I'm currently working on a social web application using python/django. Recently I heard about the PHP's weakness on large scale projects, and how hippo-php helped Facebook to overcome this barrier. Considering a python social web application with lot of utilization, could you please tell me if a similar custom tool could help this python application? In what way? I mean which portion (or layer) of application need to be written for example in c++? I know that it's a general question but someone with relevant experience I think that could help me.
Thank you in advance.
You can think about PostgreSQL as Oracle, so from what I've found on the internet (because I am also a beginner) here is the order of DBs from smaller projects, to biggest:

SQLite
MySql
PostgreSQL
Oracle
Python/Django - Web Application Performance