[BeginnerQuestion]Why these is 6 rows in my SELECT statement?

2022年9月8日(木) 17:37 BeginnerC <chuxuec@outlook.com>:

Hello community,
I am checking my pg_stat_activity view,but something confused me.
Just like this:

postgres=# SELECT wait_event_type, wait_event FROM pg_stat_activity;
wait_event_type | wait_event
-----------------+---------------------
Activity | AutoVacuumMain
Activity | LogicalLauncherMain
|
Activity | BgWriterHibernate
Activity | CheckpointerMain
Activity | WalWriterMain
(6 rows)

As you can see, the third row is empty,but I don't know why.
Can anyone provide some solution to me?

It's empty because that's your own client session and it's not waiting
on anything :).

postgres=# SELECT pg_backend_pid();
pg_backend_pid
----------------
24941
(1 row)

postgres=# SELECT pid, backend_type, wait_event_type, wait_event
FROM pg_stat_activity;
pid | backend_type | wait_event_type |
wait_event
-------+------------------------------+-----------------+---------------------
20859 | autovacuum launcher | Activity | AutoVacuumMain
20860 | logical replication launcher | Activity |
LogicalLauncherMain
21554 | walsender | Activity | WalSenderMain
24941 | client backend | |
20856 | background writer | Activity | BgWriterHibernate
20855 | checkpointer | Activity | CheckpointerMain
20858 | walwriter | Activity | WalWriterMain
(7 rows)

Regards

Ian Barwick

On Thu, Sep 08, 2022 at 04:37:00PM +0800, BeginnerC wrote:

Hello community,
I am checking my pg_stat_activity view,but something confused me.
Just like this:

postgres=# SELECT wait_event_type, wait_event FROM pg_stat_activity;
wait_event_type | wait_event
-----------------+---------------------
Activity | AutoVacuumMain
Activity | LogicalLauncherMain
|
Activity | BgWriterHibernate
Activity | CheckpointerMain
Activity | WalWriterMain
(6 rows)

As you can see, the third row is empty,but I don't know why.
Can anyone provide some solution to me?
Thanks in advance!

Please do:

\pset null '-- null --'
SELECT wait_event_type, wait_event FROM pg_stat_activity;

it will most likely show -- null -- in these fields. which means values
in these columns are null.SELECT wait_event_type, wait_event FROM
pg_stat_activity;

You can find more about this/these backends by doing:

select * from pg_stat_activity where wait_event_type is null \gx

depesz