Re: Fix pg_stat_get_backend_wait_event() for aux processes

At Tue, 3 Feb 2026 12:47:34 +0800, Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com> wrote in
> I reviewed and tested the patch, it works well, and the code change
> looks solid to me.

It seems to have sufficient reliability.

> I only have one small comment. In the following case:
> ```
> if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
> wait_event_type = "<backend information not available>";
> ```
>
> With this patch, aux processes are now supported as well. Do we want to =
> update this message?
>
> For example, in my test system max_connections =3D 100, so procNumber >=3D=
> 100 corresponds to aux processes. If I run:
> ```
> evantest=3D# select pg_stat_get_backend_wait_event(188);
> pg_stat_get_backend_wait_event
> -------------------------------------
> <backend information not available>
> (1 row)
> ```
>
> Here 188 refers to an aux process, but the message still says
> "backend information", which feels a bit misleading. Would it make
> sense to change this to something like "process information not
> available"

pg_stat_get_backend_idset() is documented as returning backend IDs, and
even its name suggests that it deals specifically with backends, but
the returned set also includes aux processes. The glossary, however,
defines a backend as:

> Backend (process)
> Process of an instance which acts on behalf of a client session and
> handles its requests.

This makes the scope of the term "backend" a bit unclear in this
context.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center