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postgresql/src/backend/optimizer/path/costsize.c

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/*-------------------------------------------------------------------------
*
* costsize.c
* Routines to compute (and set) relation sizes and path costs
*
* Path costs are measured in arbitrary units established by these basic
* parameters:
*
* seq_page_cost Cost of a sequential page fetch
* random_page_cost Cost of a non-sequential page fetch
* cpu_tuple_cost Cost of typical CPU time to process a tuple
* cpu_index_tuple_cost Cost of typical CPU time to process an index tuple
* cpu_operator_cost Cost of CPU time to execute an operator or function
* parallel_tuple_cost Cost of CPU time to pass a tuple from worker to leader backend
* parallel_setup_cost Cost of setting up shared memory for parallelism
*
* We expect that the kernel will typically do some amount of read-ahead
* optimization; this in conjunction with seek costs means that seq_page_cost
* is normally considerably less than random_page_cost. (However, if the
* database is fully cached in RAM, it is reasonable to set them equal.)
*
* We also use a rough estimate "effective_cache_size" of the number of
* disk pages in Postgres + OS-level disk cache. (We can't simply use
* NBuffers for this purpose because that would ignore the effects of
* the kernel's disk cache.)
*
* Obviously, taking constants for these values is an oversimplification,
* but it's tough enough to get any useful estimates even at this level of
* detail. Note that all of these parameters are user-settable, in case
* the default values are drastically off for a particular platform.
*
* seq_page_cost and random_page_cost can also be overridden for an individual
* tablespace, in case some data is on a fast disk and other data is on a slow
* disk. Per-tablespace overrides never apply to temporary work files such as
* an external sort or a materialize node that overflows work_mem.
*
* We compute two separate costs for each path:
* total_cost: total estimated cost to fetch all tuples
* startup_cost: cost that is expended before first tuple is fetched
* In some scenarios, such as when there is a LIMIT or we are implementing
* an EXISTS(...) sub-select, it is not necessary to fetch all tuples of the
* path's result. A caller can estimate the cost of fetching a partial
* result by interpolating between startup_cost and total_cost. In detail:
* actual_cost = startup_cost +
* (total_cost - startup_cost) * tuples_to_fetch / path->rows;
* Note that a base relation's rows count (and, by extension, plan_rows for
* plan nodes below the LIMIT node) are set without regard to any LIMIT, so
* that this equation works properly. (Note: while path->rows is never zero
* for ordinary relations, it is zero for paths for provably-empty relations,
* so beware of division-by-zero.) The LIMIT is applied as a top-level
* plan node.
*
* For largely historical reasons, most of the routines in this module use
* the passed result Path only to store their results (rows, startup_cost and
* total_cost) into. All the input data they need is passed as separate
* parameters, even though much of it could be extracted from the Path.
* An exception is made for the cost_XXXjoin() routines, which expect all
* the other fields of the passed XXXPath to be filled in, and similarly
* cost_index() assumes the passed IndexPath is valid except for its output
* values.
*
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/backend/optimizer/path/costsize.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <math.h>
#include "access/amapi.h"
#include "access/htup_details.h"
#include "access/tsmapi.h"
#include "executor/executor.h"
#include "executor/nodeAgg.h"
#include "executor/nodeHash.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/optimizer.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/placeholder.h"
#include "optimizer/plancat.h"
#include "optimizer/planmain.h"
#include "optimizer/restrictinfo.h"
#include "parser/parsetree.h"
#include "utils/lsyscache.h"
#include "utils/selfuncs.h"
#include "utils/spccache.h"
#include "utils/tuplesort.h"
#define LOG2(x) (log(x) / 0.693147180559945)
/*
* Append and MergeAppend nodes are less expensive than some other operations
* which use cpu_tuple_cost; instead of adding a separate GUC, estimate the
* per-tuple cost as cpu_tuple_cost multiplied by this value.
*/
#define APPEND_CPU_COST_MULTIPLIER 0.5
double seq_page_cost = DEFAULT_SEQ_PAGE_COST;
double random_page_cost = DEFAULT_RANDOM_PAGE_COST;
double cpu_tuple_cost = DEFAULT_CPU_TUPLE_COST;
double cpu_index_tuple_cost = DEFAULT_CPU_INDEX_TUPLE_COST;
double cpu_operator_cost = DEFAULT_CPU_OPERATOR_COST;
double parallel_tuple_cost = DEFAULT_PARALLEL_TUPLE_COST;
double parallel_setup_cost = DEFAULT_PARALLEL_SETUP_COST;
int effective_cache_size = DEFAULT_EFFECTIVE_CACHE_SIZE;
Cost disable_cost = 1.0e10;
int max_parallel_workers_per_gather = 2;
bool enable_seqscan = true;
bool enable_indexscan = true;
bool enable_indexonlyscan = true;
bool enable_bitmapscan = true;
bool enable_tidscan = true;
bool enable_sort = true;
bool enable_incremental_sort = true;
bool enable_hashagg = true;
bool enable_nestloop = true;
bool enable_material = true;
bool enable_mergejoin = true;
bool enable_hashjoin = true;
bool enable_gathermerge = true;
bool enable_partitionwise_join = false;
bool enable_partitionwise_aggregate = false;
bool enable_parallel_append = true;
bool enable_parallel_hash = true;
bool enable_partition_pruning = true;
typedef struct
{
PlannerInfo *root;
QualCost total;
} cost_qual_eval_context;
static List *extract_nonindex_conditions(List *qual_clauses, List *indexclauses);
static MergeScanSelCache *cached_scansel(PlannerInfo *root,
RestrictInfo *rinfo,
PathKey *pathkey);
static void cost_rescan(PlannerInfo *root, Path *path,
Cost *rescan_startup_cost, Cost *rescan_total_cost);
static bool cost_qual_eval_walker(Node *node, cost_qual_eval_context *context);
static void get_restriction_qual_cost(PlannerInfo *root, RelOptInfo *baserel,
ParamPathInfo *param_info,
QualCost *qpqual_cost);
static bool has_indexed_join_quals(NestPath *joinpath);
static double approx_tuple_count(PlannerInfo *root, JoinPath *path,
List *quals);
static double calc_joinrel_size_estimate(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel,
double outer_rows,
double inner_rows,
SpecialJoinInfo *sjinfo,
List *restrictlist);
static Selectivity get_foreign_key_join_selectivity(PlannerInfo *root,
Relids outer_relids,
Relids inner_relids,
SpecialJoinInfo *sjinfo,
List **restrictlist);
static Cost append_nonpartial_cost(List *subpaths, int numpaths,
int parallel_workers);
static void set_rel_width(PlannerInfo *root, RelOptInfo *rel);
static double relation_byte_size(double tuples, int width);
static double page_size(double tuples, int width);
static double get_parallel_divisor(Path *path);
/*
* clamp_row_est
* Force a row-count estimate to a sane value.
*/
double
clamp_row_est(double nrows)
{
/*
* Force estimate to be at least one row, to make explain output look
* better and to avoid possible divide-by-zero when interpolating costs.
* Make it an integer, too.
*/
if (nrows <= 1.0)
nrows = 1.0;
else
nrows = rint(nrows);
return nrows;
}
/*
* cost_seqscan
* Determines and returns the cost of scanning a relation sequentially.
*
* 'baserel' is the relation to be scanned
* 'param_info' is the ParamPathInfo if this is a parameterized path, else NULL
*/
void
cost_seqscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info)
{
Cost startup_cost = 0;
Cost cpu_run_cost;
Cost disk_run_cost;
double spc_seq_page_cost;
QualCost qpqual_cost;
Cost cpu_per_tuple;
/* Should only be applied to base relations */
Assert(baserel->relid > 0);
Assert(baserel->rtekind == RTE_RELATION);
/* Mark the path with the correct row estimate */
if (param_info)
path->rows = param_info->ppi_rows;
else
path->rows = baserel->rows;
if (!enable_seqscan)
startup_cost += disable_cost;
/* fetch estimated page cost for tablespace containing table */
get_tablespace_page_costs(baserel->reltablespace,
NULL,
&spc_seq_page_cost);
/*
* disk costs
*/
disk_run_cost = spc_seq_page_cost * baserel->pages;
/* CPU costs */
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
startup_cost += qpqual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple;
cpu_run_cost = cpu_per_tuple * baserel->tuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->pathtarget->cost.startup;
cpu_run_cost += path->pathtarget->cost.per_tuple * path->rows;
/* Adjust costing for parallelism, if used. */
if (path->parallel_workers > 0)
{
double parallel_divisor = get_parallel_divisor(path);
/* The CPU cost is divided among all the workers. */
cpu_run_cost /= parallel_divisor;
/*
* It may be possible to amortize some of the I/O cost, but probably
* not very much, because most operating systems already do aggressive
* prefetching. For now, we assume that the disk run cost can't be
* amortized at all.
*/
/*
* In the case of a parallel plan, the row count needs to represent
* the number of tuples processed per worker.
*/
path->rows = clamp_row_est(path->rows / parallel_divisor);
}
path->startup_cost = startup_cost;
path->total_cost = startup_cost + cpu_run_cost + disk_run_cost;
}
/*
* cost_samplescan
* Determines and returns the cost of scanning a relation using sampling.
*
* 'baserel' is the relation to be scanned
* 'param_info' is the ParamPathInfo if this is a parameterized path, else NULL
*/
void
cost_samplescan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info)
{
Cost startup_cost = 0;
Cost run_cost = 0;
RangeTblEntry *rte;
TableSampleClause *tsc;
TsmRoutine *tsm;
double spc_seq_page_cost,
spc_random_page_cost,
spc_page_cost;
QualCost qpqual_cost;
Cost cpu_per_tuple;
/* Should only be applied to base relations with tablesample clauses */
Assert(baserel->relid > 0);
rte = planner_rt_fetch(baserel->relid, root);
Assert(rte->rtekind == RTE_RELATION);
tsc = rte->tablesample;
Assert(tsc != NULL);
tsm = GetTsmRoutine(tsc->tsmhandler);
/* Mark the path with the correct row estimate */
if (param_info)
path->rows = param_info->ppi_rows;
else
path->rows = baserel->rows;
/* fetch estimated page cost for tablespace containing table */
get_tablespace_page_costs(baserel->reltablespace,
&spc_random_page_cost,
&spc_seq_page_cost);
/* if NextSampleBlock is used, assume random access, else sequential */
spc_page_cost = (tsm->NextSampleBlock != NULL) ?
spc_random_page_cost : spc_seq_page_cost;
/*
* disk costs (recall that baserel->pages has already been set to the
* number of pages the sampling method will visit)
*/
run_cost += spc_page_cost * baserel->pages;
/*
* CPU costs (recall that baserel->tuples has already been set to the
* number of tuples the sampling method will select). Note that we ignore
* execution cost of the TABLESAMPLE parameter expressions; they will be
* evaluated only once per scan, and in most usages they'll likely be
* simple constants anyway. We also don't charge anything for the
* calculations the sampling method might do internally.
*/
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
startup_cost += qpqual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple;
run_cost += cpu_per_tuple * baserel->tuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->pathtarget->cost.startup;
run_cost += path->pathtarget->cost.per_tuple * path->rows;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_gather
* Determines and returns the cost of gather path.
*
* 'rel' is the relation to be operated upon
* 'param_info' is the ParamPathInfo if this is a parameterized path, else NULL
* 'rows' may be used to point to a row estimate; if non-NULL, it overrides
* both 'rel' and 'param_info'. This is useful when the path doesn't exactly
* correspond to any particular RelOptInfo.
