Re: Removing more vacuumlazy.c special cases, relfrozenxid optimizations

Hi,

On 2022-04-01 10:54:14 -0700, Peter Geoghegan wrote:
> On Thu, Mar 31, 2022 at 11:19 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> > The assert is "Assert(diff > 0)", and not "Assert(diff >= 0)".
>
> Attached is v15. I plan to commit the first two patches (the most
> substantial two patches by far) in the next couple of days, barring
> objections.

Just saw that you committed: Wee! I think this will be a substantial
improvement for our users.

While I was writing the above I, again, realized that it'd be awfully nice to
have some accumulated stats about (auto-)vacuum's effectiveness. For us to get
feedback about improvements more easily and for users to know what aspects
they need to tune.

Knowing how many times a table was vacuumed doesn't really tell that much, and
requiring to enable log_autovacuum_min_duration and then aggregating those
results is pretty painful (and version dependent).

If we just collected something like:
- number of heap passes
- time spent heap vacuuming
- number of index scans
- time spent index vacuuming
- time spent delaying
- percentage of non-yet-removable vs removable tuples

it'd start to be a heck of a lot easier to judge how well autovacuum is
coping.

If we tracked the related pieces above in the index stats (or perhaps
additionally there), it'd also make it easier to judge the cost of different
indexes.

- Andres