Re: Subject: bool / vacuum full bug followup

Tom Lane wrote:
> Jeffrey Baker <jwbaker@acm.org> writes:
> > Well, if the table has an associated TOAST table, it is possible
> > that it will suddenly start growing out of control, and nothing you
> > can do with VACUUM will help.  The TOAST system has a free space map
> > (FSM) with some default number of pages it can track.  If you exceed
> > this number, it will become completely unable to reclaim space.
>
> That's a gross misstatement.
>
> If you have more pages with free space than the FSM can track, it will
> forget about the ones with the least free space (at least until the next
> vacuum tries to reload the info).  This will very possibly lead to table
> growth over time, but it's hardly the same as "completely unable to
> reclaim space".
>
> BTW, TOAST has nothing to do with this.  Space in main tables and
> toast tables is tracked alike.

One subtle point is that TOAST space and HEAP space used by a table are
not shared, meaning if you have TOAST space free, that can't be used for
HEAP storage, and via versa.  Of course, a FULL vacuum frees all unused
space.

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