Re: Can rs_cindex be < 0 for bitmap heap scans?

Em qua., 18 de dez. de 2024 às 23:50, Richard Guo <guofenglinux(at)gmail(dot)com>
escreveu:

> On Thu, Dec 19, 2024 at 8:18 AM Melanie Plageman
> <melanieplageman(at)gmail(dot)com> wrote:
> > I pushed the straightforward option for now so that it's fixed.
>
> I think this binary search code now has a risk of underflow. If 'mid'
> is calculated as zero, the second 'if' branch will cause 'end' to
> underflow.
>
> Maybe we need to do something like below.
>
> --- a/src/backend/access/heap/heapam_handler.c
> +++ b/src/backend/access/heap/heapam_handler.c
> @@ -2600,7 +2600,11 @@ SampleHeapTupleVisible(TableScanDesc scan, Buffer
> buffer,
> if (tupoffset == curoffset)
> return true;
> else if (tupoffset < curoffset)
> + {
> + if (mid == 0)
> + return false;
> end = mid - 1;
> + }
> else
> start = mid + 1;
> }
>
> Alternatively, we can revert 'start' and 'end' to signed int as they
> were before.
>
How would it be *signed*?
Wouldn't overflow happen in this case?
rs_tuples now can be

UINT_MAX = 4294967295

best regards,
Ranier Vilela