[sqlite] In-Memory estimate size

[Michele Pradella]

Which is the best way to estimate the size of an In-Memory DB?
Now I'm using (PRAGMA page_size)*(PRAGMA page_count) to have an idea of 
the size in RAM of the db. It's quite ok but obviously it gives a value 
less than the real (probably because indexes and other stuff are missing 
from cont)
For example a DB that is about 5GB of ram with the operation above can 
result in 4GB