VACUUM does not return disk space to the OS, instead it marks dead rows to be reused for future writes. My server has almost ran out of disk space, afterwards I ran
DELETE FROM big_table to clear about 30% of rows, followed by a manual
No space was given back to the OS, which is fine. How many rows can I still insert before running out of space?
df -h is a useless metric for obvious reasons. Is there a query to see postgres' used disk space vs available to postgres' disk space?