Re: Don't overwrite scan key in systable_beginscan()

On Thu, Aug 8, 2024 at 2:46 AM Peter Eisentraut <peter(at)eisentraut(dot)org> wrote:
> When systable_beginscan() and systable_beginscan_ordered() choose an
> index scan, they remap the attribute numbers in the passed-in scan keys
> to the attribute numbers of the index, and then write those remapped
> attribute numbers back into the scan key passed by the caller. This
> second part is surprising and gratuitous. It means that a scan key
> cannot safely be used more than once (but it might sometimes work,
> depending on circumstances). Also, there is no value in providing these
> remapped attribute numbers back to the caller, since they can't do
> anything with that.
>
> I propose to fix that by making a copy of the scan keys passed by the
> caller and make the modifications there.

This does have the disadvantage of adding more palloc overhead.

--
Robert Haas
EDB: http://www.enterprisedb.com