vacuum visibility relevance

Hi All,

Simplified Scenario:
40+ gig table with 20+ indexes receiving log event type records in an append only fashion.
One of the columns is a sequence ID.
PG version 11.4

If I start a vacuum on this table when sequence ID is 1 million, and the table continues to accumulate new events, when vacuum completes, should I be thinking about the state of the table and indexes as being vacuumed up to 1 million? Or is vacuum also operating on records inserted after vacuum started?

Is there any reason to think about this differently when the vacuum is manual as opposed to auto?

I attempted to deal with the append only issue corrected in PG13 by setting autovacuum_freeze_max_age low enough to trigger vacuum but that has been such a wild card I abandoned it. I'm now trying to find a formula to trigger a manual vacuum. There are stats gathering processes pulling from the most recently added data all the time so my priority is to keep performance high for those. Secondly, there's a ton of memory allotted so running vacuum freeze before table pages age out of memory seems like a good idea.

I am having trouble with autovacuum keeping up and I suspect there's a communication problem with the stats collector but have put off looking into that because updating to PG15 was "right around the corner". Meanwhile, I have had to run multiple-thread scripts to keep up vacuum. Manual vacuums always work and updates stats correctly but autovacuums hang and occupies workers doing nothing.

I realize these are 2 completely different issues. I would love to have better understanding of the initial question but it feels like I may not have to be very aware of how that works if I knew what was causing the latter issue. Any hints, pointers and references are always appreciated.

- ​Senor