One of my friends said that a chat application,in asp.net ,they developed,they had a business layer and data layer..data layer got collection from database,and gave to business layer..now since datalayer is in a separate dll from business and web UI layer,the collection were always available to use,from any web page/business layer..is such a scenario possible? if so,why do we need cache..

I need some clarification here..how things work..in asp.net

thks

You use a cache so you don't need to reread the data from the data source. If you're after performance, you want to be able to read from a memory store right on the web server rather than from a database... typically.

Caching and collections don't have anything to do with each other. You can cache a collection or not. Caching just provides another tool to use to tune your application. Like all other tools, it needs to be used correctly and when it makes sense or could cause more harm than good.

Also, having a separate dll for the data access doesn't matter. The important thing to consider is to encapsulate your logic and layers in such a way that you can intelligently add caching as needed.

For example, in a high-performance environment, you might have strategies for certain data access. For an online store I worked on, we cached inventory information and then updated individual records in the data store and cache as inventory updates came along. We had logic built in to detect when massive inventory updates came in and would, at that point, flush the entire cache and just re-read from the data store.

thks for the answer..

but what i really wanted to know was..if my data access layer,which is a dll creates collections from database..do these collections stay in memory(web server memory)..and I can access it for any client..

thks..

Well, that really depends. They're going to stay in memory if you place them there. Again, it doesn't exactly matter if you're using a separate DLL or not, or even if you're using NHibernate or not.

NHibernate will do it's best to cache things for you. If that the default isn't enough, then turn on second-level caching with NHibernate and see if that helps. If you need more control, then implement your own caching control within your data access dll.

so by default nhibernate does use caching(first level)? how it works?