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Google Checkout and Barclays EPDQ callback failures
Question
I am running Google Checkout or Barclays EPDQ and appear to be having intermittent problems with orders not being successfully called back. Is there a way to fix this?
Answer
When an ASP script is run, IIS (the web server) caches an execution plan for it for a period of some minutes. Consequently calling the script again soon after is much quicker than if it is called some hours after it last ran.
Because callback scripts typically don't get called very often, these can often slip out of the server's recent memory. The problem is exacerbated with Google Checkout and Barclays EPDQ because the callback goes to a proxy script, which then calls the callback. So there are potentially two points of delay.
After extensive searching of IIS, there does not appear to be any way to extend the period these pages are considered 'live' for.
However, a relatively simple fix appears to be to setup some automated system to call the google.asp or epdq.asp every 10 minutes. Although they return an error, this procedure ensures the page execution remains in server memory and that when called up, it will respond quickly.
The simplest way to call these pages regularly is to use a site uptime monitoring service (google for 'web site monitoring'). Most charge a small annual fee but will let you specify a number of URLs on your site, and the frequency you wish to poll them. We'd recommend 10 minutes.
Thanks to Andre at www.pumpkinpip.com for this suggestion.