Re: VACUUM output

Dmitry Tkach <dmitry(at)openratings(dot)com> writes:
> I was wonderring if someone could please explain to me how to read the
> output of a VACUUM command?
> ...
> What is the meaning of these statistics? Partciularly, "Vac", "Removed"
> and "UnUsed"?

I believe "Vac" and "Removed" are the same thing, viz the number of dead
tuples removed in the current VACUUM cycle. They're measured in
different places though, so I'd not care to swear on a stack of bibles
that they could never be different. "UnUsed" is the number of unused
tuple pointers (line pointers) present in the table, ie, line pointers
that used to point to tuples that've been recycled. At 4 bytes apiece
you don't need to panic about those; they'll get reused eventually,
and even if they don't they're not costing much.

regards, tom lane