*/
void
cost_gather(GatherPath *path, PlannerInfo *root,
RelOptInfo *rel, ParamPathInfo *param_info,
double *rows)
{
Cost startup_cost = 0;
Cost run_cost = 0;
/* Mark the path with the correct row estimate */
if (rows)
path->path.rows = *rows;
else if (param_info)
path->path.rows = param_info->ppi_rows;
else
path->path.rows = rel->rows;
startup_cost = path->subpath->startup_cost;
run_cost = path->subpath->total_cost - path->subpath->startup_cost;
/* Parallel setup and communication cost. */
startup_cost += parallel_setup_cost;
run_cost += parallel_tuple_cost * path->path.rows;
path->path.startup_cost = startup_cost;
path->path.total_cost = (startup_cost + run_cost);
}
/*
* cost_gather_merge
* Determines and returns the cost of gather merge path.
*
* GatherMerge merges several pre-sorted input streams, using a heap that at
* any given instant holds the next tuple from each stream. If there are N
* streams, we need about N*log2(N) tuple comparisons to construct the heap at
* startup, and then for each output tuple, about log2(N) comparisons to
* replace the top heap entry with the next tuple from the same stream.
*/
void
cost_gather_merge(GatherMergePath *path, PlannerInfo *root,
RelOptInfo *rel, ParamPathInfo *param_info,
Cost input_startup_cost, Cost input_total_cost,
double *rows)
{
Cost startup_cost = 0;
Cost run_cost = 0;
Cost comparison_cost;
double N;
double logN;
/* Mark the path with the correct row estimate */
if (rows)
path->path.rows = *rows;
else if (param_info)
path->path.rows = param_info->ppi_rows;
else
path->path.rows = rel->rows;
if (!enable_gathermerge)
startup_cost += disable_cost;
/*
* Add one to the number of workers to account for the leader. This might
* be overgenerous since the leader will do less work than other workers
* in typical cases, but we'll go with it for now.
*/
Assert(path->num_workers > 0);
N = (double) path->num_workers + 1;
logN = LOG2(N);
/* Assumed cost per tuple comparison */
comparison_cost = 2.0 * cpu_operator_cost;
/* Heap creation cost */
startup_cost += comparison_cost * N * logN;
/* Per-tuple heap maintenance cost */
run_cost += path->path.rows * comparison_cost * logN;
/* small cost for heap management, like cost_merge_append */
run_cost += cpu_operator_cost * path->path.rows;
/*
* Parallel setup and communication cost. Since Gather Merge, unlike
* Gather, requires us to block until a tuple is available from every
* worker, we bump the IPC cost up a little bit as compared with Gather.
* For lack of a better idea, charge an extra 5%.
*/
startup_cost += parallel_setup_cost;
run_cost += parallel_tuple_cost * path->path.rows * 1.05;
path->path.startup_cost = startup_cost + input_startup_cost;
path->path.total_cost = (startup_cost + run_cost + input_total_cost);
}
/*
* cost_index
* Determines and returns the cost of scanning a relation using an index.
*
* 'path' describes the indexscan under consideration, and is complete
* except for the fields to be set by this routine
* 'loop_count' is the number of repetitions of the indexscan to factor into
* estimates of caching behavior
*
* In addition to rows, startup_cost and total_cost, cost_index() sets the
* path's indextotalcost and indexselectivity fields. These values will be
* needed if the IndexPath is used in a BitmapIndexScan.
*
* NOTE: path->indexquals must contain only clauses usable as index
* restrictions. Any additional quals evaluated as qpquals may reduce the
* number of returned tuples, but they won't reduce the number of tuples
* we have to fetch from the table, so they don't reduce the scan cost.
*/
void
cost_index(IndexPath *path, PlannerInfo *root, double loop_count,
bool partial_path)
{
IndexOptInfo *index = path->indexinfo;
RelOptInfo *baserel = index->rel;
bool indexonly = (path->path.pathtype == T_IndexOnlyScan);
amcostestimate_function amcostestimate;
List *qpquals;
Cost startup_cost = 0;
Cost run_cost = 0;
Cost cpu_run_cost = 0;
Cost indexStartupCost;
Cost indexTotalCost;
Selectivity indexSelectivity;
double indexCorrelation,
csquared;
double spc_seq_page_cost,
spc_random_page_cost;
Cost min_IO_cost,
max_IO_cost;
QualCost qpqual_cost;
Cost cpu_per_tuple;
double tuples_fetched;
double pages_fetched;
double rand_heap_pages;
double index_pages;
/* Should only be applied to base relations */
Assert(IsA(baserel, RelOptInfo) &&
IsA(index, IndexOptInfo));
Assert(baserel->relid > 0);
Assert(baserel->rtekind == RTE_RELATION);
/*
* Mark the path with the correct row estimate, and identify which quals
* will need to be enforced as qpquals. We need not check any quals that
* are implied by the index's predicate, so we can use indrestrictinfo not
* baserestrictinfo as the list of relevant restriction clauses for the
* rel.
*/
if (path->path.param_info)
{
path->path.rows = path->path.param_info->ppi_rows;
/* qpquals come from the rel's restriction clauses and ppi_clauses */
qpquals = list_concat(extract_nonindex_conditions(path->indexinfo->indrestrictinfo,
path->indexclauses),
extract_nonindex_conditions(path->path.param_info->ppi_clauses,
path->indexclauses));
}
else
{
path->path.rows = baserel->rows;
/* qpquals come from just the rel's restriction clauses */
qpquals = extract_nonindex_conditions(path->indexinfo->indrestrictinfo,
path->indexclauses);
}
if (!enable_indexscan)
startup_cost += disable_cost;
/* we don't need to check enable_indexonlyscan; indxpath.c does that */
/*
* Call index-access-method-specific code to estimate the processing cost
* for scanning the index, as well as the selectivity of the index (ie,
* the fraction of main-table tuples we will have to retrieve) and its
* correlation to the main-table tuple order. We need a cast here because
* pathnodes.h uses a weak function type to avoid including amapi.h.
*/
amcostestimate = (amcostestimate_function) index->amcostestimate;
amcostestimate(root, path, loop_count,
&indexStartupCost, &indexTotalCost,
&indexSelectivity, &indexCorrelation,
&index_pages);
/*
* Save amcostestimate's results for possible use in bitmap scan planning.
* We don't bother to save indexStartupCost or indexCorrelation, because a
* bitmap scan doesn't care about either.
*/
path->indextotalcost = indexTotalCost;
path->indexselectivity = indexSelectivity;
/* all costs for touching index itself included here */
startup_cost += indexStartupCost;
run_cost += indexTotalCost - indexStartupCost;
/* estimate number of main-table tuples fetched */
tuples_fetched = clamp_row_est(indexSelectivity * baserel->tuples);
/* fetch estimated page costs for tablespace containing table */
get_tablespace_page_costs(baserel->reltablespace,
&spc_random_page_cost,
&spc_seq_page_cost);
/*----------
* Estimate number of main-table pages fetched, and compute I/O cost.
*
* When the index ordering is uncorrelated with the table ordering,
* we use an approximation proposed by Mackert and Lohman (see
* index_pages_fetched() for details) to compute the number of pages
* fetched, and then charge spc_random_page_cost per page fetched.
*
* When the index ordering is exactly correlated with the table ordering
* (just after a CLUSTER, for example), the number of pages fetched should
* be exactly selectivity * table_size. What's more, all but the first
* will be sequential fetches, not the random fetches that occur in the
* uncorrelated case. So if the number of pages is more than 1, we
* ought to charge
* spc_random_page_cost + (pages_fetched - 1) * spc_seq_page_cost
* For partially-correlated indexes, we ought to charge somewhere between
* these two estimates. We currently interpolate linearly between the
* estimates based on the correlation squared (XXX is that appropriate?).
*
* If it's an index-only scan, then we will not need to fetch any heap
* pages for which the visibility map shows all tuples are visible.
* Hence, reduce the estimated number of heap fetches accordingly.
* We use the measured fraction of the entire heap that is all-visible,
* which might not be particularly relevant to the subset of the heap
* that this query will fetch; but it's not clear how to do better.
*----------
*/
if (loop_count > 1)
{
/*
* For repeated indexscans, the appropriate estimate for the
* uncorrelated case is to scale up the number of tuples fetched in
* the Mackert and Lohman formula by the number of scans, so that we
* estimate the number of pages fetched by all the scans; then
* pro-rate the costs for one scan. In this case we assume all the
* fetches are random accesses.
*/
pages_fetched = index_pages_fetched(tuples_fetched * loop_count,
baserel->pages,
(double) index->pages,
root);
if (indexonly)
pages_fetched = ceil(pages_fetched * (1.0 - baserel->allvisfrac));
rand_heap_pages = pages_fetched;
max_IO_cost = (pages_fetched * spc_random_page_cost) / loop_count;
/*
* In the perfectly correlated case, the number of pages touched by
* each scan is selectivity * table_size, and we can use the Mackert
* and Lohman formula at the page level to estimate how much work is
* saved by caching across scans. We still assume all the fetches are
* random, though, which is an overestimate that's hard to correct for
* without double-counting the cache effects. (But in most cases
* where such a plan is actually interesting, only one page would get
* fetched per scan anyway, so it shouldn't matter much.)
*/
pages_fetched = ceil(indexSelectivity * (double) baserel->pages);
pages_fetched = index_pages_fetched(pages_fetched * loop_count,
baserel->pages,
(double) index->pages,
root);
if (indexonly)
pages_fetched = ceil(pages_fetched * (1.0 - baserel->allvisfrac));
min_IO_cost = (pages_fetched * spc_random_page_cost) / loop_count;
}
else
{
/*
* Normal case: apply the Mackert and Lohman formula, and then
* interpolate between that and the correlation-derived result.
*/
pages_fetched = index_pages_fetched(tuples_fetched,
baserel->pages,
(double) index->pages,
root);
if (indexonly)
pages_fetched = ceil(pages_fetched * (1.0 - baserel->allvisfrac));
rand_heap_pages = pages_fetched;
/* max_IO_cost is for the perfectly uncorrelated case (csquared=0) */
max_IO_cost = pages_fetched * spc_random_page_cost;
/* min_IO_cost is for the perfectly correlated case (csquared=1) */
pages_fetched = ceil(indexSelectivity * (double) baserel->pages);
if (indexonly)
pages_fetched = ceil(pages_fetched * (1.0 - baserel->allvisfrac));
if (pages_fetched > 0)
{
min_IO_cost = spc_random_page_cost;
if (pages_fetched > 1)
min_IO_cost += (pages_fetched - 1) * spc_seq_page_cost;
}
else
min_IO_cost = 0;
}
if (partial_path)
{
/*
* For index only scans compute workers based on number of index pages
* fetched; the number of heap pages we fetch might be so small as to
* effectively rule out parallelism, which we don't want to do.
*/
if (indexonly)
rand_heap_pages = -1;
/*
* Estimate the number of parallel workers required to scan index. Use
* the number of heap pages computed considering heap fetches won't be
* sequential as for parallel scans the pages are accessed in random
* order.
*/
path->path.parallel_workers = compute_parallel_worker(baserel,
rand_heap_pages,
index_pages,
max_parallel_workers_per_gather);
/*
* Fall out if workers can't be assigned for parallel scan, because in
* such a case this path will be rejected. So there is no benefit in
* doing extra computation.
*/
if (path->path.parallel_workers <= 0)
return;
path->path.parallel_aware = true;
}
/*
* Now interpolate based on estimated index order correlation to get total
* disk I/O cost for main table accesses.
*/
csquared = indexCorrelation * indexCorrelation;
run_cost += max_IO_cost + csquared * (min_IO_cost - max_IO_cost);
/*
* Estimate CPU costs per tuple.
*
* What we want here is cpu_tuple_cost plus the evaluation costs of any
* qual clauses that we have to evaluate as qpquals.
