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Thread: pg_settings.unit and DefineCustomXXXVariable

pg_settings.unit and DefineCustomXXXVariable

From
Luca Ferrari
Date:
Hi all,
I need to define a few GUCs, and for that purpose I'm using
DefineCustomXXXVariable functions that provide hooks for assignment,
show and check. However it is not clear to me if it is possible to
populate the unit column in pg_settings for the custom defined
variables, and if so, how.
Any suggestion is appreciated.

Thanks,
Luca

Re: pg_settings.unit and DefineCustomXXXVariable

From
Matthias van de Meent
Date:
On Wed, 8 Jan 2025 at 11:13, Luca Ferrari <fluca1978@gmail.com> wrote:
>
> Hi all,
> I need to define a few GUCs, and for that purpose I'm using
> DefineCustomXXXVariable functions that provide hooks for assignment,
> show and check. However it is not clear to me if it is possible to
> populate the unit column in pg_settings for the custom defined
> variables, and if so, how.

DefineCustomXXXVariable has a 'flags' argument, into which GUC_UNIT_*
can be or-ed.
AFAIK, the options provided in guc.h are the only kinds of units
supported and available, and I think only integer variables actually
support the unit conversion implied by the unit options.

Kind regards,

Matthias van de Meent

Re: pg_settings.unit and DefineCustomXXXVariable

From
Tom Lane
Date:
Matthias van de Meent <boekewurm+postgres@gmail.com> writes:
> On Wed, 8 Jan 2025 at 11:13, Luca Ferrari <fluca1978@gmail.com> wrote:
>> I need to define a few GUCs, and for that purpose I'm using
>> DefineCustomXXXVariable functions that provide hooks for assignment,
>> show and check. However it is not clear to me if it is possible to
>> populate the unit column in pg_settings for the custom defined
>> variables, and if so, how.

> DefineCustomXXXVariable has a 'flags' argument, into which GUC_UNIT_*
> can be or-ed.

Correct.  contrib/auto_explain has some examples.

> AFAIK, the options provided in guc.h are the only kinds of units
> supported and available, and I think only integer variables actually
> support the unit conversion implied by the unit options.

Nowadays we allow units for float GUCs as well.  (Originally it was
indeed just for integers.  But at some point we decided an existing
integer value with units needed to become float, and then we had
to back-fill the implementation for compatibility's sake.)

            regards, tom lane

Re: pg_settings.unit and DefineCustomXXXVariable

From
Luca Ferrari
Date:
On Wed, Jan 8, 2025 at 4:18 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Matthias van de Meent <boekewurm+postgres@gmail.com> writes:

> > DefineCustomXXXVariable has a 'flags' argument, into which GUC_UNIT_*
> > can be or-ed.

Thanks Matthias and Tom for the explaination.
Since I'm needing to define "seconds", GUC_UNIT_S is what I was looking for.


Luca