postgres_fdw: from where, is the resource utilized? remote or local?

I have an OLTP database and ETL jobs are running in the same database in the background. I was thinking of separating the OLTP and ETL instances so that resource utilization would be distributed. Basically, the OLTP instance should have fewer or no ETL overhead. The idea is to create foreign tables on the ETL instance connecting to OLTP remote server using *postgres_fdw*. I understand that Postgres will fetch chunks of data from the remote server using the cursor. Can someone please help me if my understanding is right that running a complex query including foreign tables would use resources(RAM,CPU) from the local server? and is the remote server safe from these executions overhead? And if I am wrong which instance resources would Postgres use to run a complex SQL with joins on foreign tables? Thanks in advance!