Change log level for notifying hot standby is waiting non-overflowed snapshot

Hi,

When a hot standby is restarted in a state where subtransactions have
overflowed, it may become inaccessible:

$ psql: error: connection to server at "localhost" (::1), port 5433
failed: FATAL: the database system is not yet accepting connections
DETAIL: Consistent recovery state has not been yet reached.

However, the log message that indicates the cause of this issue seems to
be only output at the DEBUG1 level:

elog(DEBUG1,
"recovery snapshot waiting for non-overflowed snapshot or "
"until oldest active xid on standby is at least %u (now %u)",
standbySnapshotPendingXmin,
running->oldestRunningXid);

I believe this message would be useful not only for developers but also
for users.
How about changing the log level from DEBUG1 to NOTICE or else?

Background:
One of our customers recently encountered an issue where the hot standby
became inaccessible after a restart.
The issue resolved itself after some time and I suspect it was caused by
a subtransaction overflow.
If the log level had been higher one, it would have been easier to
diagnose the problem.
..Even if it was a NOTICE, it may be difficult to notice the cause if
the log_min_message is set to default WARNING, but well, it seems a
higher log level is better than DEBUG1.

I would appreciate your thoughts.

--
Regards,

--
Atsushi Torikoshi
Seconded from NTT DATA GROUP CORPORATION to SRA OSS K.K.