I’m looking for some advice on how to determine the DB size on disk to trigger some cleanup tasks (deleting old data) if some threshold is reached.
Let’s say that for simplicity I don’t want to ask for the size on disk to the OS, but rather to PostgreSQL itself. And I only have a single database other than the defaults (‘template’, etc).
In that scenario is using pg_database_size() reasonable? Does that function return the actual size on disk or is it a calculation? Is there a better alternative?
Yes, pg_database_size() gives the size from disk level. IIRC, it do "du -h <DB oid folder>" kind of method.