So I have been noticing in New Relic on a lot of our sites, a lot of our long page loads are happening due to Mage_Core_Model_Session_Abstract_Varien::start. I have done some research and haven't really seen anyone else talking about this.
We use Nginx, PHP FPM, Redis for Caching and Memcache for sessions. Some of my ideas are that maybe it is something else that is taking forever and it just appears that loading the session is the problem. Or somehow there is some custom code adding a lot of data to the session causing huge sessions.
I am not that knowledgeable in terms of sessions and how they are managed, however I found some articles talking about Session locking. However I don't think that people would be opening so many pages at the same time.
Some of these loads are like 20 - 30 seconds. I am just curious if anyone else has noticed this or had more knowledge on how to analyze these types of long requests due to sessions.