Question on adl_next_worker condition in autovacuum launcher

Hi,

With regard to my previous post [1], I have a question about the
autovacuum launcher codes.

In do_start_worker(), the following conditions determins whether a database
should be skipped or not.

                /*
                 * Skip this database if its next_worker value falls between
                 * the current time and the current time plus naptime.
                 */
                if (!TimestampDifferenceExceeds(dbp->adl_next_worker,
                                                current_time, 0) &&
                    !TimestampDifferenceExceeds(current_time,
                                                dbp->adl_next_worker,
                                                autovacuum_naptime * 1000))
                    skipit = true;

This means a database is skipped when 
 current_time  < adl_next_woker < current_time + autovacuum_naptime.

However, I don't quite understand why ther upper bound condition is necessary.
After a database has been processed, adl_next_woker is set in launch_worker() as follows:

                /*
                 * add autovacuum_naptime seconds to the current time, and use
                 * that as the new "next_worker" field for this database.
                 */
                avdb->adl_next_worker =
                    TimestampTzPlusMilliseconds(now, autovacuum_naptime * 1000);

Here "now < current_time (in do_start_worker())", so I believe
 "adl_next_woker < current_time + autovacuum_naptime"
will always be true. Therefore, it seems redundant to explicitly check the upper bound.

Am I missing something? I’d appreciate it if anyone could clarify this for me.

[1] https://www.postgresql.org/message-id/20250802002027.cd35c481f6c6bae7ca2a3e26%40sraoss.co.jp

Regards,
Yugo Nagata
-- 
Yugo Nagata <nagata@sraoss.co.jp>