Re: BUG #16643: PG13 - Logical replication - initial startup never finishes and gets stuck in startup loop

On 2020-Sep-30, Tom Lane wrote:

> Henry Hinze <henry.hinze@gmail.com> writes:
> > I've made an important observation!
> > Since I had the impression this setup was already working with RC1 of PG
> > 13, I re-installed RC1 and did the same test. And it's working fine!
> 
> Ugh.  So that points the finger at commits 07082b08c/bfb12cd2b,
> which are the only nearby change between rc1 and 13.0.  A quick
> comparison of before-and-after checkouts confirms it.

Oh dear.

> After some digging around, I realize that that commit actually
> resulted in a protocol break.  libpqwalreceiver is expecting to
> get an additional CommandComplete message after COPY OUT finishes,
> per libpqrcv_endstreaming(), and it's no longer getting one.
> 
> (I have not read the protocol document to see if this is per spec;
> but spec or no, that's what libpqwalreceiver is expecting.)

Yeah, definitely.

The minimal fix seems to be to add an EndReplicationCommand() call in
the T_StartReplicationCmd case.  Testing this now ...

> The question that this raises is how the heck did that get past
> our test suites?  It seems like the error should have been obvious
> to even the most minimal testing.

... yeah, that's indeed an important question.  I'm going to guess that
the TAP suites are too forgiving :-(