On Fri, Jan 15, 2016 at 11:16 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I believe that there would be ramifications for some of the index AMs
> too. For example, if left to its own devices GIN would consider VACUUM
> to include flushing its pending-list pages, which more than likely will
> increase not reduce the total index size. I'm not sure that it has
> any ability to omit that step; can it remove dead entries directly off
> the pending pages, or only from the main index?
It cannot vacuum the pending list directly. That is why it is a bug
for the vacuum to short-cut out of the pending list cleanup step when
it finds someone else already cleaning it. For correctness it has to
either clean it itself, or wait until the other process is done (or at
least, done up to the point where the tail was at the time the vacuum
started).
Cheers,
Jeff