inherited GROUP BY is busted ... I need some help here

I wrote:

I've been chasing Chris Bitmead's coredump report from earlier today.
I find that it can be reproduced very easily. For example:
regression=> select f1 from int4_tbl group by f1;
< no problem >
regression=> select f1 from int4_tbl* group by f1;
< core dump >

We had tentatively agreed not to fix this for 6.5, but I got more
worried about it when I noticed that this particular simple case
worked in 6.4.2. I don't like regressing ... so I dug into it and
have just committed a fix.

It turns out that pretty much *anything* involving grouping or
aggregation would fail if the query used inheritance, because the
necessary preprocessing wasn't getting done in that case. I think
that's a big enough bug to justify fixing at this late date. (Besides,
the fixes do not change the non-inheritance case, so I don't think
I could have broken anything that was working...)

regards, tom lane

Tom, I can dig into this with you, if it is not already fixed.

I've been chasing Chris Bitmead's coredump report from earlier today.
I find that it can be reproduced very easily. For example:
regression=> select f1 from int4_tbl group by f1;
< no problem >
regression=> select f1 from int4_tbl* group by f1;
< core dump >

(You may get unstable behavior rather than a reliable core dump
if you are not configured --enable-cassert.)

The problem seems to be in optimizer/plan/planner.c, which is
responsible for creating the Sort and Group plan nodes needed to
implement GROUP BY. It also has to mark the lower plan's targetlist
items with resdom->reskey numbers so that the executor will know which
items to use for sort keys (cf. FormSortKeys in executor/nodeSort.c).
The trouble is that that latter marking is done in planner.c's
make_subplanTargetList(), which *is never invoked* for a query that
involves inheritance. union_planner() only calls it if the given plan
involves neither UNION nor inheritance. In the UNION case, recursion
into union_planner does the right thing, but not so in the inheritance
case.

I rewrote some of this code a couple months ago, but I find that 6.4.2
has similar problems, so at least I can say I didn't break it ;-).

It seems clear that at least some of the processing that union_planner
does in the simple case (the "else" part of its first big if-then-else)
also needs to be done in the inheritance case (and perhaps also in
the UNION case?). But I'm not sure exactly what. There's a lot going
on in this chunk of code, and I don't understand very much of it.
I could really use some advice...

regards, tom lane

-- 
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Bruce Momjian <maillist@candle.pha.pa.us> writes:

Tom, I can dig into this with you, if it is not already fixed.

It's at least partially fixed: the given test case does not coredump.
I think there are still problems with more complex combinations of
inheritance, UNION, and GROUP BY, however.

I have some more changes in that area that I do not want to risk
committing into 6.5.* ... after we split the tree I will commit them
and then we can see how well things work...

regards, tom lane