Re: logical streaming of xacts via test_decoding is broken

On Wed, Nov 11, 2020 at 7:05 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Wed, Nov 11, 2020 at 6:59 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Wed, Nov 11, 2020 at 10:00 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > >
> > > On Tue, Nov 10, 2020 at 7:20 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > >
> > > > On Tue, Nov 10, 2020 at 2:25 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > > > >
> > > >
> > > > You can probably add a comment as to why we are disallowing this case.
> > > > I thought of considering 'stream-changes' parameter here because it
> > > > won't make sense to give this parameter without it, however, it seems
> > > > that is not necessary but maybe adding a comment
> > > > here in that regard would be a good idea.
> > >
> > > Should we also consider the case that if the user just passed
> > > skip_empty_streams to true then we should automatically set
> > > skip_empty_xacts to true?
> > >
> >
> > Is there any problem if we don't do this? Actually, adding
> > dependencies on parameters is confusing so I want to avoid that unless
> > it is really required.
> >
> > > And we will allow the 'skip_empty_streams' parameter only if
> > > stream-changes' is true.
>
> The reason behind this thought is that if the user doesn't pass any
> value for 'skip_empty_xacts' then the default value will be false and
> if the user only pass 'skip_empty_streams' to true then we will error
> out assuming that skip_empty_xacts is false but skip_empty_streams is
> true. So it seems instead of error out we can assume that
> skip_empty_streams true mean skip_empty_xacts is also true if nothing
> is passed for that.
>

So, let's see the overall picture here. We can have four options:
skip_empty_xacts = true, skip_empty_stream = false;
skip_empty_xacts = true, skip_empty_stream = true;
skip_empty_xacts = false, skip_empty_stream = false;
skip_empty_xacts = false, skip_empty_stream = true;

I think we want to say the first three could be supported and for the
last one either we can either give an error or make its behavior
similar to option-2? Is this what your understanding as well?

Another thing I am thinking let's just not expose skip_empty_stream to
the user and consider the behavior based on the value of
skip_empty_xacts. Internally, in the code, we can still have different
variables to distinguish between empty_xacts and empty_streams.

--
With Regards,
Amit Kapila.