Re: A question about pages. Still not clear

tmorelli@tmorelli.com.br writes:
> Every insert was like this:
> insert into t values (repeat('a',8000));
> Obviously, there must be some kind of compression (the toast table is empty!).

Sure, that's highly compressible data ;-).  I repeated your experiment
and then did VACUUM FULL VERBOSE, which provided me this information:

    Nonremovable row versions range from 135 to 135 bytes long.

So 8000 'a's compress down into about a hundred bytes, plus the row
header overhead.  (Your mileage may vary a bit depending on machine
architecture, PG version, etc.)

> Is there any way of knowing exactly WHEN there will be a new page allocation?

No.  Why should you care?

            regards, tom lane