Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com> writes:
> Why does VACUUM FULL cause the size of this table with a single
> dropped column (1 out of 1000) cause the table size to double?
VACUUM FULL will rewrite the tuples with a null bitmap where they
had none before (cf reform_and_rewrite_tuple). That's only a rather
marginal increase in the tuple size, but in this particular example,
it pushes the tuples from just under half a page to just over, so
that you go from 2 tuples/page to 1.
regards, tom lane