Fastest way of Database Access : Caching Records in Memory

Explanation
DisplayCachedRecords() takes a single argument of number of seconds after which it will refresh the content from database. To cache data in memory it makes use of two Application level variables; cache_demo and cache_demo_date.

In the beginning of the method it retrieves cache_demo and cache_demo_date Application variable's values. cache_demo contains the in-memory list of players while cache_demo_date contains the complete date till which to keep the content cached in memory, after which it will be refreshed.

Just in case if this is the first time this method has been called after an application startup ( after computer reboot for example ), we add a new value in the datVal variable making use of DateAdd() VBScript function which adds given number of seconds in the current data.

Now we check for the difference in number of seconds between current date ( Now() ) and the date in the datVal variable.

If the difference is more than 0 then it means that the expiry time has not reached, so show the content from the cache.

If cache time has expired then we call the DisplayRecords() method again and retrieve the value into the cache_demo Application variable and set the new expiry date to current date plus given number of seconds to keep the content in memory. And then display the content to the user.

Now wasn't it simple? DisplayCachedRecords() used two Application variables, two If ... Else statements and two VBScript functions DateAdd() and DateDiff() to do the job for us.

This is it for DisplayCachedRecords() function. Now lets see how to call this function from the ASP page. Open Cache.asp page and add the following code below the two functions we already saved in it :

The only argument ( 60 ) is the number of seconds to keep the data in memory and once this time period is reached, the content is refreshed.

Above code also makes use of Timer code to determine the number of milliseconds consumed by the DisplayCachedRecords() function.

Summary
We built two functions using simple VBScript. One of which accesses the database every time it is called to retrieve a list of 17 players with their first and last names. This function was called DisplayRecords(). Then the other main function called the first function to get a list of players and saved it in an Application variable in memory. It also stored the expiry date in a separate variable in memory. This function was called DisplayCachedRecords(). Every time this function was called it will display a list of players using in-memory cache. If cache time period has expired it will refresh the data in memory by calling DisplayRecords() again.

Well this is it. I hope you found the expiry date limited cache technique useful.

Function DisplayCachedRecords(Secs)
	Dim retVal, datVal, temp1
		retVal = Application("cache_demo")
		datVal = Application("cache_demo_date")

		If datVal = "" Then
			datVal = DateAdd("s",Secs,Now)
		End If

		temp1 = DateDiff("s", Now, datVal)
			
	If temp1 > 0 And retVal <> "" Then
		DisplayCachedRecords = retVal

		' Debugging Code :
		Response.Write "<b><font color=""green"">Displaying from Cache"
		Response.Write " ... (" & temp1 & " secs remaining)</font></b>"
		Response.Write "<br><br>"
	Else

		Dim temp2
		' Change DisplayRecords() to the function whose 
		' value you want to cache
		temp2 = DisplayRecords()

		Application.Lock
			Application("cache_demo") = temp2
			Application("cache_demo_date") = DateAdd("s",Secs,Now)
		Application.UnLock

		DisplayCachedRecords = temp2

		' Debugging Code :
		Response.Write "<b><font color=""red"">Refreshing Cache ..."
		Response.Write "</font></b><br><br>"

	End If
End Function

	Dim retVal, datVal, temp1
		retVal = Application("cache_demo")
		datVal = Application("cache_demo_date")

		If datVal = "" Then
			datVal = DateAdd("s",Secs,Now)
		End If