Delay qp_callback processing till after join removal. Commit 2ebf25e7d left query_planner's qp_callback call where it had been historically, but that turns out to be a bad idea. It means that the code reached via qp_callback is subject to the must-be-able-to-restart rule created by looping back after join removal. We found one place that fails that requirement: adjust_group_pathkeys_for_groupagg sets Aggref.aggpresorted flags, and there's nothing that will reset those in case of a query_planner restart, yet the selected set of Aggrefs can change. There might be other places with similar issues.
Fortunately, qp_callback's main charter is to compute/update pathkey values, and that is not something that join removal depends on or should depend on. (Whether join removal is valid is surely not dependent on what order the rel might get scanned in.) Nothing else within the restart loop depends on it either --- in other words, the existing placement was a bit random to begin with. So we can fix this problem just by moving that call to below the restart loop. That costs nothing, indeed it saves some cycles by not having to do that processing more than once. And removing an unstated requirement from code that's not directly called by query_planner should help forestall future bugs. While the known bug only exists in v18 and up (older branches lack the aggpresorted optimization), I've chosen to back-patch the code change to v16 like 2ebf25e7d was. This is the sort of API requirement that we don't really want to be different across branches. Reported-by: shihao zhong <[email protected]> Author: Tom Lane <[email protected]> Reviewed-by: shihao zhong <[email protected]> Discussion: https://postgr.es/m/CAGRkXqSOAT1yop44B8jwacL_91rxK=quou8of3nlmb9ngao...@mail.gmail.com Backpatch-through: 16 Branch ------ REL_17_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/1000f7b14a1dad0acf1c82cb8fdd5a7a8ab1df0b Modified Files -------------- src/backend/optimizer/plan/planmain.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)
