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postgresql/src/include/optimizer/cost.h
Tomas Vondra d2d8a229bc Implement Incremental Sort 
Incremental Sort is an optimized variant of multikey sort for cases when
the input is already sorted by a prefix of the requested sort keys. For
example when the relation is already sorted by (key1, key2) and we need
to sort it by (key1, key2, key3) we can simply split the input rows into
groups having equal values in (key1, key2), and only sort/compare the
remaining column key3.

This has a number of benefits:

- Reduced memory consumption, because only a single group (determined by
  values in the sorted prefix) needs to be kept in memory. This may also
  eliminate the need to spill to disk.

- Lower startup cost, because Incremental Sort produce results after each
  prefix group, which is beneficial for plans where startup cost matters
  (like for example queries with LIMIT clause).

We consider both Sort and Incremental Sort, and decide based on costing.

The implemented algorithm operates in two different modes:

- Fetching a minimum number of tuples without check of equality on the
  prefix keys, and sorting on all columns when safe.

- Fetching all tuples for a single prefix group and then sorting by
  comparing only the remaining (non-prefix) keys.

We always start in the first mode, and employ a heuristic to switch into
the second mode if we believe it's beneficial - the goal is to minimize
the number of unnecessary comparions while keeping memory consumption
below work_mem.

This is a very old patch series. The idea was originally proposed by
Alexander Korotkov back in 2013, and then revived in 2017. In 2018 the
patch was taken over by James Coleman, who wrote and rewrote most of the
current code.

There were many reviewers/contributors since 2013 - I've done my best to
pick the most active ones, and listed them in this commit message.

Author: James Coleman, Alexander Korotkov
Reviewed-by: Tomas Vondra, Andreas Karlsson, Marti Raudsepp, Peter Geoghegan, Robert Haas, Thomas Munro, Antonin Houska, Andres Freund, Alexander Kuzmenkov
Discussion: https://postgr.es/m/CAPpHfdscOX5an71nHd8WSUH6GNOCf=V7wgDaTXdDd9=goN-gfA@mail.gmail.com
Discussion: https://postgr.es/m/CAPpHfds1waRZ=NOmueYq0sx1ZSCnt+5QJvizT8ndT2=etZEeAQ@mail.gmail.com
2020-04-06 21:35:10 +02:00

