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

On 2020-Oct-01, Peter Eisentraut wrote:

> On 2020-09-30 23:32, Tom Lane wrote:
> > 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.
> 
> What's the difference between this case and what the test suite is testing?
> Is it that it replicates between two databases on the same instance?

I don't know why the tests pass, but the message
  ERROR:  error reading result of streaming command: 
does appear in the logs after running src/test/subscription many times
(I see it in tests 001, 002, 013 and 014, apart from the new one in
100).  It's indeed surprising that these tests all pass!

I turned Henry's reproducer into the attached TAP test, and it does
reproduce the problem; but if I reduce the number of rows from 5000 to
1000, then it no longer does.  I don't quite see why this would be a
problem with a larger table only.  Do you?

The fix is the commented-out line in walsender.c; the test reliably
passes for me if I uncomment that, and the error message disappear from
the server logs in all the other tests.