I recently invested some of my time to watch the PHP & Oracle presentation video from the meeting which took place this month in Singapore:

If you are in the PHP business it really worth considering porting your database to Oracle 10gR2 or 11g and using oci8 as oracle datasource for your application.

Just some of the performance features you will get:
-prefetching rows (reducing round trips from web to database servers)
guidelines to follow when prefetching rows:
* don’t prefetch more data than necessary
* use SQL to process data especially analytics functions

-binding scalars
(avoiding double parsing SQL statements like SELECT * FROM USERS WHERE user_id=2 and SELECT * FROM USERS WHERE user_id=3)
A great advantage is that avoids SQL injections too!

-transactions

-PL/SQL

-array binds

-statement cache