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

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

From
Tom Lane
Date:
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

Re: [HACKERS] inherited GROUP BY is busted ... I need some help here

From
Tom Lane
Date:
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

Re: [HACKERS] inherited GROUP BY is busted ... I need some help here

From
Bruce Momjian
Date:
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
> 
> 


--  Bruce Momjian                        |  http://www.op.net/~candle maillist@candle.pha.pa.us            |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026

Re: [HACKERS] inherited GROUP BY is busted ... I need some help here

From
Bruce Momjian
Date:
Tom, is this still an open item?


> 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
> 
> 


--  Bruce Momjian                        |  http://www.op.net/~candle maillist@candle.pha.pa.us            |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026

Re: [HACKERS] inherited GROUP BY is busted ... I need some help here

From
Tom Lane
Date:
Bruce Momjian <maillist@candle.pha.pa.us> writes:
> Tom, is this still an open item?

That particular coredump seems to be fixed.  There might be some other
problems lurking with inherited queries, but this thread can be
written off I think...

>> 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.)
        regards, tom lane