I haven't tried PostgreSQL as an in-memory solution, but in my another benchmark it has reached a good performance in comparison with other on-disk solutions. Thank you! I've scheduled benchmark of PostgreSQL in RAM.

Do you mean using postgres tablespaces backed by memory or do you mean using a FDW?

If you do mean using a ramdisk tablespace, the postgres docs recommend not doing that. However, if you really want to do that, make sure you attach xlog (the WAL table) to that ramdisk tablespace as well, otherwise every transaction will still hit the disk.

Not the poster upthread. But if you have enough memory (shared_buffers) and use unlogged tables, the effect is going to be that both reads and writes pretty much only hit memory, no disk. Without going through the trouble of moving tablespaces or anything.

Putting tables in RAM and setting the config as you suggest works just fine.