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/*-------------------------------------------------------------------------
*
* cost.h
* prototypes for costsize.c and clausesel.c.
*
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/optimizer/cost.h
*
*-------------------------------------------------------------------------
*/
#ifndef COST_H
#define COST_H
#include "nodes/pathnodes.h"
#include "nodes/plannodes.h"
/* defaults for costsize.c's Cost parameters */
/* NB: cost-estimation code should use the variables, not these constants! */
/* If you change these, update backend/utils/misc/postgresql.sample.conf */
#define DEFAULT_SEQ_PAGE_COST 1.0
#define DEFAULT_RANDOM_PAGE_COST 4.0
#define DEFAULT_CPU_TUPLE_COST 0.01
#define DEFAULT_CPU_INDEX_TUPLE_COST 0.005
#define DEFAULT_CPU_OPERATOR_COST 0.0025
#define DEFAULT_PARALLEL_TUPLE_COST 0.1
#define DEFAULT_PARALLEL_SETUP_COST 1000.0
#define DEFAULT_EFFECTIVE_CACHE_SIZE 524288 /* measured in pages */
typedef enum
{
CONSTRAINT_EXCLUSION_OFF, /* do not use c_e */
CONSTRAINT_EXCLUSION_ON, /* apply c_e to all rels */
CONSTRAINT_EXCLUSION_PARTITION /* apply c_e to otherrels only */
} ConstraintExclusionType;
/*
* prototypes for costsize.c
* routines to compute costs and sizes
*/
/* parameter variables and flags (see also optimizer.h) */
extern PGDLLIMPORT Cost disable_cost;
extern PGDLLIMPORT int max_parallel_workers_per_gather;
extern PGDLLIMPORT bool enable_seqscan;
extern PGDLLIMPORT bool enable_indexscan;
extern PGDLLIMPORT bool enable_indexonlyscan;
extern PGDLLIMPORT bool enable_bitmapscan;
extern PGDLLIMPORT bool enable_tidscan;
extern PGDLLIMPORT bool enable_sort;
extern PGDLLIMPORT bool enable_incrementalsort;
extern PGDLLIMPORT bool enable_hashagg;
extern PGDLLIMPORT bool enable_hashagg_disk;
extern PGDLLIMPORT bool enable_groupingsets_hash_disk;
extern PGDLLIMPORT bool enable_nestloop;
extern PGDLLIMPORT bool enable_material;
extern PGDLLIMPORT bool enable_mergejoin;
extern PGDLLIMPORT bool enable_hashjoin;
extern PGDLLIMPORT bool enable_gathermerge;
extern PGDLLIMPORT bool enable_partitionwise_join;
extern PGDLLIMPORT bool enable_partitionwise_aggregate;
extern PGDLLIMPORT bool enable_parallel_append;
extern PGDLLIMPORT bool enable_parallel_hash;
extern PGDLLIMPORT bool enable_partition_pruning;
extern PGDLLIMPORT int constraint_exclusion;
extern double index_pages_fetched(double tuples_fetched, BlockNumber pages,
double index_pages, PlannerInfo *root);
extern void cost_seqscan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
ParamPathInfo *param_info);
extern void cost_samplescan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
ParamPathInfo *param_info);
extern void cost_index(IndexPath *path, PlannerInfo *root,
double loop_count, bool partial_path);
extern void cost_bitmap_heap_scan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
ParamPathInfo *param_info,
Path *bitmapqual, double loop_count);
extern void cost_bitmap_and_node(BitmapAndPath *path, PlannerInfo *root);
extern void cost_bitmap_or_node(BitmapOrPath *path, PlannerInfo *root);
extern void cost_bitmap_tree_node(Path *path, Cost *cost, Selectivity *selec);
extern void cost_tidscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, List *tidquals, ParamPathInfo *param_info);
extern void cost_subqueryscan(SubqueryScanPath *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info);
extern void cost_functionscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info);
extern void cost_valuesscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info);
extern void cost_tablefuncscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info);
extern void cost_ctescan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info);
extern void cost_namedtuplestorescan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info);
extern void cost_resultscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info);
extern void cost_recursive_union(Path *runion, Path *nrterm, Path *rterm);
extern void cost_sort(Path *path, PlannerInfo *root,
List *pathkeys, Cost input_cost, double tuples, int width,
Cost comparison_cost, int sort_mem,
double limit_tuples);
extern void cost_incremental_sort(Path *path,
PlannerInfo *root, List *pathkeys, int presorted_keys,
Cost input_startup_cost, Cost input_total_cost,
double input_tuples, int width, Cost comparison_cost, int sort_mem,
double limit_tuples);
extern void cost_append(AppendPath *path);
extern void cost_merge_append(Path *path, PlannerInfo *root,
List *pathkeys, int n_streams,
Cost input_startup_cost, Cost input_total_cost,
double tuples);
extern void cost_material(Path *path,
Cost input_startup_cost, Cost input_total_cost,
double tuples, int width);
extern void cost_agg(Path *path, PlannerInfo *root,
AggStrategy aggstrategy, const AggClauseCosts *aggcosts,
int numGroupCols, double numGroups,
List *quals,
Cost input_startup_cost, Cost input_total_cost,
double input_tuples, double input_width);
extern void cost_windowagg(Path *path, PlannerInfo *root,
List *windowFuncs, int numPartCols, int numOrderCols,
Cost input_startup_cost, Cost input_total_cost,
double input_tuples);
extern void cost_group(Path *path, PlannerInfo *root,
int numGroupCols, double numGroups,
List *quals,
Cost input_startup_cost, Cost input_total_cost,
double input_tuples);
extern void initial_cost_nestloop(PlannerInfo *root,
JoinCostWorkspace *workspace,
JoinType jointype,
Path *outer_path, Path *inner_path,
JoinPathExtraData *extra);
extern void final_cost_nestloop(PlannerInfo *root, NestPath *path,
JoinCostWorkspace *workspace,
JoinPathExtraData *extra);
extern void initial_cost_mergejoin(PlannerInfo *root,
JoinCostWorkspace *workspace,
JoinType jointype,
List *mergeclauses,
Path *outer_path, Path *inner_path,
List *outersortkeys, List *innersortkeys,
JoinPathExtraData *extra);
extern void final_cost_mergejoin(PlannerInfo *root, MergePath *path,
JoinCostWorkspace *workspace,
JoinPathExtraData *extra);
extern void initial_cost_hashjoin(PlannerInfo *root,
JoinCostWorkspace *workspace,
JoinType jointype,
List *hashclauses,
Path *outer_path, Path *inner_path,
JoinPathExtraData *extra,
bool parallel_hash);
extern void final_cost_hashjoin(PlannerInfo *root, HashPath *path,
JoinCostWorkspace *workspace,
JoinPathExtraData *extra);
extern void cost_gather(GatherPath *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info, double *rows);
extern void cost_gather_merge(GatherMergePath *path, PlannerInfo *root,
RelOptInfo *rel, ParamPathInfo *param_info,
Cost input_startup_cost, Cost input_total_cost,
double *rows);
extern void cost_subplan(PlannerInfo *root, SubPlan *subplan, Plan *plan);
extern void cost_qual_eval(QualCost *cost, List *quals, PlannerInfo *root);
extern void cost_qual_eval_node(QualCost *cost, Node *qual, PlannerInfo *root);
extern void compute_semi_anti_join_factors(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
JoinType jointype,
SpecialJoinInfo *sjinfo,
List *restrictlist,
SemiAntiJoinFactors *semifactors);
extern void set_baserel_size_estimates(PlannerInfo *root, RelOptInfo *rel);
extern double get_parameterized_baserel_size(PlannerInfo *root,
RelOptInfo *rel,
List *param_clauses);
extern double get_parameterized_joinrel_size(PlannerInfo *root,
RelOptInfo *rel,
Path *outer_path,
Path *inner_path,
SpecialJoinInfo *sjinfo,
List *restrict_clauses);
extern void set_joinrel_size_estimates(PlannerInfo *root, RelOptInfo *rel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel,
SpecialJoinInfo *sjinfo,
List *restrictlist);
extern void set_subquery_size_estimates(PlannerInfo *root, RelOptInfo *rel);
extern void set_function_size_estimates(PlannerInfo *root, RelOptInfo *rel);
extern void set_values_size_estimates(PlannerInfo *root, RelOptInfo *rel);
extern void set_cte_size_estimates(PlannerInfo *root, RelOptInfo *rel,
double cte_rows);
extern void set_tablefunc_size_estimates(PlannerInfo *root, RelOptInfo *rel);
extern void set_namedtuplestore_size_estimates(PlannerInfo *root, RelOptInfo *rel);
extern void set_result_size_estimates(PlannerInfo *root, RelOptInfo *rel);
extern void set_foreign_size_estimates(PlannerInfo *root, RelOptInfo *rel);
extern PathTarget *set_pathtarget_cost_width(PlannerInfo *root, PathTarget *target);
extern double compute_bitmap_pages(PlannerInfo *root, RelOptInfo *baserel,
Path *bitmapqual, int loop_count, Cost *cost, double *tuple);
#endif /* COST_H */
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