CodeIgniter or PhalconPHP ?

Have you tried HHVM? I've stayed clear because of the bad things I've heard and read about it. I don't think that's the answer. I agree good software and coding comes before hardware. That is you don't just create slow, bloated and inefficient software and mask it by chucking better hardware at it. That's not what the discussion is about. It's about whether Phalcon  will handle a million hits better than CI. And while it will, there's not going to be a massive difference, and if he's worried about that, then what will make the difference is hardware. As a site grows and gets busier, you need to upgrade and add hardware any way, and then there's the question of swapping hardware out as it gets old, which invariably means replacing it with more modern better stuff. 

I have not only tried HHVM.  I have a production environment on HHVM.  I went from CI and PHP to a micro-framework (slim) and HHVM.  The performance increase was nothing but astounding.  I was able to decrease the number of boxes needed.  

Not only this, with PHP the CPU load would go up to 100% thus maxing out the web server.  On the same hardware, HHVM never dipped below 30% CPU and had double the load. At that time, I actually ran into the database/network being the bottleneck. This was running on Amazon C type servers on a 10GB virtual network. I'm now running a different setup.

Personally, I couldnt care less about Phalcon.  To use HHVM is just replacing PHP.  No need for any c++ libraries or learning new stuff.  Your original code works.  Actually in future for advanced developers, there is talk of hacklang being optimised for HHVM thus rendering even more performance.  At which point I'll move over from phplang to hacklang and enjoy the benefits.

So the growth of the site and the acquisition of hardware pretty much run in parallel. It doesn't make a whole world of difference in that context if your application is built on top of CodeIgniter, Phalcon or HHVM. All three of them are massively slower than plain old C, which if speed really is the issue, is what you should have used in the first place. 

It doesn't. Software can be refactored. The stack can be optimised. You can move from one framework to another and get a performance increase. You can move from PHP to HHVM and get another performance increase. Later versions of software (PHP/HHVM) come out and have optimisations. With HHVM you can go from JIT checking your files every request to what's called REPO AUTH mode and getting 20% increase further. You can go from Apache to Nginx and get more increases.

Are you getting it now? On the same hardware, you can get % boosts if you know what you are doing. After that, when you throw more hardware at the problem, you are exponentially increasing those same performance gains.

Oh and one more thing. HHVM is a JIT compiler. With Repo Auth mode, its bytecode. Facebook used to convert PHP to C++. They then came out with HHVM and Hacklang. They reached parity of HHVM/Hacklang with C++. They no longer convert and Facebook runs on HHVM and Hacklang.

Really, who needs Phalcon?