Description of problem:
It is possible that a situation occurs when a replication slot is not being consumed from. This causes WAL log to accumulate on the database server which will eventually lead to the database filesystem filling up and system failure.

This is something we can monitor from the application and ideally send an alert or notification so the admin can fix the situation.

In more detail, we will want to check that the 'active' column of the pg_replication_slots table is always 'true'. When a slot is not being consumed from, it becomes inactive and this is a precursor to disk usage issues.