*/
cost_qual_eval(&qpqual_cost, qpquals, root);
startup_cost += qpqual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple;
cpu_run_cost += cpu_per_tuple * tuples_fetched;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->path.pathtarget->cost.startup;
cpu_run_cost += path->path.pathtarget->cost.per_tuple * path->path.rows;
/* Adjust costing for parallelism, if used. */
if (path->path.parallel_workers > 0)
{
double parallel_divisor = get_parallel_divisor(&path->path);
path->path.rows = clamp_row_est(path->path.rows / parallel_divisor);
/* The CPU cost is divided among all the workers. */
cpu_run_cost /= parallel_divisor;
}
run_cost += cpu_run_cost;
path->path.startup_cost = startup_cost;
path->path.total_cost = startup_cost + run_cost;
}
/*
* extract_nonindex_conditions
*
* Given a list of quals to be enforced in an indexscan, extract the ones that
* will have to be applied as qpquals (ie, the index machinery won't handle
* them). Here we detect only whether a qual clause is directly redundant
* with some indexclause. If the index path is chosen for use, createplan.c
* will try a bit harder to get rid of redundant qual conditions; specifically
* it will see if quals can be proven to be implied by the indexquals. But
* it does not seem worth the cycles to try to factor that in at this stage,
* since we're only trying to estimate qual eval costs. Otherwise this must
* match the logic in create_indexscan_plan().
*
* qual_clauses, and the result, are lists of RestrictInfos.
* indexclauses is a list of IndexClauses.
*/
static List *
extract_nonindex_conditions(List *qual_clauses, List *indexclauses)
{
List *result = NIL;
ListCell *lc;
foreach(lc, qual_clauses)
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
if (rinfo->pseudoconstant)
continue; /* we may drop pseudoconstants here */
if (is_redundant_with_indexclauses(rinfo, indexclauses))
continue; /* dup or derived from same EquivalenceClass */
/* ... skip the predicate proof attempt createplan.c will try ... */
result = lappend(result, rinfo);
}
return result;
}
/*
* index_pages_fetched
* Estimate the number of pages actually fetched after accounting for
* cache effects.
*
* We use an approximation proposed by Mackert and Lohman, "Index Scans
* Using a Finite LRU Buffer: A Validated I/O Model", ACM Transactions
* on Database Systems, Vol. 14, No. 3, September 1989, Pages 401-424.
* The Mackert and Lohman approximation is that the number of pages
* fetched is
* PF =
* min(2TNs/(2T+Ns), T) when T <= b
* 2TNs/(2T+Ns) when T > b and Ns <= 2Tb/(2T-b)
* b + (Ns - 2Tb/(2T-b))*(T-b)/T when T > b and Ns > 2Tb/(2T-b)
* where
* T = # pages in table
* N = # tuples in table
* s = selectivity = fraction of table to be scanned
* b = # buffer pages available (we include kernel space here)
*
* We assume that effective_cache_size is the total number of buffer pages
* available for the whole query, and pro-rate that space across all the
* tables in the query and the index currently under consideration. (This
* ignores space needed for other indexes used by the query, but since we
* don't know which indexes will get used, we can't estimate that very well;
* and in any case counting all the tables may well be an overestimate, since
* depending on the join plan not all the tables may be scanned concurrently.)
*
* The product Ns is the number of tuples fetched; we pass in that
* product rather than calculating it here. "pages" is the number of pages
* in the object under consideration (either an index or a table).
* "index_pages" is the amount to add to the total table space, which was
* computed for us by make_one_rel.
*
* Caller is expected to have ensured that tuples_fetched is greater than zero
* and rounded to integer (see clamp_row_est). The result will likewise be
* greater than zero and integral.
*/
double
index_pages_fetched(double tuples_fetched, BlockNumber pages,
double index_pages, PlannerInfo *root)
{
double pages_fetched;
double total_pages;
double T,
b;
/* T is # pages in table, but don't allow it to be zero */
T = (pages > 1) ? (double) pages : 1.0;
/* Compute number of pages assumed to be competing for cache space */
total_pages = root->total_table_pages + index_pages;
total_pages = Max(total_pages, 1.0);
Assert(T <= total_pages);
/* b is pro-rated share of effective_cache_size */
b = (double) effective_cache_size * T / total_pages;
/* force it positive and integral */
if (b <= 1.0)
b = 1.0;
else
b = ceil(b);
/* This part is the Mackert and Lohman formula */
if (T <= b)
{
pages_fetched =
(2.0 * T * tuples_fetched) / (2.0 * T + tuples_fetched);
if (pages_fetched >= T)
pages_fetched = T;
else
pages_fetched = ceil(pages_fetched);
}
else
{
double lim;
lim = (2.0 * T * b) / (2.0 * T - b);
if (tuples_fetched <= lim)
{
pages_fetched =
(2.0 * T * tuples_fetched) / (2.0 * T + tuples_fetched);
}
else
{
pages_fetched =
b + (tuples_fetched - lim) * (T - b) / T;
}
pages_fetched = ceil(pages_fetched);
}
return pages_fetched;
}
/*
* get_indexpath_pages
* Determine the total size of the indexes used in a bitmap index path.
*
* Note: if the same index is used more than once in a bitmap tree, we will
* count it multiple times, which perhaps is the wrong thing ... but it's
* not completely clear, and detecting duplicates is difficult, so ignore it
* for now.
*/
static double
get_indexpath_pages(Path *bitmapqual)
{
double result = 0;
ListCell *l;
if (IsA(bitmapqual, BitmapAndPath))
{
BitmapAndPath *apath = (BitmapAndPath *) bitmapqual;
foreach(l, apath->bitmapquals)
{
result += get_indexpath_pages((Path *) lfirst(l));
}
}
else if (IsA(bitmapqual, BitmapOrPath))
{
BitmapOrPath *opath = (BitmapOrPath *) bitmapqual;
foreach(l, opath->bitmapquals)
{
result += get_indexpath_pages((Path *) lfirst(l));
}
}
else if (IsA(bitmapqual, IndexPath))
{
IndexPath *ipath = (IndexPath *) bitmapqual;
result = (double) ipath->indexinfo->pages;
}
else
elog(ERROR, "unrecognized node type: %d", nodeTag(bitmapqual));
return result;
}
/*
* cost_bitmap_heap_scan
* Determines and returns the cost of scanning a relation using a bitmap
* index-then-heap plan.
*
* 'baserel' is the relation to be scanned
* 'param_info' is the ParamPathInfo if this is a parameterized path, else NULL
* 'bitmapqual' is a tree of IndexPaths, BitmapAndPaths, and BitmapOrPaths
* 'loop_count' is the number of repetitions of the indexscan to factor into
* estimates of caching behavior
*
* Note: the component IndexPaths in bitmapqual should have been costed
* using the same loop_count.
*/
void
cost_bitmap_heap_scan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
ParamPathInfo *param_info,
Path *bitmapqual, double loop_count)
{
Cost startup_cost = 0;
Cost run_cost = 0;
Cost indexTotalCost;
QualCost qpqual_cost;
Cost cpu_per_tuple;
Cost cost_per_page;
Cost cpu_run_cost;
double tuples_fetched;
double pages_fetched;
double spc_seq_page_cost,
spc_random_page_cost;
double T;
/* Should only be applied to base relations */
Assert(IsA(baserel, RelOptInfo));
Assert(baserel->relid > 0);
Assert(baserel->rtekind == RTE_RELATION);
/* Mark the path with the correct row estimate */
if (param_info)
path->rows = param_info->ppi_rows;
else
path->rows = baserel->rows;
if (!enable_bitmapscan)
startup_cost += disable_cost;
pages_fetched = compute_bitmap_pages(root, baserel, bitmapqual,
loop_count, &indexTotalCost,
&tuples_fetched);
startup_cost += indexTotalCost;
T = (baserel->pages > 1) ? (double) baserel->pages : 1.0;
/* Fetch estimated page costs for tablespace containing table. */
get_tablespace_page_costs(baserel->reltablespace,
&spc_random_page_cost,
&spc_seq_page_cost);
/*
* For small numbers of pages we should charge spc_random_page_cost
* apiece, while if nearly all the table's pages are being read, it's more
* appropriate to charge spc_seq_page_cost apiece. The effect is
* nonlinear, too. For lack of a better idea, interpolate like this to
* determine the cost per page.
*/
if (pages_fetched >= 2.0)
cost_per_page = spc_random_page_cost -
(spc_random_page_cost - spc_seq_page_cost)
* sqrt(pages_fetched / T);
else
cost_per_page = spc_random_page_cost;
run_cost += pages_fetched * cost_per_page;
/*
* Estimate CPU costs per tuple.
*
* Often the indexquals don't need to be rechecked at each tuple ... but
* not always, especially not if there are enough tuples involved that the
* bitmaps become lossy. For the moment, just assume they will be
* rechecked always. This means we charge the full freight for all the
* scan clauses.
*/
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
startup_cost += qpqual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple;
cpu_run_cost = cpu_per_tuple * tuples_fetched;
/* Adjust costing for parallelism, if used. */
if (path->parallel_workers > 0)
{
double parallel_divisor = get_parallel_divisor(path);
/* The CPU cost is divided among all the workers. */
cpu_run_cost /= parallel_divisor;
path->rows = clamp_row_est(path->rows / parallel_divisor);
}
run_cost += cpu_run_cost;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->pathtarget->cost.startup;
run_cost += path->pathtarget->cost.per_tuple * path->rows;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_bitmap_tree_node
* Extract cost and selectivity from a bitmap tree node (index/and/or)
*/
void
cost_bitmap_tree_node(Path *path, Cost *cost, Selectivity *selec)
{
if (IsA(path, IndexPath))
{
*cost = ((IndexPath *) path)->indextotalcost;
*selec = ((IndexPath *) path)->indexselectivity;
/*
* Charge a small amount per retrieved tuple to reflect the costs of
* manipulating the bitmap. This is mostly to make sure that a bitmap
* scan doesn't look to be the same cost as an indexscan to retrieve a
* single tuple.
*/
*cost += 0.1 * cpu_operator_cost * path->rows;
}
else if (IsA(path, BitmapAndPath))
{
*cost = path->total_cost;
*selec = ((BitmapAndPath *) path)->bitmapselectivity;
}
else if (IsA(path, BitmapOrPath))
{
*cost = path->total_cost;
*selec = ((BitmapOrPath *) path)->bitmapselectivity;
}
else
{
elog(ERROR, "unrecognized node type: %d", nodeTag(path));
*cost = *selec = 0; /* keep compiler quiet */
}
}
/*
* cost_bitmap_and_node
* Estimate the cost of a BitmapAnd node
*
* Note that this considers only the costs of index scanning and bitmap
* creation, not the eventual heap access. In that sense the object isn't
* truly a Path, but it has enough path-like properties (costs in particular)
* to warrant treating it as one. We don't bother to set the path rows field,
* however.
*/
void
cost_bitmap_and_node(BitmapAndPath *path, PlannerInfo *root)
{
Cost totalCost;
Selectivity selec;
ListCell *l;
/*
* We estimate AND selectivity on the assumption that the inputs are
* independent. This is probably often wrong, but we don't have the info
* to do better.
*
* The runtime cost of the BitmapAnd itself is estimated at 100x
* cpu_operator_cost for each tbm_intersect needed. Probably too small,
* definitely too simplistic?
*/
totalCost = 0.0;
selec = 1.0;
foreach(l, path->bitmapquals)
{
Path *subpath = (Path *) lfirst(l);
Cost subCost;
Selectivity subselec;
cost_bitmap_tree_node(subpath, &subCost, &subselec);
selec *= subselec;
totalCost += subCost;
if (l != list_head(path->bitmapquals))
totalCost += 100.0 * cpu_operator_cost;
}
path->bitmapselectivity = selec;
path->path.rows = 0; /* per above, not used */
path->path.startup_cost = totalCost;
path->path.total_cost = totalCost;
}
/*
* cost_bitmap_or_node
* Estimate the cost of a BitmapOr node
*
* See comments for cost_bitmap_and_node.
*/
void
cost_bitmap_or_node(BitmapOrPath *path, PlannerInfo *root)
{
Cost totalCost;
Selectivity selec;
ListCell *l;
/*
* We estimate OR selectivity on the assumption that the inputs are
* non-overlapping, since that's often the case in "x IN (list)" type
* situations. Of course, we clamp to 1.0 at the end.
