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3fc6e2d7f5
I've been saying we needed to do this for more than five years, and here it finally is. This patch removes the ever-growing tangle of spaghetti logic that grouping_planner() used to use to try to identify the best plan for post-scan/join query steps. Now, there is (nearly) independent consideration of each execution step, and entirely separate construction of Paths to represent each of the possible ways to do that step. We choose the best Path or set of Paths using the same add_path() logic that's been used inside query_planner() for years. In addition, this patch removes the old restriction that subquery_planner() could return only a single Plan. It now returns a RelOptInfo containing a set of Paths, just as query_planner() does, and the parent query level can use each of those Paths as the basis of a SubqueryScanPath at its level. This allows finding some optimizations that we missed before, wherein a subquery was capable of returning presorted data and thereby avoiding a sort in the parent level, making the overall cost cheaper even though delivering sorted output was not the cheapest plan for the subquery in isolation. (A couple of regression test outputs change in consequence of that. However, there is very little change in visible planner behavior overall, because the point of this patch is not to get immediate planning benefits but to create the infrastructure for future improvements.) There is a great deal left to do here. This patch unblocks a lot of planner work that was basically impractical in the old code structure, such as allowing FDWs to implement remote aggregation, or rewriting plan_set_operations() to allow consideration of multiple implementation orders for set operations. (The latter will likely require a full rewrite of plan_set_operations(); what I've done here is only to fix it to return Paths not Plans.) I have also left unfinished some localized refactoring in createplan.c and planner.c, because it was not necessary to get this patch to a working state. Thanks to Robert Haas, David Rowley, and Amit Kapila for review.
44 lines
1.7 KiB
C
44 lines
1.7 KiB
C
/*-------------------------------------------------------------------------
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*
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* subselect.h
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*
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* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/optimizer/subselect.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef SUBSELECT_H
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#define SUBSELECT_H
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#include "nodes/plannodes.h"
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#include "nodes/relation.h"
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extern void SS_process_ctes(PlannerInfo *root);
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extern JoinExpr *convert_ANY_sublink_to_join(PlannerInfo *root,
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SubLink *sublink,
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Relids available_rels);
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extern JoinExpr *convert_EXISTS_sublink_to_join(PlannerInfo *root,
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SubLink *sublink,
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bool under_not,
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Relids available_rels);
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extern Node *SS_replace_correlation_vars(PlannerInfo *root, Node *expr);
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extern Node *SS_process_sublinks(PlannerInfo *root, Node *expr, bool isQual);
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extern void SS_identify_outer_params(PlannerInfo *root);
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extern void SS_charge_for_initplans(PlannerInfo *root, RelOptInfo *final_rel);
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extern void SS_attach_initplans(PlannerInfo *root, Plan *plan);
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extern void SS_finalize_plan(PlannerInfo *root, Plan *plan);
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extern Param *SS_make_initplan_output_param(PlannerInfo *root,
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Oid resulttype, int32 resulttypmod,
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Oid resultcollation);
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extern void SS_make_initplan_from_plan(PlannerInfo *root,
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PlannerInfo *subroot, Plan *plan,
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Param *prm);
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extern Param *assign_nestloop_param_var(PlannerInfo *root, Var *var);
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extern Param *assign_nestloop_param_placeholdervar(PlannerInfo *root,
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PlaceHolderVar *phv);
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extern int SS_assign_special_param(PlannerInfo *root);
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#endif /* SUBSELECT_H */
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