Re: Add backendType to PGPROC, replacing isRegularBackend

Hi,

On Tue, Feb 03, 2026 at 03:04:41PM -0600, Nathan Bossart wrote:
> On Tue, Feb 03, 2026 at 10:55:20PM +0200, Heikki Linnakangas wrote:
> > I propose a little refactoring, attached, to replace the "isRegularBackend"
> > field in PGPROC with full "backendType".
> >
> > Andres briefly suggested this a while back [1]:
> >
> > On Fri, 22 Nov 2024 at 22:13, Andres Freund <andres(at)anarazel(dot)de>
> > wrote:
> >> Or we could have a copy of the backend type in PGPROC.
> >
> > but we didn't follow up on that approach. I don't see why, it seems so much
> > simpler than what we ended up doing. Am I missing something?
>
> At a glance, it looks reasonable to me. I don't recall whether I explored
> this approach, but at the very least I'm unaware of any reason it wouldn't
> work.
>
> > @@ -684,7 +684,7 @@ InitAuxiliaryProcess(void)
> > MyProc->databaseId = InvalidOid;
> > MyProc->roleId = InvalidOid;
> > MyProc->tempNamespaceId = InvalidOid;
> > - MyProc->isRegularBackend = false;
> > + MyProc->backendType = B_INVALID;
> > MyProc->delayChkptFlags = 0;
> > MyProc->statusFlags = 0;
> > MyProc->lwWaiting = LW_WS_NOT_WAITING;
>
> Hm. So for auxiliary processes, this would always be unset? That appears
> to be alright for today's use-cases, but it could be a problem down the
> road.

Yeah, and that would contradict what their associated "Main" functions set.

For example, for the checkpointer we now have:

(gdb) p MyProc->backendType
$1 = B_INVALID
(gdb) p MyBackendType
$2 = B_CHECKPOINTER <---- set by CheckpointerMain()

Also one point to notice:

- bool isRegularBackend; /* true if it's a regular backend. */
+ BackendType backendType; /* what kind of process is this? */

we're going from 1 byte to 4 bytes and that does not change the struct size (thanks
to the padding): still 832 bytes. I guess that's good that it is still a multiple
of 64.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com