Question

Will I notice any loss in performance if I enable php_pdo_mysql.dll in php?

Answer 1

Enabling an extension will not change much to the way PHP works :

• there will be one more file loaded when PHP starts (negligible, considering the amount of files your application is made of — and a file loaded often will be kept in RAM by the OS)
• there will be a couple of C function executed when a request starts and stops ; but those generally don’t do much (especially, because hurting performances is not the goal)
• considering you probably have database queries and stuff like that, the performance “degradation” introduced by loading one more extension will be negligible

So, no, you will not notice anything ; ne need to worry 🙂

What really matters, actually, is what that new extension can bring you ; if it can bring you anything good (and PDO generally can 😉 ), then, don’t hesitate even one second !

(Well, maybe if you were serving hundreds millions of requests each day, using hundreds of servers, you might notice a small difference — but that’s probably not your case 😉 )