There is "Don’t use any blocking I/O functions in Aerys." warning at https://amphp.org/aerys/io#blocking-io. Should I use PPM instead of Aerys if I need usage of PDO (e.g., Prooph components) and want to reuse initialized application instance for handling different requests?
I'm not bound to any existent PPM adapter (e.g., Symfony). Is there a way to reuse Aerys code (e.g., Router) for request-response logic when using PPM on top of Aerys (https://github.com/php-pm/php-pm/pull/267)?
You can just increase the worker count using the -w switch for the command line script to be higher if you want to use blocking functions. It's definitely not optimal, but with enough workers the blocking shouldn't be too noticeable, except for an increasing latency, which might occur.
Another possibility is to move the blocking calls into one or multiple worker threads with amphp/parallel.
As long as the responses are relatively fast everything should be fine. The issue begins if there's a lot of load and things get slower and might time out, because these are very long blocks then.
PHP-PM doesn't offer too much benefit over using Aerys directly. It redirects requests to a currently free worker, but with high enough load the kernel load balancing will probably good enough and not all requests that take longer will be routed to one worker. In fact, using Aerys will probably be better, because it's production ready and has multiple independent workers instead of one master that might be a bottleneck. PHP-PM could solve that in a better way, but it's currently not implemented. Additionally, Aerys supports keep-alive connections, which PHP-PM does currently not support.