note about full vacuum

howto/postgresql.md

@@ -264,6 +264,12 @@ One more trick: this will show last VACUUM dates on tables:
 
 Some of the ideas above were found on [this datadog post](https://www.datadoghq.com/blog/postgresql-vacuum-monitoring/).
 
+Finally, note that the Debian 10 ("buster") version of PostgreSQL (11) does
+not support reporting on "FULL" VACUUM, that feature was introduced in
+PostgreSQL 12. Debian 11 ("bullseye") has PostgreSQL 13, but progress
+there is reported in the `pg_stat_progress_cluster` table, so the
+above might not work even there.
+
 ## Pager playbook
 
 TODO: there's some more information about backup handling in the