Re: logical decoding and replication of sequences, take 2

On Wed, Feb 21, 2024 at 2:52 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Wed, Feb 21, 2024 at 2:43 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > So the problem is that we might consider the transaction change as
> > non-transaction and mark this flag as true.
>
> But it's not "might" right? It's absolutely 100% certain that we will
> consider that transaction's changes as non-transactional ... because
> when we're in fast-forward mode, the table of new relfilenodes is not
> built, and so whenever we check whether any transaction made a new
> relfilenode for this sequence, the answer will be no.
>
> > But what would have
> > happened if we would have identified it correctly as transactional?
> > In such cases, we wouldn't have set this flag here but then we would
> > have set this while processing the DecodeAbort/DecodeCommit, so the
> > net effect would be the same no? You may question what if the
> > Abort/Commit WAL never appears in the WAL, but this flag is
> > specifically for the upgrade case, and in that case we have to do a
> > clean shutdown so may not be an issue. But in the future, if we try
> > to use 'ctx->processing_required' for something else where the clean
> > shutdown is not guaranteed then this flag can be set incorrectly.
> >
> > I am not arguing that this is a perfect design but I am just making a
> > point about why it would work.
>
> Even if this argument is correct (and I don't know if it is), the code
> and comments need some updating. We should not be testing a flag that
> is guaranteed false with comments that make it sound like the value of
> the flag is trustworthy when it isn't.

+1

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com