Let’s make the Web faster. I perceived something that may be of interest in regards to PHP, sessions, and SEO. On at least one installation, the default HTTP headers sent by the function session_start( ) were set to disable cache. In some cases, I think these headers may not be “good for Googlebot.”
As you may know, Google made an algorithm update that takes into account many aspects of site performance, often called Page Speed. Optimizing HTTP headers is one of the checkpoints and enabling browser caching via HTTP headers is a sub-point. If Googlebot respects site performance-enhancing HTTP headers then they’ll probably also acknowledge wacky ones like the PHP session_start( ) default HTTP headers that say, “do not store a copy of this page for cache; always check with the server to see if you have the most recent copy of a page immediately before and after you request a page because this content expired back in 1981 and today is April 13, 2010.”
The perceived solution for the installation was to start sessions only on pages that needed them- instead of everywhere. Now, revisiting the topic I’ve also learned that using the session_cache_limiter( ) function to control what headers are sent may also work.