Re: Add contrib/pg_logicalsnapinspect

Hi,

On Thu, Aug 29, 2024 at 02:51:36PM +0530, Amit Kapila wrote:
> On Wed, Aug 28, 2024 at 1:25 AM Bertrand Drouvot
> <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> >
> > On Mon, Aug 26, 2024 at 07:05:27PM +0530, Amit Kapila wrote:
> > > On Thu, Aug 22, 2024 at 5:56 PM Bertrand Drouvot
> > > <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> > > >
> > > > 2. The SnapBuildOnDisk and SnapBuild structs are now exposed to public. Means
> > > > we should now pay much more attention when changing their contents but I think
> > > > it's worth it.
> > > >
> > >
> > > Is it possible to avoid exposing these structures? Can we expose some
> > > function from snapbuild.c that provides the required information?
> >
> > Yeah, that's an option if we don't want to expose those structs to public.
> >
> > I think we could 1/ create a function that would return a formed HeapTuple, or
> > 2/ we could create multiple functions (about 15) that would return the values
> > we are interested in.
> >
> > I think 2/ is fine as it would give more flexiblity (no need to retrieve a whole
> > tuple if one is interested to only one value).
> >
>
> True, but OTOH, each time we add a new field to these structures, a
> new function has to be exposed. I don't have a strong opinion on this
> but seeing current use cases, it seems okay to expose a single
> function.

Yeah that's fair. And now I'm wondering if we need an extra module. I think
we could "simply" expose 2 new functions in core, thoughts?

> > What do you think? Did you have something else in mind?
> >
>
> On similar lines, we can also provide a function to get the slot's
> on-disk data.

Yeah, having a way to expose the data from the disk makes fully sense to me.

> IIRC, Bharath had previously proposed a tool to achieve
> the same. It is fine if we don't want to add that as part of this
> patch but I mentioned it because by having that we can have a set of
> functions to view logical decoding data.
>

That's right. I think this one would be simply enough to expose one or two
functions in core too (and probably would not need an extra module).

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
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