*
* The runtime cost of the BitmapOr itself is estimated at 100x
* cpu_operator_cost for each tbm_union needed. Probably too small,
* definitely too simplistic? We are aware that the tbm_unions are
* optimized out when the inputs are BitmapIndexScans.
*/
totalCost = 0.0;
selec = 0.0;
foreach(l, path->bitmapquals)
{
Path *subpath = (Path *) lfirst(l);
Cost subCost;
Selectivity subselec;
cost_bitmap_tree_node(subpath, &subCost, &subselec);
selec += subselec;
totalCost += subCost;
if (l != list_head(path->bitmapquals) &&
!IsA(subpath, IndexPath))
totalCost += 100.0 * cpu_operator_cost;
}
path->bitmapselectivity = Min(selec, 1.0);
path->path.rows = 0; /* per above, not used */
path->path.startup_cost = totalCost;
path->path.total_cost = totalCost;
}
/*
* cost_tidscan
* Determines and returns the cost of scanning a relation using TIDs.
*
* 'baserel' is the relation to be scanned
* 'tidquals' is the list of TID-checkable quals
* 'param_info' is the ParamPathInfo if this is a parameterized path, else NULL
*/
void
cost_tidscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, List *tidquals, ParamPathInfo *param_info)
{
Cost startup_cost = 0;
Cost run_cost = 0;
bool isCurrentOf = false;
QualCost qpqual_cost;
Cost cpu_per_tuple;
QualCost tid_qual_cost;
int ntuples;
ListCell *l;
double spc_random_page_cost;
/* Should only be applied to base relations */
Assert(baserel->relid > 0);
Assert(baserel->rtekind == RTE_RELATION);
/* Mark the path with the correct row estimate */
if (param_info)
path->rows = param_info->ppi_rows;
else
path->rows = baserel->rows;
/* Count how many tuples we expect to retrieve */
ntuples = 0;
foreach(l, tidquals)
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, l);
Expr *qual = rinfo->clause;
if (IsA(qual, ScalarArrayOpExpr))
{
/* Each element of the array yields 1 tuple */
ScalarArrayOpExpr *saop = (ScalarArrayOpExpr *) qual;
Node *arraynode = (Node *) lsecond(saop->args);
ntuples += estimate_array_length(arraynode);
}
else if (IsA(qual, CurrentOfExpr))
{
/* CURRENT OF yields 1 tuple */
isCurrentOf = true;
ntuples++;
}
else
{
/* It's just CTID = something, count 1 tuple */
ntuples++;
}
}
/*
* We must force TID scan for WHERE CURRENT OF, because only nodeTidscan.c
* understands how to do it correctly. Therefore, honor enable_tidscan
* only when CURRENT OF isn't present. Also note that cost_qual_eval
* counts a CurrentOfExpr as having startup cost disable_cost, which we
* subtract off here; that's to prevent other plan types such as seqscan
* from winning.
*/
if (isCurrentOf)
{
Assert(baserel->baserestrictcost.startup >= disable_cost);
startup_cost -= disable_cost;
}
else if (!enable_tidscan)
startup_cost += disable_cost;
/*
* The TID qual expressions will be computed once, any other baserestrict
* quals once per retrieved tuple.
*/
cost_qual_eval(&tid_qual_cost, tidquals, root);
/* fetch estimated page cost for tablespace containing table */
get_tablespace_page_costs(baserel->reltablespace,
&spc_random_page_cost,
NULL);
/* disk costs --- assume each tuple on a different page */
run_cost += spc_random_page_cost * ntuples;
/* Add scanning CPU costs */
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
/* XXX currently we assume TID quals are a subset of qpquals */
startup_cost += qpqual_cost.startup + tid_qual_cost.per_tuple;
cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple -
tid_qual_cost.per_tuple;
run_cost += cpu_per_tuple * ntuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->pathtarget->cost.startup;
run_cost += path->pathtarget->cost.per_tuple * path->rows;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_subqueryscan
* Determines and returns the cost of scanning a subquery RTE.
*
* 'baserel' is the relation to be scanned
* 'param_info' is the ParamPathInfo if this is a parameterized path, else NULL
*/
void
cost_subqueryscan(SubqueryScanPath *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info)
{
Cost startup_cost;
Cost run_cost;
QualCost qpqual_cost;
Cost cpu_per_tuple;
/* Should only be applied to base relations that are subqueries */
Assert(baserel->relid > 0);
Assert(baserel->rtekind == RTE_SUBQUERY);
/* Mark the path with the correct row estimate */
if (param_info)
path->path.rows = param_info->ppi_rows;
else
path->path.rows = baserel->rows;
/*
* Cost of path is cost of evaluating the subplan, plus cost of evaluating
* any restriction clauses and tlist that will be attached to the
* SubqueryScan node, plus cpu_tuple_cost to account for selection and
* projection overhead.
*/
path->path.startup_cost = path->subpath->startup_cost;
path->path.total_cost = path->subpath->total_cost;
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
startup_cost = qpqual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple;
run_cost = cpu_per_tuple * baserel->tuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->path.pathtarget->cost.startup;
run_cost += path->path.pathtarget->cost.per_tuple * path->path.rows;
path->path.startup_cost += startup_cost;
path->path.total_cost += startup_cost + run_cost;
}
/*
* cost_functionscan
* Determines and returns the cost of scanning a function RTE.
*
* 'baserel' is the relation to be scanned
* 'param_info' is the ParamPathInfo if this is a parameterized path, else NULL
*/
void
cost_functionscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info)
{
Cost startup_cost = 0;
Cost run_cost = 0;
QualCost qpqual_cost;
Cost cpu_per_tuple;
RangeTblEntry *rte;
QualCost exprcost;
/* Should only be applied to base relations that are functions */
Assert(baserel->relid > 0);
rte = planner_rt_fetch(baserel->relid, root);
Assert(rte->rtekind == RTE_FUNCTION);
/* Mark the path with the correct row estimate */
if (param_info)
path->rows = param_info->ppi_rows;
else
path->rows = baserel->rows;
/*
* Estimate costs of executing the function expression(s).
*
* Currently, nodeFunctionscan.c always executes the functions to
* completion before returning any rows, and caches the results in a
* tuplestore. So the function eval cost is all startup cost, and per-row
* costs are minimal.
*
* XXX in principle we ought to charge tuplestore spill costs if the
* number of rows is large. However, given how phony our rowcount
* estimates for functions tend to be, there's not a lot of point in that
* refinement right now.
*/
cost_qual_eval_node(&exprcost, (Node *) rte->functions, root);
startup_cost += exprcost.startup + exprcost.per_tuple;
/* Add scanning CPU costs */
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
startup_cost += qpqual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple;
run_cost += cpu_per_tuple * baserel->tuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->pathtarget->cost.startup;
run_cost += path->pathtarget->cost.per_tuple * path->rows;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_tablefuncscan
* Determines and returns the cost of scanning a table function.
*
* 'baserel' is the relation to be scanned
* 'param_info' is the ParamPathInfo if this is a parameterized path, else NULL
*/
void
cost_tablefuncscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info)
{
Cost startup_cost = 0;
Cost run_cost = 0;
QualCost qpqual_cost;
Cost cpu_per_tuple;
RangeTblEntry *rte;
QualCost exprcost;
/* Should only be applied to base relations that are functions */
Assert(baserel->relid > 0);
rte = planner_rt_fetch(baserel->relid, root);
Assert(rte->rtekind == RTE_TABLEFUNC);
/* Mark the path with the correct row estimate */
if (param_info)
path->rows = param_info->ppi_rows;
else
path->rows = baserel->rows;
/*
* Estimate costs of executing the table func expression(s).
*
* XXX in principle we ought to charge tuplestore spill costs if the
* number of rows is large. However, given how phony our rowcount
* estimates for tablefuncs tend to be, there's not a lot of point in that
* refinement right now.
*/
cost_qual_eval_node(&exprcost, (Node *) rte->tablefunc, root);
startup_cost += exprcost.startup + exprcost.per_tuple;
/* Add scanning CPU costs */
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
startup_cost += qpqual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple;
run_cost += cpu_per_tuple * baserel->tuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->pathtarget->cost.startup;
run_cost += path->pathtarget->cost.per_tuple * path->rows;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_valuesscan
* Determines and returns the cost of scanning a VALUES RTE.
*
* 'baserel' is the relation to be scanned
* 'param_info' is the ParamPathInfo if this is a parameterized path, else NULL
*/
void
cost_valuesscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info)
{
Cost startup_cost = 0;
Cost run_cost = 0;
QualCost qpqual_cost;
Cost cpu_per_tuple;
/* Should only be applied to base relations that are values lists */
Assert(baserel->relid > 0);
Assert(baserel->rtekind == RTE_VALUES);
/* Mark the path with the correct row estimate */
if (param_info)
path->rows = param_info->ppi_rows;
else
path->rows = baserel->rows;
/*
* For now, estimate list evaluation cost at one operator eval per list
* (probably pretty bogus, but is it worth being smarter?)
*/
cpu_per_tuple = cpu_operator_cost;
/* Add scanning CPU costs */
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
startup_cost += qpqual_cost.startup;
cpu_per_tuple += cpu_tuple_cost + qpqual_cost.per_tuple;
run_cost += cpu_per_tuple * baserel->tuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->pathtarget->cost.startup;
run_cost += path->pathtarget->cost.per_tuple * path->rows;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_ctescan
* Determines and returns the cost of scanning a CTE RTE.
*
* Note: this is used for both self-reference and regular CTEs; the
* possible cost differences are below the threshold of what we could
* estimate accurately anyway. Note that the costs of evaluating the
* referenced CTE query are added into the final plan as initplan costs,
* and should NOT be counted here.
*/
void
cost_ctescan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info)
{
Cost startup_cost = 0;
Cost run_cost = 0;
QualCost qpqual_cost;
Cost cpu_per_tuple;
/* Should only be applied to base relations that are CTEs */
Assert(baserel->relid > 0);
Assert(baserel->rtekind == RTE_CTE);
/* Mark the path with the correct row estimate */
if (param_info)
path->rows = param_info->ppi_rows;
else
path->rows = baserel->rows;
/* Charge one CPU tuple cost per row for tuplestore manipulation */
cpu_per_tuple = cpu_tuple_cost;
/* Add scanning CPU costs */
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
startup_cost += qpqual_cost.startup;
cpu_per_tuple += cpu_tuple_cost + qpqual_cost.per_tuple;
run_cost += cpu_per_tuple * baserel->tuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->pathtarget->cost.startup;
run_cost += path->pathtarget->cost.per_tuple * path->rows;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_namedtuplestorescan
* Determines and returns the cost of scanning a named tuplestore.
*/
void
cost_namedtuplestorescan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info)
{
Cost startup_cost = 0;
Cost run_cost = 0;
QualCost qpqual_cost;
Cost cpu_per_tuple;
/* Should only be applied to base relations that are Tuplestores */
Assert(baserel->relid > 0);
Assert(baserel->rtekind == RTE_NAMEDTUPLESTORE);
/* Mark the path with the correct row estimate */
if (param_info)
path->rows = param_info->ppi_rows;
else
path->rows = baserel->rows;
/* Charge one CPU tuple cost per row for tuplestore manipulation */
cpu_per_tuple = cpu_tuple_cost;
/* Add scanning CPU costs */
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
startup_cost += qpqual_cost.startup;
cpu_per_tuple += cpu_tuple_cost + qpqual_cost.per_tuple;
run_cost += cpu_per_tuple * baserel->tuples;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_resultscan
* Determines and returns the cost of scanning an RTE_RESULT relation.
