> To put it simply, VACUUM has no problems with connections being open. What you're thinking of here are locks, and locks only occur once you're in a transactio

> To put it simply, VACUUM has no problems with connections being open. What you're thinking of here are locks, and locks only occur once you're in a transaction and have accessed some table rows, which are now subject to various isolation rules. I think you are correct except about this. What he is thinking about is indeed as he said transactions. Locks in PostgreSQL do also interfere with VACUUM but that is seldom the problem in practice since locks are usually taken at the row level and reading rows does not require any row locks. Open transactions are the main culprit when it comes to vacuum problems and it does not matter much if they have taken locks or not.