Re: postgres_fdw bug in 9.6

On Thu, Dec 8, 2016 at 10:28 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Robert Haas <robertmhaas@gmail.com> writes:
> > Maybe it would help for Jeff to use elog_node_display() to the nodes
> > that are causing the problem - e.g. outerpathkeys and innerpathkeys
> > and best_path->path_mergeclauses, or just best_path - at the point
> > where the error is thrown. That might give us enough information to
> > see what's broken.
>
> I'll be astonished if that's sufficient evidence.  We already know that
> the problem is that the input path doesn't claim to be sorted in a way
> that would match the merge clauses, but that doesn't tell us how such
> a path came to be generated (or, if it wasn't intentionally done, where
> the data structure got clobbered later).
>
> It's possible that setting a breakpoint at create_mergejoin_path and
> capturing stack traces for all calls would yield usable insight.  But
> there are likely to be lots of calls if this is an 8-way join query,
> and probably only a few are wrong.
>
> I'd much rather have a test case than try to debug this remotely.
> Bandwidth too low.
>

I didn't get an asserts on the assert-enabled build.

I have a test case where I made the fdw connect back to itself, and
stripped out all the objects that I could and still reproduce the case.  It
is large, 21MB compressed, 163MB uncompressed, so I am linking it here:

https://drive.google.com/open?id=0Bzqrh1SO9FcEZkpPM0JwUEMzcmc

When running this against and default configured 9.6.1 or 10devel-a73491e,
I get the error.

psql -U postgres -f <(xzcat combined_anon.sql.xz)

...

ERROR:  outer pathkeys do not match mergeclauses
STATEMENT:  explain update local1 set local19 = jj_join.local19 from
jj_join where local1.local12=jj_join.local12  and local1.local12 in
('ddd','bbb','aaa','abc');

Cheers,

Jeff