Log notice that checkpoint is to be written on shutdown

Hi,

we have seen repeatedly that users can be confused about why PostgreSQL
is not shutting down even though they requested it. Usually, this is
because `log_checkpoints' is not enabled and the final checkpoint is
being written, delaying shutdown. As no message besides "shutting down"
is written to the server log in this case, we even had users believing
the server was hanging and pondering killing it manually.

In order to alert those users that a checkpoint is being written, I
propose to add a log message "waiting for checkpoint ..." on shutdown,
even if log_checkpoints is disabled, as this particular checkpoint might
be important information.

I've attached a trivial patch for this, should it be added to the next
commitfest?

Cheers,

Michael

--
Michael Banck
Projektleiter / Berater
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