Shared Variable Vs. Session Variable

[John Kraft]

Hi all,

My question is more of a phylisophical one here, but I am wondering what
the difference is (effectively and performance wise) between using a
shared variable/static variable and using a session variable.

I have two different applications right now that effectively perform the
same action at one point. In the one application I created a shared
variable:

shared myTable as DataTable;

In the other application I used a session variable:

session("myTable") = myTable;

Both of these ways "seem" to perform identically... that is they both
produce the same end result when I use them.

What's your view on this?

John Kraft

 

[Marina]

Shared variables are shared by every user using your web app. They last
until the web app shuts down.

Session variables are specific to a particular user. These last only for the
life of the session. If the session timeout is set to 5 minutes, after 5
minutes of inactivity the session is over, and the variable's value is gone
with it.

Session variables are going to be more costly as you are going to have a
copy of them per user.

The types of variables do not perform identially. If you have 2 people
accessing your application, they will share a copy of the Shared variable.
User1 can modify it - and User2 who accesses it afterwards sees the changes
User1 made.

With session variables, each user has their own copy of the variable, and do
not overwrite each other's changes.

 

[Cowboy \(Gregory A. Beamer\)]

Have a couple of people hit the app at the same time as you and have them
choose different variables to set up myTable. Then, you will see the
difference between Shared/static and Session.

I worked on an app where another developer set up a static function to
retrieve info. It did not manifest through the pilot, as there was not
enough activity. Put into production, users began to see cities outside of
their control, as the city was cached in a static property. Ouch!!!

If the variable is application wide, static is fine. If it gets altered on a
per user basis, you will either have to cache in a static array, or use
session. The advantage of session is it drops out when the session dies.

NOTE: Behind the scenes, in .NET, static and session are fairly similar, as
session objects are cached statically.

--
Gregory A. Beamer
MVP; MCP: +I, SE, SD, DBA

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