Re: New vacuum option to do only freezing

I wrote:
> I'm thinking that we really need to upgrade vacuum's reporting totals
> so that it accounts in some more-honest way for pre-existing dead
> line pointers.  The patch as it stands has made the reporting even more
> confusing, rather than less so.

Here's a couple of ideas about that:

1. Ignore heap_page_prune's activity altogether, on the grounds that
it's just random chance that any cleanup done there was done during
VACUUM and not some preceding DML operation.  Make tups_vacuumed
be the count of dead line pointers removed.  The advantage of this
way is that tups_vacuumed would become independent of previous
non-VACUUM pruning activity, as well as preceding index-cleanup-disabled
VACUUMs.  But maybe it's hiding too much information.

2. Have heap_page_prune count, and add to tups_vacuumed, only HOT
tuples that it deleted entirely.  The action of replacing a DEAD
root tuple with a dead line pointer doesn't count for anything.
Then also add the count of dead line pointers removed to tups_vacuumed.

Approach #2 is closer to the way we've defined tups_vacuumed up to
now, but I think it'd be more realistic in cases where previous
pruning or index-cleanup-disabled vacuums have left lots of dead
line pointers.

I'm not especially wedded to either of these --- any other ideas?

            regards, tom lane