Hi!
This will vary according to the dimension length of your vectors.
Here we have an example for this calculation
Assuming your vectors has 1536 dimensions, this is the calculation you need to do, for storing 1 million objects:
2 * 1e6 * (1536 * 4)
As a rule of thumb, we always double the required memory (this is the 2x)
so you are looking to something around 12G of ram. This is not counting the maxconnections.
Let me know if this helps.