More aggressive vacuuming of unlogged relations?

Hi,

The patch in [1] makes the horizon logic in procarray.c aware of temp
tables not needing to care about other session's snapshots (also
discussed in[2]). Extending a7212be8b9e, which did that for VACUUM, but
not HOT pruning etc.

While polishing that patch I was wondering whether there are other
classes of relations that we might want to treat differently. And
there's one more that we don't special case right now: unlogged tables.

As unlogged tables aren't replicated via physical rep, we don't need to
apply vacuum_defer_cleanup_age, hot standby feedback and slot based
horizons.

The obvious question is, is that worth doing? My intuition is that yes,
it probably is: Unlogged tables are often used for hotly updated
transient state, allowing that to be cleaned up more aggressively will
reduce bloat.

Comments?

Greetings,

Andres Freund

[1] https://www.postgresql.org/message-id/20201015083735.derdzysdtqdvxshp%40alap3.anarazel.de
[2] https://www.postgresql.org/message-id/20201014203103.72oke6hqywcyhx7s%40alap3.anarazel.de