Table placed only in RAM, visibility for all
Daniel Caldeweyher commented
Just create a tablespace on /dev/shm with a low page cost
Darren Duncan commented
It should be possible to do this both with private table variables and public/shared ones. On the other hand, if Postgres provides the ability to selectively say that some tables are not logged and otherwise hint that they are small or should be kept in RAM where possible, that should meet the goal, perhaps.
In-memory tables - good way to improve perfomance.