*/
void
cost_resultscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info)
{
Cost startup_cost = 0;
Cost run_cost = 0;
QualCost qpqual_cost;
Cost cpu_per_tuple;
/* Should only be applied to RTE_RESULT base relations */
Assert(baserel->relid > 0);
Assert(baserel->rtekind == RTE_RESULT);
/* Mark the path with the correct row estimate */
if (param_info)
path->rows = param_info->ppi_rows;
else
path->rows = baserel->rows;
/* We charge qual cost plus cpu_tuple_cost */
get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
startup_cost += qpqual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple;
run_cost += cpu_per_tuple * baserel->tuples;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_recursive_union
* Determines and returns the cost of performing a recursive union,
* and also the estimated output size.
*
* We are given Paths for the nonrecursive and recursive terms.
*/
void
cost_recursive_union(Path *runion, Path *nrterm, Path *rterm)
{
Cost startup_cost;
Cost total_cost;
double total_rows;
/* We probably have decent estimates for the non-recursive term */
startup_cost = nrterm->startup_cost;
total_cost = nrterm->total_cost;
total_rows = nrterm->rows;
/*
* We arbitrarily assume that about 10 recursive iterations will be
* needed, and that we've managed to get a good fix on the cost and output
* size of each one of them. These are mighty shaky assumptions but it's
* hard to see how to do better.
*/
total_cost += 10 * rterm->total_cost;
total_rows += 10 * rterm->rows;
/*
* Also charge cpu_tuple_cost per row to account for the costs of
* manipulating the tuplestores. (We don't worry about possible
* spill-to-disk costs.)
*/
total_cost += cpu_tuple_cost * total_rows;
runion->startup_cost = startup_cost;
runion->total_cost = total_cost;
runion->rows = total_rows;
runion->pathtarget->width = Max(nrterm->pathtarget->width,
rterm->pathtarget->width);
}
/*
* cost_tuplesort
* Determines and returns the cost of sorting a relation using tuplesort,
* not including the cost of reading the input data.
*
* If the total volume of data to sort is less than sort_mem, we will do
* an in-memory sort, which requires no I/O and about t*log2(t) tuple
* comparisons for t tuples.
*
* If the total volume exceeds sort_mem, we switch to a tape-style merge
* algorithm. There will still be about t*log2(t) tuple comparisons in
* total, but we will also need to write and read each tuple once per
* merge pass. We expect about ceil(logM(r)) merge passes where r is the
* number of initial runs formed and M is the merge order used by tuplesort.c.
* Since the average initial run should be about sort_mem, we have
* disk traffic = 2 * relsize * ceil(logM(p / sort_mem))
* cpu = comparison_cost * t * log2(t)
*
* If the sort is bounded (i.e., only the first k result tuples are needed)
* and k tuples can fit into sort_mem, we use a heap method that keeps only
* k tuples in the heap; this will require about t*log2(k) tuple comparisons.
*
* The disk traffic is assumed to be 3/4ths sequential and 1/4th random
* accesses (XXX can't we refine that guess?)
*
* By default, we charge two operator evals per tuple comparison, which should
* be in the right ballpark in most cases. The caller can tweak this by
* specifying nonzero comparison_cost; typically that's used for any extra
* work that has to be done to prepare the inputs to the comparison operators.
*
* 'tuples' is the number of tuples in the relation
* 'width' is the average tuple width in bytes
* 'comparison_cost' is the extra cost per comparison, if any
* 'sort_mem' is the number of kilobytes of work memory allowed for the sort
* 'limit_tuples' is the bound on the number of output tuples; -1 if no bound
*/
static void
cost_tuplesort(Cost *startup_cost, Cost *run_cost,
double tuples, int width,
Cost comparison_cost, int sort_mem,
double limit_tuples)
{
double input_bytes = relation_byte_size(tuples, width);
double output_bytes;
double output_tuples;
long sort_mem_bytes = sort_mem * 1024L;
/*
* We want to be sure the cost of a sort is never estimated as zero, even
* if passed-in tuple count is zero. Besides, mustn't do log(0)...
*/
if (tuples < 2.0)
tuples = 2.0;
/* Include the default cost-per-comparison */
comparison_cost += 2.0 * cpu_operator_cost;
/* Do we have a useful LIMIT? */
if (limit_tuples > 0 && limit_tuples < tuples)
{
output_tuples = limit_tuples;
output_bytes = relation_byte_size(output_tuples, width);
}
else
{
output_tuples = tuples;
output_bytes = input_bytes;
}
if (output_bytes > sort_mem_bytes)
{
/*
* We'll have to use a disk-based sort of all the tuples
*/
double npages = ceil(input_bytes / BLCKSZ);
double nruns = input_bytes / sort_mem_bytes;
double mergeorder = tuplesort_merge_order(sort_mem_bytes);
double log_runs;
double npageaccesses;
/*
* CPU costs
*
* Assume about N log2 N comparisons
*/
*startup_cost = comparison_cost * tuples * LOG2(tuples);
/* Disk costs */
/* Compute logM(r) as log(r) / log(M) */
if (nruns > mergeorder)
log_runs = ceil(log(nruns) / log(mergeorder));
else
log_runs = 1.0;
npageaccesses = 2.0 * npages * log_runs;
/* Assume 3/4ths of accesses are sequential, 1/4th are not */
*startup_cost += npageaccesses *
(seq_page_cost * 0.75 + random_page_cost * 0.25);
}
else if (tuples > 2 * output_tuples || input_bytes > sort_mem_bytes)
{
/*
* We'll use a bounded heap-sort keeping just K tuples in memory, for
* a total number of tuple comparisons of N log2 K; but the constant
* factor is a bit higher than for quicksort. Tweak it so that the
* cost curve is continuous at the crossover point.
*/
*startup_cost = comparison_cost * tuples * LOG2(2.0 * output_tuples);
}
else
{
/* We'll use plain quicksort on all the input tuples */
*startup_cost = comparison_cost * tuples * LOG2(tuples);
}
/*
* Also charge a small amount (arbitrarily set equal to operator cost) per
* extracted tuple. We don't charge cpu_tuple_cost because a Sort node
* doesn't do qual-checking or projection, so it has less overhead than
* most plan nodes. Note it's correct to use tuples not output_tuples
* here --- the upper LIMIT will pro-rate the run cost so we'd be double
* counting the LIMIT otherwise.
*/
*run_cost = cpu_operator_cost * tuples;
}
/*
* cost_incremental_sort
* Determines and returns the cost of sorting a relation incrementally, when
* the input path is presorted by a prefix of the pathkeys.
*
* 'presorted_keys' is the number of leading pathkeys by which the input path
* is sorted.
*
* We estimate the number of groups into which the relation is divided by the
* leading pathkeys, and then calculate the cost of sorting a single group
* with tuplesort using cost_tuplesort().
*/
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)
{
Cost startup_cost = 0,
run_cost = 0,
input_run_cost = input_total_cost - input_startup_cost;
double group_tuples,
input_groups;
Cost group_startup_cost,
group_run_cost,
group_input_run_cost;
List *presortedExprs = NIL;
ListCell *l;
int i = 0;
bool unknown_varno = false;
Assert(presorted_keys != 0);
/*
* We want to be sure the cost of a sort is never estimated as zero, even
* if passed-in tuple count is zero. Besides, mustn't do log(0)...
*/
if (input_tuples < 2.0)
input_tuples = 2.0;
/* Default estimate of number of groups, capped to one group per row. */
input_groups = Min(input_tuples, DEFAULT_NUM_DISTINCT);
/*
* Extract presorted keys as list of expressions.
*
* We need to be careful about Vars containing "varno 0" which might have
* been introduced by generate_append_tlist, which would confuse
* estimate_num_groups (in fact it'd fail for such expressions). See
* recurse_set_operations which has to deal with the same issue.
*
* Unlike recurse_set_operations we can't access the original target list
* here, and even if we could it's not very clear how useful would that be
* for a set operation combining multiple tables. So we simply detect if
* there are any expressions with "varno 0" and use the default
* DEFAULT_NUM_DISTINCT in that case.
*
* We might also use either 1.0 (a single group) or input_tuples (each row
* being a separate group), pretty much the worst and best case for
* incremental sort. But those are extreme cases and using something in
* between seems reasonable. Furthermore, generate_append_tlist is used
* for set operations, which are likely to produce mostly unique output
* anyway - from that standpoint the DEFAULT_NUM_DISTINCT is defensive
* while maintaining lower startup cost.
*/
foreach(l, pathkeys)
{
PathKey *key = (PathKey *) lfirst(l);
EquivalenceMember *member = (EquivalenceMember *)
linitial(key->pk_eclass->ec_members);
/*
* Check if the expression contains Var with "varno 0" so that we
* don't call estimate_num_groups in that case.
*/
if (bms_is_member(0, pull_varnos((Node *) member->em_expr)))
{
unknown_varno = true;
break;
}
/* expression not containing any Vars with "varno 0" */
presortedExprs = lappend(presortedExprs, member->em_expr);
i++;
if (i >= presorted_keys)
break;
}
/* Estimate number of groups with equal presorted keys. */
if (!unknown_varno)
input_groups = estimate_num_groups(root, presortedExprs, input_tuples, NULL);
group_tuples = input_tuples / input_groups;
group_input_run_cost = input_run_cost / input_groups;
/*
* Estimate average cost of sorting of one group where presorted keys are
* equal. Incremental sort is sensitive to distribution of tuples to the
* groups, where we're relying on quite rough assumptions. Thus, we're
* pessimistic about incremental sort performance and increase its average
* group size by half.
*/
cost_tuplesort(&group_startup_cost, &group_run_cost,
1.5 * group_tuples, width, comparison_cost, sort_mem,
limit_tuples);
/*
* Startup cost of incremental sort is the startup cost of its first group
* plus the cost of its input.
*/
startup_cost += group_startup_cost
+ input_startup_cost + group_input_run_cost;
/*
* After we started producing tuples from the first group, the cost of
* producing all the tuples is given by the cost to finish processing this
* group, plus the total cost to process the remaining groups, plus the
* remaining cost of input.
*/
run_cost += group_run_cost
+ (group_run_cost + group_startup_cost) * (input_groups - 1)
+ group_input_run_cost * (input_groups - 1);
/*
* Incremental sort adds some overhead by itself. Firstly, it has to
* detect the sort groups. This is roughly equal to one extra copy and
* comparison per tuple. Secondly, it has to reset the tuplesort context
* for every group.
*/
run_cost += (cpu_tuple_cost + comparison_cost) * input_tuples;
run_cost += 2.0 * cpu_tuple_cost * input_groups;
path->rows = input_tuples;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_sort
* Determines and returns the cost of sorting a relation, including
* the cost of reading the input data.
*
* NOTE: some callers currently pass NIL for pathkeys because they
* can't conveniently supply the sort keys. Since this routine doesn't
* currently do anything with pathkeys anyway, that doesn't matter...
* but if it ever does, it should react gracefully to lack of key data.
* (Actually, the thing we'd most likely be interested in is just the number
* of sort keys, which all callers *could* supply.)
*/
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)
{
Cost startup_cost;
Cost run_cost;
cost_tuplesort(&startup_cost, &run_cost,
tuples, width,
comparison_cost, sort_mem,
limit_tuples);
if (!enable_sort)
startup_cost += disable_cost;
startup_cost += input_cost;
path->rows = tuples;
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* append_nonpartial_cost
* Estimate the cost of the non-partial paths in a Parallel Append.
* The non-partial paths are assumed to be the first "numpaths" paths
* from the subpaths list, and to be in order of decreasing cost.
*/
static Cost
append_nonpartial_cost(List *subpaths, int numpaths, int parallel_workers)
{
Cost *costarr;
int arrlen;
ListCell *l;
ListCell *cell;
int i;
int path_index;
int min_index;
int max_index;
if (numpaths == 0)
return 0;
/*
* Array length is number of workers or number of relevant paths,
* whichever is less.
