention refers to delay due to waiting or queueing for shared resources. Coherence refers to delay for data to become consistent. For example, having a high contention indicates sequential processing that could be parallelized, while having a high coherency suggests excessive dependencies among processes, prompting you to minimize interactions. Also, with help of USL, you can, in advance, calculate the maximum effective capacity of your system: scaling up your system beyond that point is a waste. <ref>{{Cite book |last=Gunther |first=Neil |title=Guerrilla Capacity Planning: A Tactical Approach to Planning for Highly Scalable Applications and Services |year=2007 |isbn=978-3540261384}}</ref>