Some customers utilize specific Google Analytics information included in URLs, called URL parameters or query strings, which may be generated from inside or outside the application to manage application behavior or to analyze traffic, trends, activities, or referrals. These parameters can be useful, but the high number of URL variations stored in Varnish for what is essentially a single page of content can consume far more RAM than is necessary and result in undesirable caching performance. This article explains a change Acquia is making to avoid this problem.
If you are simply using Google Analytics to track traffic, and are not processing parameters in any way, then your application will not be affected by this change. This article does not apply to you.
Currently, Acquia's platform allows HTTP requests with Google Analytics parameters to be stored in Varnish. On Monday, 11 December 2017, Acquia will implement a platform improvement that increases caching efficiency by stripping these parameters instead of storing them in Varnish. This prevents multiple variants being stored in Varnish for the same page. This will, for example, improve the cache hit rate considerably for applications that experience traffic spikes based on successful marketing campaigns.
During this maintenance, customers with applications using custom VCL files will not be impacted by this change, which will only impact customers using Acquia's default Varnish VCL configuration. If your application is using the Google Analytics script, your application should see page load performance improve as a result of this change. However, If you use PHP code or a Drupal module on your application to catch these parameters (e.g. “utm_source” and “utm_campaign”), this change will likely impact your application because these requests will stop reaching your application's web instances.
Additionally, customers using Varnish with high volume applications that have heavy reliance on Varnish caching may experience temporary performance degradation while the cache rebuilds immediately after this maintenance.