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

[BeginnerC <chuxuec@xxxxxxxxxxx>]

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!

Yours,

BeginnerC.