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Provide a facility that (1) can be used to stabilize certain plan choices so that the planner cannot reverse course without authorization and (2) can be used by knowledgeable users to insist on plan choices contrary to what the planner believes best. In both cases, terrible outcomes are possible: users should think twice and perhaps three times before constraining the planner's ability to do as it thinks best; nevertheless, there are problems that are much more easily solved with these facilities than without them. This patch takes the approach of analyzing a finished plan to produce textual output, which we call "plan advice", that describes key decisions made during plan; if that plan advice is provided during future planning cycles, it will force those key decisions to be made in the same way. Not all planner decisions can be controlled using advice; for example, decisions about how to perform aggregation are currently out of scope, as is choice of sort order. Plan advice can also be edited by the user, or even written from scratch in simple cases, making it possible to generate outcomes that the planner would not have produced. Partial advice can be provided to control some planner outcomes but not others. Currently, plan advice is focused only on specific outcomes, such as the choice to use a sequential scan for a particular relation, and not on estimates that might contribute to those outcomes, such as a possibly-incorrect selectivity estimate. While it would be useful to users to be able to provide plan advice that affects selectivity estimates or other aspects of costing, that is out of scope for this commit. Reviewed-by: Lukas Fittl <lukas@fittl.com> Reviewed-by: Jakub Wartak <jakub.wartak@enterprisedb.com> Reviewed-by: Greg Burd <greg@burd.me> Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com> Reviewed-by: Haibo Yan <tristan.yim@gmail.com> Reviewed-by: Dian Fay <di@nmfay.com> Reviewed-by: Ajay Pal <ajay.pal.k@gmail.com> Reviewed-by: John Naylor <johncnaylorls@gmail.com> Reviewed-by: Alexandra Wang <alexandra.wang.oss@gmail.com> Discussion: http://postgr.es/m/CA+TgmoZ-Jh1T6QyWoCODMVQdhTUPYkaZjWztzP1En4=ZHoKPzw@mail.gmail.com
52 lines
1.4 KiB
C
52 lines
1.4 KiB
C
/*-------------------------------------------------------------------------
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*
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* pgpa_identifier.h
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* create appropriate identifiers for range table entries
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*
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* Copyright (c) 2016-2026, PostgreSQL Global Development Group
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*
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* contrib/pg_plan_advice/pgpa_identifier.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PGPA_IDENTIFIER_H
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#define PGPA_IDENTIFIER_H
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#include "nodes/pathnodes.h"
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#include "nodes/plannodes.h"
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typedef struct pgpa_identifier
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{
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const char *alias_name;
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int occurrence;
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const char *partnsp;
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const char *partrel;
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const char *plan_name;
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} pgpa_identifier;
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/* Convenience function for comparing possibly-NULL strings. */
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static inline bool
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strings_equal_or_both_null(const char *a, const char *b)
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{
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if (a == b)
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return true;
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else if (a == NULL || b == NULL)
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return false;
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else
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return strcmp(a, b) == 0;
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}
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extern const char *pgpa_identifier_string(const pgpa_identifier *rid);
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extern void pgpa_compute_identifier_by_rti(PlannerInfo *root, Index rti,
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pgpa_identifier *rid);
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extern int pgpa_compute_identifiers_by_relids(PlannerInfo *root,
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Bitmapset *relids,
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pgpa_identifier *rids);
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extern pgpa_identifier *pgpa_create_identifiers_for_planned_stmt(PlannedStmt *pstmt);
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extern Index pgpa_compute_rti_from_identifier(int rtable_length,
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pgpa_identifier *rt_identifiers,
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pgpa_identifier *rid);
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#endif
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