*/
arrlen = Min(parallel_workers, numpaths);
costarr = (Cost *) palloc(sizeof(Cost) * arrlen);
/* The first few paths will each be claimed by a different worker. */
path_index = 0;
foreach(cell, subpaths)
{
Path *subpath = (Path *) lfirst(cell);
if (path_index == arrlen)
break;
costarr[path_index++] = subpath->total_cost;
}
/*
* Since subpaths are sorted by decreasing cost, the last one will have
* the minimum cost.
*/
min_index = arrlen - 1;
/*
* For each of the remaining subpaths, add its cost to the array element
* with minimum cost.
*/
for_each_cell(l, subpaths, cell)
{
Path *subpath = (Path *) lfirst(l);
int i;
/* Consider only the non-partial paths */
if (path_index++ == numpaths)
break;
costarr[min_index] += subpath->total_cost;
/* Update the new min cost array index */
for (min_index = i = 0; i < arrlen; i++)
{
if (costarr[i] < costarr[min_index])
min_index = i;
}
}
/* Return the highest cost from the array */
for (max_index = i = 0; i < arrlen; i++)
{
if (costarr[i] > costarr[max_index])
max_index = i;
}
return costarr[max_index];
}
/*
* cost_append
* Determines and returns the cost of an Append node.
*/
void
cost_append(AppendPath *apath)
{
ListCell *l;
apath->path.startup_cost = 0;
apath->path.total_cost = 0;
apath->path.rows = 0;
if (apath->subpaths == NIL)
return;
if (!apath->path.parallel_aware)
{
List *pathkeys = apath->path.pathkeys;
if (pathkeys == NIL)
{
Path *subpath = (Path *) linitial(apath->subpaths);
/*
* For an unordered, non-parallel-aware Append we take the startup
* cost as the startup cost of the first subpath.
*/
apath->path.startup_cost = subpath->startup_cost;
/* Compute rows and costs as sums of subplan rows and costs. */
foreach(l, apath->subpaths)
{
Path *subpath = (Path *) lfirst(l);
apath->path.rows += subpath->rows;
apath->path.total_cost += subpath->total_cost;
}
}
else
{
/*
* For an ordered, non-parallel-aware Append we take the startup
* cost as the sum of the subpath startup costs. This ensures
* that we don't underestimate the startup cost when a query's
* LIMIT is such that several of the children have to be run to
* satisfy it. This might be overkill --- another plausible hack
* would be to take the Append's startup cost as the maximum of
* the child startup costs. But we don't want to risk believing
* that an ORDER BY LIMIT query can be satisfied at small cost
* when the first child has small startup cost but later ones
* don't. (If we had the ability to deal with nonlinear cost
* interpolation for partial retrievals, we would not need to be
* so conservative about this.)
*
* This case is also different from the above in that we have to
* account for possibly injecting sorts into subpaths that aren't
* natively ordered.
*/
foreach(l, apath->subpaths)
{
Path *subpath = (Path *) lfirst(l);
Path sort_path; /* dummy for result of cost_sort */
if (!pathkeys_contained_in(pathkeys, subpath->pathkeys))
{
/*
* We'll need to insert a Sort node, so include costs for
* that. We can use the parent's LIMIT if any, since we
* certainly won't pull more than that many tuples from
* any child.
*/
cost_sort(&sort_path,
NULL, /* doesn't currently need root */
pathkeys,
subpath->total_cost,
subpath->rows,
subpath->pathtarget->width,
0.0,
work_mem,
apath->limit_tuples);
subpath = &sort_path;
}
apath->path.rows += subpath->rows;
apath->path.startup_cost += subpath->startup_cost;
apath->path.total_cost += subpath->total_cost;
}
}
}
else /* parallel-aware */
{
int i = 0;
double parallel_divisor = get_parallel_divisor(&apath->path);
/* Parallel-aware Append never produces ordered output. */
Assert(apath->path.pathkeys == NIL);
/* Calculate startup cost. */
foreach(l, apath->subpaths)
{
Path *subpath = (Path *) lfirst(l);
/*
* Append will start returning tuples when the child node having
* lowest startup cost is done setting up. We consider only the
* first few subplans that immediately get a worker assigned.
*/
if (i == 0)
apath->path.startup_cost = subpath->startup_cost;
else if (i < apath->path.parallel_workers)
apath->path.startup_cost = Min(apath->path.startup_cost,
subpath->startup_cost);
/*
* Apply parallel divisor to subpaths. Scale the number of rows
* for each partial subpath based on the ratio of the parallel
* divisor originally used for the subpath to the one we adopted.
* Also add the cost of partial paths to the total cost, but
* ignore non-partial paths for now.
*/
if (i < apath->first_partial_path)
apath->path.rows += subpath->rows / parallel_divisor;
else
{
double subpath_parallel_divisor;
subpath_parallel_divisor = get_parallel_divisor(subpath);
apath->path.rows += subpath->rows * (subpath_parallel_divisor /
parallel_divisor);
apath->path.total_cost += subpath->total_cost;
}
apath->path.rows = clamp_row_est(apath->path.rows);
i++;
}
/* Add cost for non-partial subpaths. */
apath->path.total_cost +=
append_nonpartial_cost(apath->subpaths,
apath->first_partial_path,
apath->path.parallel_workers);
}
/*
* Although Append does not do any selection or projection, it's not free;
* add a small per-tuple overhead.
*/
apath->path.total_cost +=
cpu_tuple_cost * APPEND_CPU_COST_MULTIPLIER * apath->path.rows;
}
/*
* cost_merge_append
* Determines and returns the cost of a MergeAppend node.
*
* MergeAppend merges several pre-sorted input streams, using a heap that
* at any given instant holds the next tuple from each stream. If there
* are N streams, we need about N*log2(N) tuple comparisons to construct
* the heap at startup, and then for each output tuple, about log2(N)
* comparisons to replace the top entry.
*
* (The effective value of N will drop once some of the input streams are
* exhausted, but it seems unlikely to be worth trying to account for that.)
*
* The heap is never spilled to disk, since we assume N is not very large.
* So this is much simpler than cost_sort.
*
* As in cost_sort, we charge two operator evals per tuple comparison.
*
* 'pathkeys' is a list of sort keys
* 'n_streams' is the number of input streams
* 'input_startup_cost' is the sum of the input streams' startup costs
* 'input_total_cost' is the sum of the input streams' total costs
* 'tuples' is the number of tuples in all the streams
*/
void
cost_merge_append(Path *path, PlannerInfo *root,
List *pathkeys, int n_streams,
Cost input_startup_cost, Cost input_total_cost,
double tuples)
{
Cost startup_cost = 0;
Cost run_cost = 0;
Cost comparison_cost;
double N;
double logN;
/*
* Avoid log(0)...
*/
N = (n_streams < 2) ? 2.0 : (double) n_streams;
logN = LOG2(N);
/* Assumed cost per tuple comparison */
comparison_cost = 2.0 * cpu_operator_cost;
/* Heap creation cost */
startup_cost += comparison_cost * N * logN;
/* Per-tuple heap maintenance cost */
run_cost += tuples * comparison_cost * logN;
/*
* Although MergeAppend does not do any selection or projection, it's not
* free; add a small per-tuple overhead.
*/
run_cost += cpu_tuple_cost * APPEND_CPU_COST_MULTIPLIER * tuples;
path->startup_cost = startup_cost + input_startup_cost;
path->total_cost = startup_cost + run_cost + input_total_cost;
}
/*
* cost_material
* Determines and returns the cost of materializing a relation, including
* the cost of reading the input data.
*
* If the total volume of data to materialize exceeds work_mem, we will need
* to write it to disk, so the cost is much higher in that case.
*
* Note that here we are estimating the costs for the first scan of the
* relation, so the materialization is all overhead --- any savings will
* occur only on rescan, which is estimated in cost_rescan.
*/
void
cost_material(Path *path,
Cost input_startup_cost, Cost input_total_cost,
double tuples, int width)
{
Cost startup_cost = input_startup_cost;
Cost run_cost = input_total_cost - input_startup_cost;
double nbytes = relation_byte_size(tuples, width);
long work_mem_bytes = work_mem * 1024L;
path->rows = tuples;
/*
* Whether spilling or not, charge 2x cpu_operator_cost per tuple to
* reflect bookkeeping overhead. (This rate must be more than what
* cost_rescan charges for materialize, ie, cpu_operator_cost per tuple;
* if it is exactly the same then there will be a cost tie between
* nestloop with A outer, materialized B inner and nestloop with B outer,
* materialized A inner. The extra cost ensures we'll prefer
* materializing the smaller rel.) Note that this is normally a good deal
* less than cpu_tuple_cost; which is OK because a Material plan node
* doesn't do qual-checking or projection, so it's got less overhead than
* most plan nodes.
*/
run_cost += 2 * cpu_operator_cost * tuples;
/*
* If we will spill to disk, charge at the rate of seq_page_cost per page.
* This cost is assumed to be evenly spread through the plan run phase,
* which isn't exactly accurate but our cost model doesn't allow for
* nonuniform costs within the run phase.
*/
if (nbytes > work_mem_bytes)
{
double npages = ceil(nbytes / BLCKSZ);
run_cost += seq_page_cost * npages;
}
path->startup_cost = startup_cost;
path->total_cost = startup_cost + run_cost;
}
/*
* cost_agg
* Determines and returns the cost of performing an Agg plan node,
* including the cost of its input.
*
* aggcosts can be NULL when there are no actual aggregate functions (i.e.,
* we are using a hashed Agg node just to do grouping).
*
* Note: when aggstrategy == AGG_SORTED, caller must ensure that input costs
* are for appropriately-sorted input.
*/
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)
{
double output_tuples;
Cost startup_cost;
Cost total_cost;
AggClauseCosts dummy_aggcosts;
/* Use all-zero per-aggregate costs if NULL is passed */
if (aggcosts == NULL)
{
Assert(aggstrategy == AGG_HASHED);
MemSet(&dummy_aggcosts, 0, sizeof(AggClauseCosts));
aggcosts = &dummy_aggcosts;
}
/*
* The transCost.per_tuple component of aggcosts should be charged once
* per input tuple, corresponding to the costs of evaluating the aggregate
* transfns and their input expressions. The finalCost.per_tuple component
* is charged once per output tuple, corresponding to the costs of
* evaluating the finalfns. Startup costs are of course charged but once.
*
* If we are grouping, we charge an additional cpu_operator_cost per
* grouping column per input tuple for grouping comparisons.
*
* We will produce a single output tuple if not grouping, and a tuple per
* group otherwise. We charge cpu_tuple_cost for each output tuple.
*
* Note: in this cost model, AGG_SORTED and AGG_HASHED have exactly the
* same total CPU cost, but AGG_SORTED has lower startup cost. If the
* input path is already sorted appropriately, AGG_SORTED should be
* preferred (since it has no risk of memory overflow). This will happen
* as long as the computed total costs are indeed exactly equal --- but if
* there's roundoff error we might do the wrong thing. So be sure that
* the computations below form the same intermediate values in the same
* order.
