Global variables and sessions in asp.net

Question

I'm new to web development, and coming from the world of java and android I have a few questions. (I'm using asp.net).

1. Let's assume I have a simple webpage with a label showing a number and a button. When any user presses the button, the number gets incremented automatically for all the users viewing the site, even if they do not refresh the page. Would I use sessions to achieve this or there another concept I should look into?
2. I have 2 types of counters which I store in a mysql table with the following schema.

Counter_ID Increment_Value

Each counter is active for a set amount of time and only one instance of a counter can be active at one point in time. After this time, the counter is reset to 0 and a new instance of the counter is created. I store all the instances which are active as well as past instances in a table with this schema.

Instance_ID Counter_ID Counter_Value Status(Active/Complete) Time_Remaining

When a user opens a page dedicated to one of the two counter types, the information about the current running instance of that counter needs to be loaded. Would I just execute a SQL query to achieve this and read the information for active counters every time the counter page is loaded or is there a way in which I can store this information on the site so that the site "knows" which instance is currently active and does not require an SQL query for each request (using a global variable concept) ? Obviously, the situations described above are just simplified examples which I use to explain my issue.

Answer 1

You can use ApplicationState to cache global values that are not user-specific. In your first example, since the number is incremented for all users you can transactionally store it in the database whenever it is incremented, and also cache it in ApplicationState so that it can be read quickly when rendering pages on the server. You will have to be careful to ensure you are handling concurrency properly so that each time the number is incremented the Database AND the cache are updated atomically.

It's a little unclear from your question, but if your requirement is to also publish changes to the number in real-time to all users who are currently using your website you will need to look at real-time techniques. Websockets are good for this (if available on the server and client browser). Specifically, on the .NET platform SignalR is a great way to implement real-time communication from server to client and with graceful fall-back in case WebSockets are not supported.

Just to be clear, you would not use Session storage for this scenario (unless I have misinterpreted your question). Session is per-user and should typically not affect other users in the system. Your example is all about global values so Session is not the correct choice in this case.

For your second example, using ApplicationState and transactional DB commits you should be able to cache which counter is currently active and switch them around at will provided you lock all your resources while you perform the switch between them.

Hopefully that's enough information to get you heading in the right direction.