mirror of
https://github.com/postgres/postgres.git
synced 2026-01-27 21:43:08 +03:00
a3179ab692
Up to now, remove_rel_from_query() has done a pretty shoddy job of updating our where-needed bitmaps (per-Var attr_needed and per-PlaceHolderVar ph_needed relid sets). It removed direct mentions of the to-be-removed baserel and outer join, which is the minimum amount of effort needed to keep the data structures self-consistent. But it didn't account for the fact that the removed join ON clause probably mentioned Vars of other relations, and those Vars might now not be needed as high up in the join tree as before. It's easy to show cases where this results in failing to remove a lower outer join that could also have been removed. To fix, recalculate the where-needed bitmaps from scratch after each successful join removal. This sounds expensive, but it seems to add only negligible planner runtime. (We cheat a little bit by preserving "relation 0" entries in the bitmaps, allowing us to skip re-scanning the targetlist and HAVING qual.) The submitted test case drew attention because we had successfully optimized away the lower join prior to v16. I suspect that that's somewhat accidental and there are related cases that were never optimized before and now can be. I've not tried to come up with one, though. Perhaps we should back-patch this into v16 and v17 to repair the performance regression. However, since it took a year for anyone to notice the problem, it can't be affecting too many people. Let's let the patch bake awhile in HEAD, and see if we get more complaints. Per bug #18627 from Mikaël Gourlaouen. No back-patch for now. Discussion: https://postgr.es/m/18627-44f950eb6a8416c2@postgresql.org
35 lines
1.2 KiB
C
35 lines
1.2 KiB
C
/*-------------------------------------------------------------------------
|
|
*
|
|
* placeholder.h
|
|
* prototypes for optimizer/util/placeholder.c.
|
|
*
|
|
*
|
|
* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
|
|
* Portions Copyright (c) 1994, Regents of the University of California
|
|
*
|
|
* src/include/optimizer/placeholder.h
|
|
*
|
|
*-------------------------------------------------------------------------
|
|
*/
|
|
#ifndef PLACEHOLDER_H
|
|
#define PLACEHOLDER_H
|
|
|
|
#include "nodes/pathnodes.h"
|
|
|
|
|
|
extern PlaceHolderVar *make_placeholder_expr(PlannerInfo *root, Expr *expr,
|
|
Relids phrels);
|
|
extern PlaceHolderInfo *find_placeholder_info(PlannerInfo *root,
|
|
PlaceHolderVar *phv);
|
|
extern void find_placeholders_in_jointree(PlannerInfo *root);
|
|
extern void fix_placeholder_input_needed_levels(PlannerInfo *root);
|
|
extern void rebuild_placeholder_attr_needed(PlannerInfo *root);
|
|
extern void add_placeholders_to_base_rels(PlannerInfo *root);
|
|
extern void add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
|
|
RelOptInfo *outer_rel, RelOptInfo *inner_rel,
|
|
SpecialJoinInfo *sjinfo);
|
|
extern bool contain_placeholder_references_to(PlannerInfo *root, Node *clause,
|
|
int relid);
|
|
|
|
#endif /* PLACEHOLDER_H */
|