*/
if (aggstrategy == AGG_PLAIN)
{
startup_cost = input_total_cost;
startup_cost += aggcosts->transCost.startup;
startup_cost += aggcosts->transCost.per_tuple * input_tuples;
startup_cost += aggcosts->finalCost.startup;
startup_cost += aggcosts->finalCost.per_tuple;
/* we aren't grouping */
total_cost = startup_cost + cpu_tuple_cost;
output_tuples = 1;
}
else if (aggstrategy == AGG_SORTED || aggstrategy == AGG_MIXED)
{
/* Here we are able to deliver output on-the-fly */
startup_cost = input_startup_cost;
total_cost = input_total_cost;
if (aggstrategy == AGG_MIXED && !enable_hashagg)
{
startup_cost += disable_cost;
total_cost += disable_cost;
}
/* calcs phrased this way to match HASHED case, see note above */
total_cost += aggcosts->transCost.startup;
total_cost += aggcosts->transCost.per_tuple * input_tuples;
total_cost += (cpu_operator_cost * numGroupCols) * input_tuples;
total_cost += aggcosts->finalCost.startup;
total_cost += aggcosts->finalCost.per_tuple * numGroups;
total_cost += cpu_tuple_cost * numGroups;
output_tuples = numGroups;
}
else
{
/* must be AGG_HASHED */
startup_cost = input_total_cost;
if (!enable_hashagg)
startup_cost += disable_cost;
startup_cost += aggcosts->transCost.startup;
startup_cost += aggcosts->transCost.per_tuple * input_tuples;
/* cost of computing hash value */
startup_cost += (cpu_operator_cost * numGroupCols) * input_tuples;
startup_cost += aggcosts->finalCost.startup;
total_cost = startup_cost;
total_cost += aggcosts->finalCost.per_tuple * numGroups;
/* cost of retrieving from hash table */
total_cost += cpu_tuple_cost * numGroups;
output_tuples = numGroups;
}
/*
* Add the disk costs of hash aggregation that spills to disk.
*
* Groups that go into the hash table stay in memory until finalized, so
* spilling and reprocessing tuples doesn't incur additional invocations
* of transCost or finalCost. Furthermore, the computed hash value is
* stored with the spilled tuples, so we don't incur extra invocations of
* the hash function.
*
* Hash Agg begins returning tuples after the first batch is complete.
* Accrue writes (spilled tuples) to startup_cost and to total_cost;
* accrue reads only to total_cost.
*/
if (aggstrategy == AGG_HASHED || aggstrategy == AGG_MIXED)
{
double pages;
double pages_written = 0.0;
double pages_read = 0.0;
double hashentrysize;
double nbatches;
Size mem_limit;
uint64 ngroups_limit;
int num_partitions;
int depth;
/*
* Estimate number of batches based on the computed limits. If less
* than or equal to one, all groups are expected to fit in memory;
* otherwise we expect to spill.
*/
hashentrysize = hash_agg_entry_size(aggcosts->numAggs, input_width,
aggcosts->transitionSpace);
hash_agg_set_limits(hashentrysize, numGroups, 0, &mem_limit,
&ngroups_limit, &num_partitions);
nbatches = Max((numGroups * hashentrysize) / mem_limit,
numGroups / ngroups_limit);
nbatches = Max(ceil(nbatches), 1.0);
num_partitions = Max(num_partitions, 2);
/*
* The number of partitions can change at different levels of
* recursion; but for the purposes of this calculation assume it stays
* constant.
*/
depth = ceil(log(nbatches) / log(num_partitions));
/*
* Estimate number of pages read and written. For each level of
* recursion, a tuple must be written and then later read.
*/
pages = relation_byte_size(input_tuples, input_width) / BLCKSZ;
pages_written = pages_read = pages * depth;
startup_cost += pages_written * random_page_cost;
total_cost += pages_written * random_page_cost;
total_cost += pages_read * seq_page_cost;
}
/*
* If there are quals (HAVING quals), account for their cost and
* selectivity.
*/
if (quals)
{
QualCost qual_cost;
cost_qual_eval(&qual_cost, quals, root);
startup_cost += qual_cost.startup;
total_cost += qual_cost.startup + output_tuples * qual_cost.per_tuple;
output_tuples = clamp_row_est(output_tuples *
clauselist_selectivity(root,
quals,
0,
JOIN_INNER,
NULL));
}
path->rows = output_tuples;
path->startup_cost = startup_cost;
path->total_cost = total_cost;
}
/*
* cost_windowagg
* Determines and returns the cost of performing a WindowAgg plan node,
* including the cost of its input.
*
* Input is assumed already properly sorted.
*/
void
cost_windowagg(Path *path, PlannerInfo *root,
List *windowFuncs, int numPartCols, int numOrderCols,
Cost input_startup_cost, Cost input_total_cost,
double input_tuples)
{
Cost startup_cost;
Cost total_cost;
ListCell *lc;
startup_cost = input_startup_cost;
total_cost = input_total_cost;
/*
* Window functions are assumed to cost their stated execution cost, plus
* the cost of evaluating their input expressions, per tuple. Since they
* may in fact evaluate their inputs at multiple rows during each cycle,
* this could be a drastic underestimate; but without a way to know how
* many rows the window function will fetch, it's hard to do better. In
* any case, it's a good estimate for all the built-in window functions,
* so we'll just do this for now.
*/
foreach(lc, windowFuncs)
{
WindowFunc *wfunc = lfirst_node(WindowFunc, lc);
Cost wfunccost;
QualCost argcosts;
argcosts.startup = argcosts.per_tuple = 0;
add_function_cost(root, wfunc->winfnoid, (Node *) wfunc,
&argcosts);
startup_cost += argcosts.startup;
wfunccost = argcosts.per_tuple;
/* also add the input expressions' cost to per-input-row costs */
cost_qual_eval_node(&argcosts, (Node *) wfunc->args, root);
startup_cost += argcosts.startup;
wfunccost += argcosts.per_tuple;
/*
* Add the filter's cost to per-input-row costs. XXX We should reduce
* input expression costs according to filter selectivity.
*/
cost_qual_eval_node(&argcosts, (Node *) wfunc->aggfilter, root);
startup_cost += argcosts.startup;
wfunccost += argcosts.per_tuple;
total_cost += wfunccost * input_tuples;
}
/*
* We also charge cpu_operator_cost per grouping column per tuple for
* grouping comparisons, plus cpu_tuple_cost per tuple for general
* overhead.
*
* XXX this neglects costs of spooling the data to disk when it overflows
* work_mem. Sooner or later that should get accounted for.
*/
total_cost += cpu_operator_cost * (numPartCols + numOrderCols) * input_tuples;
total_cost += cpu_tuple_cost * input_tuples;
path->rows = input_tuples;
path->startup_cost = startup_cost;
path->total_cost = total_cost;
}
/*
* cost_group
* Determines and returns the cost of performing a Group plan node,
* including the cost of its input.
*
* Note: caller must ensure that input costs are for appropriately-sorted
* input.
*/
void
cost_group(Path *path, PlannerInfo *root,
int numGroupCols, double numGroups,
List *quals,
Cost input_startup_cost, Cost input_total_cost,
double input_tuples)
{
double output_tuples;
Cost startup_cost;
Cost total_cost;
output_tuples = numGroups;
startup_cost = input_startup_cost;
total_cost = input_total_cost;
/*
* Charge one cpu_operator_cost per comparison per input tuple. We assume
* all columns get compared at most of the tuples.
*/
total_cost += cpu_operator_cost * input_tuples * numGroupCols;
/*
* If there are quals (HAVING quals), account for their cost and
* selectivity.
*/
if (quals)
{
QualCost qual_cost;
cost_qual_eval(&qual_cost, quals, root);
startup_cost += qual_cost.startup;
total_cost += qual_cost.startup + output_tuples * qual_cost.per_tuple;
output_tuples = clamp_row_est(output_tuples *
clauselist_selectivity(root,
quals,
0,
JOIN_INNER,
NULL));
}
path->rows = output_tuples;
path->startup_cost = startup_cost;
path->total_cost = total_cost;
}
/*
* initial_cost_nestloop
* Preliminary estimate of the cost of a nestloop join path.
*
* This must quickly produce lower-bound estimates of the path's startup and
* total costs. If we are unable to eliminate the proposed path from
* consideration using the lower bounds, final_cost_nestloop will be called
* to obtain the final estimates.
*
* The exact division of labor between this function and final_cost_nestloop
* is private to them, and represents a tradeoff between speed of the initial
* estimate and getting a tight lower bound. We choose to not examine the
* join quals here, since that's by far the most expensive part of the
* calculations. The end result is that CPU-cost considerations must be
* left for the second phase; and for SEMI/ANTI joins, we must also postpone
* incorporation of the inner path's run cost.
*
* 'workspace' is to be filled with startup_cost, total_cost, and perhaps
* other data to be used by final_cost_nestloop
* 'jointype' is the type of join to be performed
* 'outer_path' is the outer input to the join
* 'inner_path' is the inner input to the join
* 'extra' contains miscellaneous information about the join
*/
void
initial_cost_nestloop(PlannerInfo *root, JoinCostWorkspace *workspace,
JoinType jointype,
Path *outer_path, Path *inner_path,
JoinPathExtraData *extra)
{
Cost startup_cost = 0;
Cost run_cost = 0;
double outer_path_rows = outer_path->rows;
Cost inner_rescan_start_cost;
Cost inner_rescan_total_cost;
Cost inner_run_cost;
Cost inner_rescan_run_cost;
/* estimate costs to rescan the inner relation */
cost_rescan(root, inner_path,
&inner_rescan_start_cost,
&inner_rescan_total_cost);
/* cost of source data */
/*
* NOTE: clearly, we must pay both outer and inner paths' startup_cost
* before we can start returning tuples, so the join's startup cost is
* their sum. We'll also pay the inner path's rescan startup cost
* multiple times.
*/
startup_cost += outer_path->startup_cost + inner_path->startup_cost;
run_cost += outer_path->total_cost - outer_path->startup_cost;
if (outer_path_rows > 1)
run_cost += (outer_path_rows - 1) * inner_rescan_start_cost;
inner_run_cost = inner_path->total_cost - inner_path->startup_cost;
inner_rescan_run_cost = inner_rescan_total_cost - inner_rescan_start_cost;
if (jointype == JOIN_SEMI || jointype == JOIN_ANTI ||
extra->inner_unique)
{
/*
* With a SEMI or ANTI join, or if the innerrel is known unique, the
* executor will stop after the first match.
*
* Getting decent estimates requires inspection of the join quals,
* which we choose to postpone to final_cost_nestloop.
*/
/* Save private data for final_cost_nestloop */
workspace->inner_run_cost = inner_run_cost;
workspace->inner_rescan_run_cost = inner_rescan_run_cost;
}
else
{
/* Normal case; we'll scan whole input rel for each outer row */
run_cost += inner_run_cost;
if (outer_path_rows > 1)
run_cost += (outer_path_rows - 1) * inner_rescan_run_cost;
}
/* CPU costs left for later */
/* Public result fields */
workspace->startup_cost = startup_cost;
workspace->total_cost = startup_cost + run_cost;
/* Save private data for final_cost_nestloop */
workspace->run_cost = run_cost;
}
/*
* final_cost_nestloop
* Final estimate of the cost and result size of a nestloop join path.
*
* 'path' is already filled in except for the rows and cost fields
* 'workspace' is the result from initial_cost_nestloop
* 'extra' contains miscellaneous information about the join
*/
void
final_cost_nestloop(PlannerInfo *root, NestPath *path,
JoinCostWorkspace *workspace,
JoinPathExtraData *extra)
{
Path *outer_path = path->outerjoinpath;
Path *inner_path = path->innerjoinpath;
double outer_path_rows = outer_path->rows;
double inner_path_rows = inner_path->rows;
Cost startup_cost = workspace->startup_cost;
Cost run_cost = workspace->run_cost;
Cost cpu_per_tuple;
QualCost restrict_qual_cost;
double ntuples;
/* Protect some assumptions below that rowcounts aren't zero or NaN */
if (outer_path_rows <= 0 || isnan(outer_path_rows))
outer_path_rows = 1;
if (inner_path_rows <= 0 || isnan(inner_path_rows))
inner_path_rows = 1;
/* Mark the path with the correct row estimate */
if (path->path.param_info)
path->path.rows = path->path.param_info->ppi_rows;
else
path->path.rows = path->path.parent->rows;
/* For partial paths, scale row estimate. */
if (path->path.parallel_workers > 0)
{
double parallel_divisor = get_parallel_divisor(&path->path);
path->path.rows =
clamp_row_est(path->path.rows / parallel_divisor);
}
/*
* We could include disable_cost in the preliminary estimate, but that
* would amount to optimizing for the case where the join method is
* disabled, which doesn't seem like the way to bet.
