I'm having problems with slowness on pages that involve checkout. For some reason, it seems to me that when we wrap up the checkout session, it takes a very long time for things to "happen".
Even if logged into pages such as home or catalogsearch, the slowdown involving the session doesn't occur.
My sessions are storage on files, the same for cache. Even deactivating the profiler, slowness occurs in the same way.
I have read some similar cases using Redis (not my case, I have files) and also cases where there are many inactive sessions (also not my case, the project is not released):
There is a case where APC cache "resolved" the problem, but I belive it ins't a solution, just a workaround: https://community.magento.com/t5/Installing-Magento-1-x/Magento-very-slow-loading-since-upgrade-to-1-9-1/td-p/3930
I tried change sessions to db storage mode, but the problem persists. I got that on profiler (checkout/cart page):
Although there are many similar cases, either with session in redis, memcache or even in files, there is no concrete answer as to why this happens. So why this happens and how fix it?
I tried use Redis with Cm_RedisSession and Cm_Cache_Backend_Redis extensions but the slowness on pages that involve checkout don't stop.