Re: [BUG] (firsttupleslot)==NULL is redundant or is possible null dereference?

On Fri, Nov 22, 2019 at 10:32:11PM +0000, Ranier Vilela wrote:
>Hi,
>This is real bug? firsttupleslot == NULL.
>

Ranier, I don't want to be rude, but I personally am getting a bit
annoyed by this torrent of bug reports that are essentially just a bunch
of copy-pasted chunks of code, without any specification of bench,
position in the file, etc.

And more importantly, without any clear explanation why you think it is
a bug (or even a demonstration of an issue), and "Is this a bug?"

>\backend\executor\nodeGroup.c
> if (TupIsNull(firsttupleslot))
> {
> outerslot = ExecProcNode(outerPlanState(node));
> if (TupIsNull(outerslot))
> {
> /* empty input, so return nothing */
> node->grp_done = true;
> return NULL;
> }
> /* Copy tuple into firsttupleslot */
> ExecCopySlot(firsttupleslot, outerslot);
>
>include\executor\tuptable.h:
>#define TupIsNull(slot) \
> ((slot) == NULL || TTS_EMPTY(slot))
>
>static inline TupleTableSlot *
>ExecCopySlot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
>{
> Assert(!TTS_EMPTY(srcslot));
>
> dstslot->tts_ops->copyslot(dstslot, srcslot);
>
> return dstslot;
>}
>

And why do you think this is a bug? Immediately before the part of code
you copied we have this:

/*
* The ScanTupleSlot holds the (copied) first tuple of each group.
*/
firsttupleslot = node->ss.ss_ScanTupleSlot;

And node->ss.ss_ScanTupleSlot is expected to be non-NULL. So the initial
assumption that firsttupleslot is NULL is incorrect.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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