On Wed, Jan 22, 2020 at 1:09 PM Floris Van Nee <florisvan...@optiver.com> wrote: > The loose index scan shouldn't return a tuple twice. It should only be able > to skip 'further', so that shouldn't be a problem. Out of curiosity, why > can't index scans return the same tuple twice? Is there something in the > executor that isn't able to handle this?
I have no reason to believe that the executor has a problem with index scans that return a tuple more than once, aside from the very obvious: in general, that will often be wrong. It might not be wrong when the scan happens to be input to a unique node anyway, or something like that. I'm not particularly concerned about it. Just wanted to be clear on our assumptions for loose index scans -- if loose index scans were allowed to return a tuple more than once, then that would at least have to at least be considered in the wider context of the executor (but apparently they're not, so no need to worry about it). This may have been mentioned somewhere already. If it is then I must have missed it. -- Peter Geoghegan
