Simple caching system

By Roland Mensenkamp
15 June 2001

This article shows how you can create a caching system with the use of a Application variables. Advantage of such a system is that your code will be much faster because you don't have to go to the database on every request to retrieve the data. This can improve the performance of a site 1000 x.

The function and sub-routine are really simple and flexible. You can easily use them over the entire site, simply by adding them to the file.

The function 'Check' checks if there's data in the Application variable and if it's up-to-date. It has 3 parameters:
 T_name = Application Timer name
 A_name = Application name
 T_compare = How long the application shouldn't update the cache (seconds)

The sub 'Save' is used to save the values in an Application variable. It also has 3 parameters:
 T_name = Application Timer name (name you want to give it)
 A_name = Application name (name you want to give it)
 N_value = New value that you want to save in the Application variable

Remark: Don't save objects in Session or Application variables! Certain kinds of objects give big problems (see Session overview & myths)

cachefunc.asp
<%
Function Check(T_name, A_name, T_compare)
   If Application (A_name) = ""_
   Or DateDiff("n", Application(T_name), Now()) > T_compare Then
       Check = True
   Else
       Check = False
   End If
End Function

Sub Save(T_name, A_name, N_value)
   Application.Lock
       Application(T_name) = Now()
       Application(A_name) = N_value
   Application.Unlock
End Sub
%>

page.asp
<!--#include file="Cachefunc.asp"-->
<%
'check if the var is filled or if time expired
If Check("T1", "A1", 1) Then
       'Here the value you want to save (for example: opening of DB, etc.)
       sNvalue = "With your new value"
       Call Save("T1", "A1", sNvalue)
   Else
       Response.Write Application("A1")
End If
%>

As you can see it's fairly simple, and really worth while, if performance is important to you. It only works of course when the data doesn't change constantly and it doesn't vary per user. If the users don't have to see changes immediately, then this is very handy.