As of Go1.17, retry logic and various other logic rely on the exact error value driver.ErrBadConn being returned if the connection is in a bad state. Various calls, such as the IsValid method may be called if supported on a driver that will prevent bad connections from poisoning the pool. However, right now, a driver still has to make a decision to return an interesting error or to get retry logic.

See denisenkom/go-mssqldb#586

I propose that throughout database/sql we use errors.Is rather then a direct comparison to driver.ErrBadConn.