Re: Blocking queries on a hot standby?

> On Sep 15, 2023, at 12:30 AM, Victor Sudakov <vas(at)sibptus(dot)ru> wrote:
>
> Can you imagine, at least theoretically, any kind of query on a
> physical replica (hot standby) which would block other queries on the
> same replica?

The only thing that comes to mine is advisory locks and also queries can block replication replay.

prod=# select pg_is_in_recovery();
-[ RECORD 1 ]-----+--
pg_is_in_recovery | t

prod=# select * from blocked_session;
-[ RECORD 1 ]---+-----------------------------
pid | 39330
tree | 39330
root | 39330
level | 0
user | rui
state | idle
state_duration | 00:01:01.663597
wait_event_type | Client
wait_event | ClientRead
lockmode | ExclusiveLock
locktype | advisory
granted | t
lock_wait |
blocked | 1
query | select pg_advisory_lock(42);
objects |
-[ RECORD 2 ]---+-----------------------------
pid | 39327
tree | 39330.39327
root | 39330
level | 1
user | rui
state | active
state_duration | 00:00:51.407894
wait_event_type | Lock
wait_event | advisory
lockmode | ExclusiveLock
locktype | advisory
granted | f
lock_wait | 00:00:51.407746
blocked | 0
query | select pg_advisory_lock(42);
objects |