On 2021-Jun-09, Tom Lane wrote: > I wrote: > > It turns out that the problem is specific to SELECT FOR UPDATE, and > > it happens because nodeLockRows is not careful to shut down the > > EvalPlanQual mechanism it uses before returning NULL at the end of > > a scan. If EPQ has been fired, it'll be holding a tuple slot > > referencing whatever tuple it was last asked about. The attached > > trivial patch seems to take care of the issue nicely, while adding > > little if any overhead. (A repeat call to EvalPlanQualEnd doesn't > > do much.)
Thanks for researching that -- good find. > BTW, to be clear: I think Alvaro's change is also necessary. > If libpq is going to silently do something different in pipeline > mode than it does in normal mode, it should strive to minimize > the semantic difference. exec_simple_query includes a PortalDrop, > so we'd best do the same in pipeline mode. But this LockRows > misbehavior would be visible in other operating modes anyway. Agreed. I'll get it pushed after the patch I'm currently looking at. -- Álvaro Herrera 39°49'30"S 73°17'W
