diff options
| author | Tom Lane | 2025-06-20 19:55:12 +0000 |
|---|---|---|
| committer | Tom Lane | 2025-06-20 19:55:12 +0000 |
| commit | a16ef313f2c21225e89ddb9168f30601f21c7d07 (patch) | |
| tree | 1d41609cbf41cc6ccec085d8d2f4432f6ce2581f /src/include | |
| parent | 5861b1f343b52ac358912707788214fb8dc981e5 (diff) | |
Remove planner's have_dangerous_phv() join-order restriction.
Commit 85e5e222b, which added (a forerunner of) this logic,
argued that
Adding the necessary complexity to make this work doesn't seem like
it would be repaid in significantly better plans, because in cases
where such a PHV exists, there is probably a corresponding join order
constraint that would allow a good plan to be found without using the
star-schema exception.
The flaw in this claim is that there may be other join-order
restrictions that prevent us from finding a join order that doesn't
involve a "dangerous" PHV. In particular we now recognize that
small join_collapse_limit or from_collapse_limit could prevent it.
Therefore, let's bite the bullet and make the case work.
We don't have to extend the executor's support for nestloop parameters
as I thought at the time, because we can instead push the evaluation
of the placeholder's expression into the left-hand input of the
NestLoop node. So there's not really a lot of downside to this
solution, and giving the planner more join-order flexibility should
have value beyond just avoiding failure.
Having said that, there surely is a nonzero risk of introducing
new bugs. Since this failure mode escaped detection for ten years,
such cases don't seem common enough to justify a lot of risk.
Therefore, let's put this fix into master but leave the back branches
alone (for now anyway).
Bug: #18953
Reported-by: Alexander Lakhin <exclusion@gmail.com>
Diagnosed-by: Richard Guo <guofenglinux@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/18953-1c9883a9d4afeb30@postgresql.org
Diffstat (limited to 'src/include')
| -rw-r--r-- | src/include/optimizer/paramassign.h | 2 | ||||
| -rw-r--r-- | src/include/optimizer/paths.h | 2 |
2 files changed, 1 insertions, 3 deletions
diff --git a/src/include/optimizer/paramassign.h b/src/include/optimizer/paramassign.h index 59dcb1ff053..d30d20de299 100644 --- a/src/include/optimizer/paramassign.h +++ b/src/include/optimizer/paramassign.h @@ -30,7 +30,7 @@ extern Param *replace_nestloop_param_placeholdervar(PlannerInfo *root, extern void process_subquery_nestloop_params(PlannerInfo *root, List *subplan_params); extern List *identify_current_nestloop_params(PlannerInfo *root, - Relids leftrelids); + Path *leftpath); extern Param *generate_new_exec_param(PlannerInfo *root, Oid paramtype, int32 paramtypmod, Oid paramcollation); extern int assign_special_exec_param(PlannerInfo *root); diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h index a48c9721797..8410531f2d6 100644 --- a/src/include/optimizer/paths.h +++ b/src/include/optimizer/paths.h @@ -109,8 +109,6 @@ extern Relids add_outer_joins_to_relids(PlannerInfo *root, Relids input_relids, List **pushed_down_joins); extern bool have_join_order_restriction(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2); -extern bool have_dangerous_phv(PlannerInfo *root, - Relids outer_relids, Relids inner_params); extern void mark_dummy_rel(RelOptInfo *rel); extern void init_dummy_sjinfo(SpecialJoinInfo *sjinfo, Relids left_relids, Relids right_relids); |