Re: Vacuum full connection exhaustion

> On Aug 7, 2024, at 10:34, Costa Alexoglou  wrote:
> 
> Hey folks,
> 
> I noticed something weird, and not sure if this is the expected behaviour or not in PostgreSQL.
> 
> So I am running Benchbase (a benchmark framework) with 50 terminals (50 concurrent connections).
> There are 2-3 additional connections, one for a postgres-exporter container for example.
> 
> So far so good, and with a `max_connections` at 100 there is no problem. What happens is that if I execute manually `VACUUM FULL` the connections are exhausted.

VACUUM FULL takes an exclusive lock on the table that it is operating on.  It's possible that a connection becomes blocked on that exclusive lock waiting for the VACUUM FULL to finish, the application sees the connection stopped and fires up another one (this is common in container-based applications), that one blocks... until all of the connections are full of queries waiting on that VACUUM FULL.