Sorry, the pg_stat_activity sql was executed from a session connecting to a wrong postgresql. It DOES show in the view, and the wait event is SyncRep.
postgres=# select * from pg_stat_activity where application_name='psql' and datname='example';
-[ RECORD 1 ]----+--------------------------------------
....
wait_event_type | IPC
wait_event | SyncRep
state | active
....
We are using sync replication, if a session runs an insert, and then commit, the client is actually waiting for commit to complete, but looks like this wait doesn't show in pg_stat_activity.
In one session I inserted a row (auto commit), it hangs there.
example=# insert into test_timteout select '1';
^CCancel request sent
WARNING: canceling wait for synchronous replication due to user request
DETAIL: The transaction has already committed locally, but might not have been replicated to the standby.
INSERT 0 1
example=# select pg_backend_pid();
pg_backend_pid
----------------
19325
(1 row)
During the hung period.
postgres=# select * from pg_stat_activity where pid=19325;
(0 rows)
postgres=#
If there is no event for such commit, anyway to find out such session which pending on commit(sync replication)