Cache Busting -a closer look

Cache busting

It is nothing but a technique to override caching of online advertisements. Cache busting is done primarily to stop caching of online advertisements in local system because when a previously visited page is requested again, the browser would retrieve the webpage content along with online advertisements from the cookies(refer to my earlier article on cookies ), thereby creating revenue loss to the ad serving vendors.

Why should we do cache busting?

• Absence of Cachebusting results in revenue loss to Ad server vendors , since, the already requested page along with the advert would be retrieved from the local cookies and no request would be made to 3rd part Ad server
• Lack of Cachebusting also leads to impressions discrepancies between the Publisher Ad server and the 3rd party ad server
• Improper and absence of cache busting causes 3 rd party Ad server to register impression value lesser than publisher ad server hence resulting in under delivery

How do I do Cache busting?

Cache busting can be done in 2 ways

• Using Cache busting tokens
• Implementing Math. Random() function in a JavaScript

In both the types a random number(usually 10digit) would be generated everytime an Ad is requested, so the browser actions this as a new request and delivers the Advert from Ad server and not from Cookies. This way cache busting is done.

Dealing With Cache busting Tokens

Usually all 3rd party Served Tags would contain identifiers which have to be replaced with the Publisher Ad Server Macro for cachebsuting.Look for these identifiers and replace with your Ad server's cache busting macro (value/Function) for defeating cache.

Some commonly used cache busting identifiers are

• [cachebuster]
• [TimeStamp]/[timestamp]
• [RNG]
• Insert_Time_Stamp_Here
• RANDOM

Few Caching busting Macros of leading Ad servers

Ad Server	Cache busting macro
Doubleclick's DFP	%n
Real Media OAS	%%REALRAND%%
MSN Sales's Ad Expert	##%RAND%##
Zedo	%t or %r

**Please kindly refer to your Ad server product manual for accurate macro and confirm.