On 23/8/2023 12:37, Richard Guo wrote: > To fix it we may need to modify RelOptInfos for Path, BitmapHeapPath, > ForeignPath and CustomPath, and modify IndexOptInfos for IndexPath. It > seems that that is not easily done without postponing reparameterization > of paths until createplan.c. > > Attached is a patch which is v5 + fix for this new issue.
Having looked into the patch for a while, I couldn't answer to myself for some stupid questions:
Thanks for reviewing this patch! I think these are great questions.
1. If we postpone parameterization until the plan creation, why do we still copy the path node in the FLAT_COPY_PATH macros? Do we really need it?
Good point. The NestPath's origin inner path should not be referenced any more after the reparameterization, so it seems safe to adjust the path itself, without the need of a flat-copy. I've done that in v8 patch.
2. I see big switches on path nodes. May it be time to create a path_walker function? I recall some thread where such a suggestion was declined, but I don't remember why.
I'm not sure. But this seems a separate topic, so maybe it's better to discuss it separately?
3. Clause changing is postponed. Why does it not influence the calc_joinrel_size_estimate? We will use statistics on the parent table here. Am I wrong?
Hmm, I think the reparameterization does not change the estimated size/costs. Quoting the comment
* The cost, number of rows, width and parallel path properties depend upon * path->parent, which does not change during the translation.
Hi Tom, I'm wondering if you've had a chance to follow this issue. What do you think about the proposed patch?
