Why is it only 3-4 times faster is what surprises me. No question that cutting out the PHP interpreter and VM is going to speed things up, but only ever so slightly?
The speed of MySQL is constant in both cases, and IO is always expensive, thus the CPU speedup via C vs PHP is not as dramatic as one hopes; remove MySQL from the equation and you'll see the gigantic difference.
Because it's taken out of the context. Original text says:
"We even observed that ngx_drizzle + ngx_rds_json achieved 128MB/sec (Yes, 1024Mbit/sec!) for a 380KB data-set query while connecting to a simple mysql server, about 3 ~ 4 times as fast as php + libmysql in this setting."
As you can imagine in such scenario (380KB result), MySQL engine is taking the most of the time.
