Isolating Session Data between Applications

I think the docs explain it pretty well. It will prefix the uniqueId to each session much like cache-keys prefix keys.

If you are using the files session adapter you can use

$      php -r 'echo session_save_path(), "\n";'

and use

$ less

with one of the file paths to look at the contents of the session and examine what phalcon does with the uniqueId