If you’re looking at performance and you want to get some quick wins, the obvious place to start is caching. Caching as a concept is focused exclusively around improving performance. It’s been used in disk controllers, processors, and other hardware devices since nearly the beginning of computing. Various software methods have been devised to do caching as well. Fundamentally caching has one limitation — managing updates — and several decisions. In this article, we’ll explore the basic options for caching and their impact on performance.

Cache Updates

Caching replaces slower operations—like making calls to a SQL server to an instantiate an object—with faster operations like reading a serialized copy of the object from memory. This can dramatically improve the performance of reading the object; however, what happens when the object changes from time to time? Take, for instance, a common scenario where the user has a cart of products. It’s normal, and encouraged, for the user to change what’s in their shopping cart. However, if you’re displaying a quick summary of the items in a user’s cart on each page, it may not be something that you want to read from the database each time.

That’s where managing cache updates comes in, you have to decide how to manage these updates and still have a cache. At the highest level you have two different strategies. The first set of strategies is a synchronized approach where it’s important to maintain synchronization of the object at all times. The second strategy is a lazy (or time) based updating strategy where having a completely up-to-date object is nice but not essential. Say for instance that you had an update to a product’s description to include a new award the product has won — that may not be essential to know about immediately in the application.

Read More at http://www.developer.com/design/article.php/3831821