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  1. Add backendType to PGPROC, replacing isRegularBackend

  1. Add backendType to PGPROC, replacing isRegularBackend

    Heikki Linnakangas <hlinnaka@iki.fi> — 2026-02-03T20:55:20Z

    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?

[1] 
https://www.postgresql.org/message-id/ujenaa2uabzfkwxwmfifawzdozh3ljr7geozlhftsuosgm7n7q%40g3utqqyyosb6

- Heikki

  2. Re: Add backendType to PGPROC, replacing isRegularBackend

    Nathan Bossart <nathandbossart@gmail.com> — 2026-02-03T21:04:41Z

    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.

-- 
nathan

  3. Re: Add backendType to PGPROC, replacing isRegularBackend

    Bertrand Drouvot <bertranddrouvot.pg@gmail.com> — 2026-02-04T07:17:47Z

    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

  4. Re: Add backendType to PGPROC, replacing isRegularBackend

    Chao Li <li.evan.chao@gmail.com> — 2026-02-04T08:23:16Z

    
> On Feb 4, 2026, at 15:17, Bertrand Drouvot <bertranddrouvot.pg@gmail.com> wrote:
> 
> 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

Yeah, I think we should assign MyBackendType to MyProc->backendType.

InitAuxiliaryProcess() is only called by AuxiliaryProcessMainCommon(), and AuxiliaryProcessMainCommon() is always called after setting MyBackendType, for example:
```
void
BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
{
	sigjmp_buf	local_sigjmp_buf;
	MemoryContext bgwriter_context;
	bool		prev_hibernate;
	WritebackContext wb_context;

	Assert(startup_data_len == 0);

	MyBackendType = B_BG_WRITER;
	AuxiliaryProcessMainCommon();
```

Otherwise, the patch looks good to me. I applied the patch locally, both build and “make check” passed.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/

  5. Re: Add backendType to PGPROC, replacing isRegularBackend

    Heikki Linnakangas <hlinnaka@iki.fi> — 2026-02-04T11:08:45Z

    On 03/02/2026 23:04, 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.

Ok.

>> @@ -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.

Right, that was just a silly mistake.

Fixed that and pushed, thanks!

- Heikki