Re: Add contrib/pg_logicalsnapinspect

On Wed, Oct 9, 2024 at 8:32 PM Bertrand Drouvot
<bertranddrouvot.pg@gmail.com> wrote:
>
> Hi,
>
> On Wed, Oct 09, 2024 at 10:21:31AM -0700, Masahiko Sawada wrote:
> > On Wed, Oct 9, 2024 at 1:12 AM Bertrand Drouvot
> > <bertranddrouvot.pg@gmail.com> wrote:
> > > One option could be (did not test it) to add this switch in construct_array_builtin():
> > >
> > > +               case XIDOID:
> > > +                       elmlen = sizeof(TransactionId);
> > > +                       elmbyval = true;
> > > +                       elmalign = TYPALIGN_INT;
> > > +                       break;
> > >
> > > I think that could make sense and would probably need a dedicated patch for that,
> > > thoughts?
> >
> > Or can we use construct_array() instead?
>
> I had a closer look to d746021de1 (which introduced construct_array_builtin())
> and the hackers thread that lead to it [1].
>
> IIUC, the idea was to:
>
> 1. centralize the hardcoded knowledge that were in the calls to construct_array()
> and deconstruct_array() for built-in types
> 2. notational simplification and bug-proofing
>
> As XIDOID is a built-in type, I think that it would make sense to add it in
> deconstruct_array_builtin()/construct_array_builtin().
>
> I think the reason XIDOID has not been added in d746021de1 is that there were no
> use case at that time (means no existing calls to construct_array()/deconstruct_array()
> with hardcoded XIDOID related arguments).
>
> One could say that we would just add 2 calls to construct_array() in the pg_logicalinspect
> module but, for example, d746021de1 also took care of CSTRINGOID that had a single
> call at that time:
>
> $ git show d746021de1 | grep deconstruct_array_builtin | grep -c CSTRINGOID
> 1
> $ git show d746021de1 | grep construct_array_builtin | grep -v deconstruct_array_builtin | grep -c CSTRINGOID
> 1
>
> So I think that having construct_array_builtin()/deconstruct_array_builtin()
> taking care of XIDOID is the way to go. If that makes sense to you then I'll
> submit a dedicated patch for it, thoughts?

Your explanation makes sense to me. I think it can be included in the
main pg_logicalinspect patch as this change is a part of it.

Regards,

--
Masahiko Sawada
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