Splitting queries across servers

Hello,

Our postgresql database is getting too big to be handled by one server. We
need the database to be in RAM and cannot afford swapping. At the moment,
we're using only 3GB or RAM, however our business growth is going to drive
this number into the double digits zone, maybe triple digits.

What are our options ?

I am a little bit ignorant in this part of RDBM. Can we distribute our
tables across multiple servers (read server+postgres) and perform
distributed SQL queries ? If so, how does that work ? I am totally
resourceless!

Thank you in advance

Max.