docs(databases): Add section about troubleshooting backups

docs/maintain/databases.rst

@@ -1,8 +1,8 @@
 Maintain PostgreSQL
 ===================
 
-Troubleshoot
-------------
+Troubleshoot performance
+------------------------
 
 Check the log file – for example, ``/var/log/postgresql/postgresql-15-main.log`` – if debugging an unscheduled restart of the ``postgres`` service, for example.
 
@@ -102,6 +102,30 @@ To get the table related to a TOAST table, take the number after ``pg_toast_``,
 
    SELECT '16712'::regclass;
 
+Troubleshoot backups
+--------------------
+
+If ``cron`` sends an email like:
+
+.. code-block:: none
+
+   ERROR: [082]: WAL segment 00000001000009FD0000000D was not archived before the 60000ms timeout
+          HINT: check the archive_command to ensure that all options are correct (especially --stanza).
+          HINT: check the PostgreSQL server log for errors.
+          HINT: run the 'start' command if the stanza was previously stopped.
+
+(The same message will appear in a log file like ``/var/log/pgbackrest/STANZA-backup.log``.)
+
+This error occurs occasionally (for example, due to a network issue), and is not a concern. To confirm, after 24 hours, view recent backups with:
+
+.. code-block:: bash
+
+   sudo -u postgres pgbackrest info --stanza=kingfisher-2023
+
+You should see a "full backup" within one week of the error, an "incr backup" the day before the error, and another the day after. (In other words, an incremental backup failed.)
+
+If a full backup failed, re-run the weekly full backup command listed in the ``/etc/cron.d/postgres_backups`` file.
+
 Check usage
 -----------
 

docs/use/databases.rst

@@ -144,7 +144,7 @@ Improve slow queries
 
 .. seealso::
 
-   `PostgreSQL <https://ocp-software-handbook.readthedocs.io/en/latest/services/postgresql.html>`__ in the Software Development Handbook
+   *Define tables*, *Define indexes* and *Paginate rows* under `PostgreSQL <https://ocp-software-handbook.readthedocs.io/en/latest/services/postgresql.html>`__ in the Software Development Handbook
 
 To see the queries running under your user account, run: