Account for optimized MinMax aggregates during SS_finalize_plan. We are capable of optimizing MIN() and MAX() aggregates on indexed columns into subqueries that exploit the index, rather than the normal thing of scanning the whole table. When we do this, we replace the Aggref node(s) with Params referencing subquery outputs. Such Params really ought to be included in the per-plan-node extParam/allParam sets computed by SS_finalize_plan. However, we've never done so up to now because of an ancient implementation choice to perform that substitution during set_plan_references, which runs after SS_finalize_plan, so that SS_finalize_plan never sees these Params.
This seems like clearly a bug, yet there have been no field reports of problems that could trace to it. This may be because the types of Plan nodes that could contain Aggrefs do not have any of the rescan optimizations that are controlled by extParam/allParam. Nonetheless it seems certain to bite us someday, so let's fix it in a self-contained patch that can be back-patched if we find a case in which there's a live bug pre-v17. The cleanest fix would be to perform a separate tree walk to do these substitutions before SS_finalize_plan runs. That seems unattractive, first because a whole-tree mutation pass is expensive, and second because we lack infrastructure for visiting expression subtrees in a Plan tree, so that we'd need a new function knowing as much as SS_finalize_plan knows about that. I also considered swapping the order of SS_finalize_plan and set_plan_references, but that fell foul of various assumptions that seem tricky to fix. So the approach adopted here is to teach SS_finalize_plan itself to check for such Aggrefs. I refactored things a bit in setrefs.c to avoid having three copies of the code that does that. Given the lack of any currently-known bug, no test case here. Discussion: https://postgr.es/m/2391880.1689025...@sss.pgh.pa.us Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/d0d44049d1262aed2eee906d26af852948206db0 Modified Files -------------- src/backend/optimizer/plan/setrefs.c | 68 +++++++++++++++++++++------------- src/backend/optimizer/plan/subselect.c | 25 +++++++++++-- src/include/optimizer/planmain.h | 2 + 3 files changed, 66 insertions(+), 29 deletions(-)
