On Thu, Aug 8, 2024 at 10:12 AM Christophe Pettus <xof@thebuild.com> wrote:
> On Aug 7, 2024, at 10:34, Costa Alexoglou <costa@dbtune.com> 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.
"I see a lock, so let's cause another one!" That's crazy.
