pgxpool: different MaxConnLifetime for fallback hosts about pgx HOT 1 OPEN

I'm not sure that baking custom fallback handling directly into pgx/pgxpool is a good idea. However, I would be more open to adding features that make it more convenient for the applications to implement exactly the behavior they want.

I think AfterRelease (and possibly AfterConnect) actually is the right approach. One newer feature that could help with this is https://pkg.go.dev/github.com/jackc/pgx/[email protected]/pgconn#PgConn.CustomData. With that you can associate arbitrary values with a connection. I would expect it to be less than 10 lines of code overall to have an AfterConnect that stored the current time in CustomData and a AfterRelease that checked the age.

Beyond that, one thing I've thought of is each layer above *pgconn.PgConn storing a reference to itself in CustomData. That is, a *pgconn.PgConn would have a reference to the *pgx.Conn and the *pgxpool.Conn. I haven't implemented it yet, there are few subtleties regarding what should happen when a connection is Hijacked.

Possible, some of the internal statistics for a pgxpool.Conn could be made public as well.

from pgx.