How to load database from disc to in-memory for ORACLE 12c

I am new to oracle 12c and trying to measure the query time for the two cases,

Disc based database
In-memory database

How can I know that the database I am currently accessing is on disc or in in-memory? How to enable the in-memory option so that I can load the data into memory?

Solution

1) Check the value of the initialization parameter inmemory_size.

SQL>show parameter inmemory_size

2) Set the value of inmemory_size.

SQL>ALTER SYSTEM SET inmemory_size = 20G scope=spfile;

You may need to increate SGA size as well since IM column store takes memory from it.

3) Alter table to load into memory

SQL>ALTER TABLE hr.emp INMEMORY;