Re: Report bytes and transactions actually sent downtream

On Wed, Sep 24, 2025 at 6:43 PM Bertrand Drouvot

<bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
>
> Hi,
>
> On Wed, Sep 24, 2025 at 03:37:07PM +0530, Ashutosh Bapat wrote:
> > On Wed, Sep 24, 2025 at 1:55 PM Bertrand Drouvot
> > <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> > > Right. But, in the example above, do you consider "skip-empty-xacts" as "core"
> > > or "plugin" filtering?
> > >
> > > It's an option part of the "test_decoding" plugin, so it's the plugin choice to
> > > not display empty xacts (should the option be set accordingly). Then should it
> > > be reported in plugin_filtered_bytes? (one could write a plugin, decide to
> > > skip/filter empty xacts or whatever in the plugin callbacks: should that be
> > > reported as plugin_filtered_bytes?)
> >
> > If a transaction becomes empty because the plugin filtered all the
> > changes then plugin_filtered_bytes will be incremented by the amount
> > of filtered changes. If the transaction was empty because core didn't
> > send any of the changes to the output plugin, there was nothing
> > filtered by the output plugin so plugin_filtered_bytes will not be
> > affected.
> >
> > skip_empty_xacts controls whether BEGIN and COMMIT are sent for an
> > empty transaction or not. It does not filter "changes". It affects
> > "sent_bytes".
>
> skip_empty_xacts was just an example. I mean a plugin could decide to filter all
> the inserts for example (not saying it makes sense). But I think we'are saying the
> same: say a plugin wants to filter the inserts then it's its responsability to
> increment ctx->stats->filteredBytes in its "change_cb" callback for the
> REORDER_BUFFER_CHANGE_INSERT action, right?

Right.

> If so, I wonder if it would make
> sense to provide an example in the test_decoding plugin (I can see it's done
> for pgoutput but that might sound more natural to look in contrib if one is
> searching for an example).

test_decoding does not make use of publication at all. Publication
controls filtering and so test_decoding does not have any examples of
filtering code. Doesn't make sense to add code to manipulate
filteredBytes there.

--
Best Wishes,
Ashutosh Bapat