As a unicorn/thin user, could someone briefly explain what the differences are in this release that might convince me to give Passenger a shot? The out-of-band improvements are already there in Unicorn.
As explained in the article, our Out-of-Band Work mechanism is more general and more flexible. The most important points are:
- Unicorn's mechanism is limited to garbage collection. Phusion Passenger's allows any arbitrary work.
- Unicorn's doesn't work well with multithreaded apps, Phusion Passenger's does.
- Unicorn's doesn't spawn additional workers. In certain situations it can happen that all workers are busy garbage collecting. When Phusion Passenger encounters such a situation, it will spawn an additional worker. Phusion Passenger guarantees that, while performing out-of-band-work, there are at least PassengerMinProcesses processes ready to process any requests.
Phusion Passenger 4 also introduces features not found in Unicorn and Thin:
- Support for multiple Ruby interpreters inside the same instance. But to be fair Unicorn and Thin are designed to be run in a different way so this may or may not be an advantage for you.
- JRuby support.
- Python support, and in the future more languages.
- Real-time disk-backed response buffering, first introduced in 4.0 beta 1. Unicorn relies on web server buffering which tends to buffer the entire response before sending it to the client. Phusion Passenger 4 allows you to use Rails 4 streaming with ease, without blocking the server on slow clients, with good performance and without configuration.