Re: BUG #17596: "invalid attribute number 11" when updating partitioned table with a MULTIEXPR_SUBLINK

PG Bug reporting form <noreply@postgresql.org> writes:
> ERROR:  XX000: invalid attribute number 11
> LOCATION:  slot_getsomeattrs_int, execTuples.c:1909

> I did some investigations. The current implementation, the update plans of
> different partitions use the same param id for the subplan param, but they
> correspond to different SubPlanStates during execution, SubPlanState are
> generated during ExecInitSubPlan and linked to ParamExecData->execPlan.
> Since the plans of multiple partitions share one Param, according to the
> execution order, the final execPlan will be set to the SubPlanState of the
> last partition in the InitPlan phase.
> And because the order of joins in different partition plans is different,
> the final SubPlanState->args does not match the expectation (some are
> OUTER_VAR, some are INNER_VAR), and an error is occurred (failed assertion
> if "--enable-cassert" and coredump)

Thanks for the report!  I find that this bug doesn't reproduce in v14 and
up, now that we got rid of inheritance_planner().  It is a live issue
before that though, because as you say MULTIEXPR_SUBLINK SubPlans can
do the wrong thing if their "args" lists aren't all identical.

I was confused for awhile as to why the problem hadn't emerged long
before, because the business with setting ParamExecData.execPlan
to point to a SubPlan is ancient.  I eventually realized that it's
safe in the context of initplans, because *those don't have any values
to be passed in*, so their args lists are always empty.  This means
that it doesn't matter if we clone an initplan SubPlan and let the
clones share output parameters, because they'll all be alike enough for
ExecSetParamPlan's purposes.  But it does matter for MULTIEXPR_SUBLINK,
which abused that ancient design by adding the possibility of passed-in
arguments.

So what we need to do is guarantee that MULTIEXPR_SUBLINKs don't
share output parameters.  Fortunately, this isn't too hard, because
that could only happen when inheritance_planner() clones an UPDATE
targetlist, and the stuff we need to change will all be at top level
of that targetlist.

Proposed patch against v13 attached; it'll need to be back-patched
as far as v10.  We don't need any of this logic in v14 and up,
but I'm thinking of putting a slightly modified version of the new
comment in nodeSubplan.c into HEAD, just to memorialize the issue.

			regards, tom lane