PostgreSQL database buffer cache and OS cache

Unlike many traditional database products, PostgreSQL does not assume or even prefer that the majority of the memory on the system be allocated for its use. Most reads and writes from the database are done using standard operating system calls that allows the operating system's cache to work in its usual fashion ... PostgreSQL database buffer cache and OS cache

Useful SQLs to check contents of PostgreSQL shared_buffer

Want to know the relations buffered in database share buffer? the relations usage count in PostgreSQL shared buffer? and top relation in cache?... Useful SQLs to check contents of PostgreSQL shared_buffer

I used to be a DBA for a Bank, In  charge of backend server and database maintenance for 5 years. now I'm not DBA, but never away from database, I still use it everyday. Mainly using PostgreSQL 9(~70GB), MySQL 5.4(5GB) and different version of BerkeleyDB I'm using in my script the size range from few kb to GB.