*/
if (!enable_nestloop)
startup_cost += disable_cost;
/* cost of inner-relation source data (we already dealt with outer rel) */
if (path->jointype == JOIN_SEMI || path->jointype == JOIN_ANTI ||
extra->inner_unique)
{
/*
* With a SEMI or ANTI join, or if the innerrel is known unique, the
* executor will stop after the first match.
*/
Cost inner_run_cost = workspace->inner_run_cost;
Cost inner_rescan_run_cost = workspace->inner_rescan_run_cost;
double outer_matched_rows;
double outer_unmatched_rows;
Selectivity inner_scan_frac;
/*
* For an outer-rel row that has at least one match, we can expect the
* inner scan to stop after a fraction 1/(match_count+1) of the inner
* rows, if the matches are evenly distributed. Since they probably
* aren't quite evenly distributed, we apply a fuzz factor of 2.0 to
* that fraction. (If we used a larger fuzz factor, we'd have to
* clamp inner_scan_frac to at most 1.0; but since match_count is at
* least 1, no such clamp is needed now.)
*/
outer_matched_rows = rint(outer_path_rows * extra->semifactors.outer_match_frac);
outer_unmatched_rows = outer_path_rows - outer_matched_rows;
inner_scan_frac = 2.0 / (extra->semifactors.match_count + 1.0);
/*
* Compute number of tuples processed (not number emitted!). First,
* account for successfully-matched outer rows.
*/
ntuples = outer_matched_rows * inner_path_rows * inner_scan_frac;
/*
* Now we need to estimate the actual costs of scanning the inner
* relation, which may be quite a bit less than N times inner_run_cost
* due to early scan stops. We consider two cases. If the inner path
* is an indexscan using all the joinquals as indexquals, then an
* unmatched outer row results in an indexscan returning no rows,
* which is probably quite cheap. Otherwise, the executor will have
* to scan the whole inner rel for an unmatched row; not so cheap.
*/
if (has_indexed_join_quals(path))
{
/*
* Successfully-matched outer rows will only require scanning
* inner_scan_frac of the inner relation. In this case, we don't
* need to charge the full inner_run_cost even when that's more
* than inner_rescan_run_cost, because we can assume that none of
* the inner scans ever scan the whole inner relation. So it's
* okay to assume that all the inner scan executions can be
* fractions of the full cost, even if materialization is reducing
* the rescan cost. At this writing, it's impossible to get here
* for a materialized inner scan, so inner_run_cost and
* inner_rescan_run_cost will be the same anyway; but just in
* case, use inner_run_cost for the first matched tuple and
* inner_rescan_run_cost for additional ones.
*/
run_cost += inner_run_cost * inner_scan_frac;
if (outer_matched_rows > 1)
run_cost += (outer_matched_rows - 1) * inner_rescan_run_cost * inner_scan_frac;
/*
* Add the cost of inner-scan executions for unmatched outer rows.
* We estimate this as the same cost as returning the first tuple
* of a nonempty scan. We consider that these are all rescans,
* since we used inner_run_cost once already.
*/
run_cost += outer_unmatched_rows *
inner_rescan_run_cost / inner_path_rows;
/*
* We won't be evaluating any quals at all for unmatched rows, so
* don't add them to ntuples.
*/
}
else
{
/*
* Here, a complicating factor is that rescans may be cheaper than
* first scans. If we never scan all the way to the end of the
* inner rel, it might be (depending on the plan type) that we'd
* never pay the whole inner first-scan run cost. However it is
* difficult to estimate whether that will happen (and it could
* not happen if there are any unmatched outer rows!), so be
* conservative and always charge the whole first-scan cost once.
* We consider this charge to correspond to the first unmatched
* outer row, unless there isn't one in our estimate, in which
* case blame it on the first matched row.
*/
/* First, count all unmatched join tuples as being processed */
ntuples += outer_unmatched_rows * inner_path_rows;
/* Now add the forced full scan, and decrement appropriate count */
run_cost += inner_run_cost;
if (outer_unmatched_rows >= 1)
outer_unmatched_rows -= 1;
else
outer_matched_rows -= 1;
/* Add inner run cost for additional outer tuples having matches */
if (outer_matched_rows > 0)
run_cost += outer_matched_rows * inner_rescan_run_cost * inner_scan_frac;
/* Add inner run cost for additional unmatched outer tuples */
if (outer_unmatched_rows > 0)
run_cost += outer_unmatched_rows * inner_rescan_run_cost;
}
}
else
{
/* Normal-case source costs were included in preliminary estimate */
/* Compute number of tuples processed (not number emitted!) */
ntuples = outer_path_rows * inner_path_rows;
}
/* CPU costs */
cost_qual_eval(&restrict_qual_cost, path->joinrestrictinfo, root);
startup_cost += restrict_qual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + restrict_qual_cost.per_tuple;
run_cost += cpu_per_tuple * ntuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->path.pathtarget->cost.startup;
run_cost += path->path.pathtarget->cost.per_tuple * path->path.rows;
path->path.startup_cost = startup_cost;
path->path.total_cost = startup_cost + run_cost;
}
/*
* initial_cost_mergejoin
* Preliminary estimate of the cost of a mergejoin path.
*
* This must quickly produce lower-bound estimates of the path's startup and
* total costs. If we are unable to eliminate the proposed path from
* consideration using the lower bounds, final_cost_mergejoin will be called
* to obtain the final estimates.
*
* The exact division of labor between this function and final_cost_mergejoin
* is private to them, and represents a tradeoff between speed of the initial
* estimate and getting a tight lower bound. We choose to not examine the
* join quals here, except for obtaining the scan selectivity estimate which
* is really essential (but fortunately, use of caching keeps the cost of
* getting that down to something reasonable).
* We also assume that cost_sort is cheap enough to use here.
*
* 'workspace' is to be filled with startup_cost, total_cost, and perhaps
* other data to be used by final_cost_mergejoin
* 'jointype' is the type of join to be performed
* 'mergeclauses' is the list of joinclauses to be used as merge clauses
* 'outer_path' is the outer input to the join
* 'inner_path' is the inner input to the join
* 'outersortkeys' is the list of sort keys for the outer path
* 'innersortkeys' is the list of sort keys for the inner path
* 'extra' contains miscellaneous information about the join
*
* Note: outersortkeys and innersortkeys should be NIL if no explicit
* sort is needed because the respective source path is already ordered.
*/
void
initial_cost_mergejoin(PlannerInfo *root, JoinCostWorkspace *workspace,
JoinType jointype,
List *mergeclauses,
Path *outer_path, Path *inner_path,
List *outersortkeys, List *innersortkeys,
JoinPathExtraData *extra)
{
Cost startup_cost = 0;
Cost run_cost = 0;
double outer_path_rows = outer_path->rows;
double inner_path_rows = inner_path->rows;
Cost inner_run_cost;
double outer_rows,
inner_rows,
outer_skip_rows,
inner_skip_rows;
Selectivity outerstartsel,
outerendsel,
innerstartsel,
innerendsel;
Path sort_path; /* dummy for result of cost_sort */
/* Protect some assumptions below that rowcounts aren't zero or NaN */
if (outer_path_rows <= 0 || isnan(outer_path_rows))
outer_path_rows = 1;
if (inner_path_rows <= 0 || isnan(inner_path_rows))
inner_path_rows = 1;
/*
* A merge join will stop as soon as it exhausts either input stream
* (unless it's an outer join, in which case the outer side has to be
* scanned all the way anyway). Estimate fraction of the left and right
* inputs that will actually need to be scanned. Likewise, we can
* estimate the number of rows that will be skipped before the first join
* pair is found, which should be factored into startup cost. We use only
* the first (most significant) merge clause for this purpose. Since
* mergejoinscansel() is a fairly expensive computation, we cache the
* results in the merge clause RestrictInfo.
*/
if (mergeclauses && jointype != JOIN_FULL)
{
RestrictInfo *firstclause = (RestrictInfo *) linitial(mergeclauses);
List *opathkeys;
List *ipathkeys;
PathKey *opathkey;
PathKey *ipathkey;
MergeScanSelCache *cache;
/* Get the input pathkeys to determine the sort-order details */
opathkeys = outersortkeys ? outersortkeys : outer_path->pathkeys;
ipathkeys = innersortkeys ? innersortkeys : inner_path->pathkeys;
Assert(opathkeys);
Assert(ipathkeys);
opathkey = (PathKey *) linitial(opathkeys);
ipathkey = (PathKey *) linitial(ipathkeys);
/* debugging check */
if (opathkey->pk_opfamily != ipathkey->pk_opfamily ||
opathkey->pk_eclass->ec_collation != ipathkey->pk_eclass->ec_collation ||
opathkey->pk_strategy != ipathkey->pk_strategy ||
opathkey->pk_nulls_first != ipathkey->pk_nulls_first)
elog(ERROR, "left and right pathkeys do not match in mergejoin");
/* Get the selectivity with caching */
cache = cached_scansel(root, firstclause, opathkey);
if (bms_is_subset(firstclause->left_relids,
outer_path->parent->relids))
{
/* left side of clause is outer */
outerstartsel = cache->leftstartsel;
outerendsel = cache->leftendsel;
innerstartsel = cache->rightstartsel;
innerendsel = cache->rightendsel;
}
else
{
/* left side of clause is inner */
outerstartsel = cache->rightstartsel;
outerendsel = cache->rightendsel;
innerstartsel = cache->leftstartsel;
innerendsel = cache->leftendsel;
}
if (jointype == JOIN_LEFT ||
jointype == JOIN_ANTI)
{
outerstartsel = 0.0;
outerendsel = 1.0;
}
else if (jointype == JOIN_RIGHT)
{
innerstartsel = 0.0;
innerendsel = 1.0;
}
}
else
{
/* cope with clauseless or full mergejoin */
outerstartsel = innerstartsel = 0.0;
outerendsel = innerendsel = 1.0;
}
/*
* Convert selectivities to row counts. We force outer_rows and
* inner_rows to be at least 1, but the skip_rows estimates can be zero.
*/
outer_skip_rows = rint(outer_path_rows * outerstartsel);
inner_skip_rows = rint(inner_path_rows * innerstartsel);
outer_rows = clamp_row_est(outer_path_rows * outerendsel);
inner_rows = clamp_row_est(inner_path_rows * innerendsel);
Assert(outer_skip_rows <= outer_rows);
Assert(inner_skip_rows <= inner_rows);
/*
* Readjust scan selectivities to account for above rounding. This is
* normally an insignificant effect, but when there are only a few rows in
* the inputs, failing to do this makes for a large percentage error.
*/
outerstartsel = outer_skip_rows / outer_path_rows;
innerstartsel = inner_skip_rows / inner_path_rows;
outerendsel = outer_rows / outer_path_rows;
innerendsel = inner_rows / inner_path_rows;
Assert(outerstartsel <= outerendsel);
Assert(innerstartsel <= innerendsel);
/* cost of source data */
if (outersortkeys) /* do we need to sort outer? */
{
cost_sort(&sort_path,
root,
outersortkeys,
outer_path->total_cost,
outer_path_rows,
outer_path->pathtarget->width,
0.0,
work_mem,
-1.0);
startup_cost += sort_path.startup_cost;
startup_cost += (sort_path.total_cost - sort_path.startup_cost)
* outerstartsel;
run_cost += (sort_path.total_cost - sort_path.startup_cost)
* (outerendsel - outerstartsel);
}
else
{
startup_cost += outer_path->startup_cost;
startup_cost += (outer_path->total_cost - outer_path->startup_cost)
* outerstartsel;
run_cost += (outer_path->total_cost - outer_path->startup_cost)
* (outerendsel - outerstartsel);
}
if (innersortkeys) /* do we need to sort inner? */
{
cost_sort(&sort_path,
root,
innersortkeys,
inner_path->total_cost,
inner_path_rows,
inner_path->pathtarget->width,
0.0,
work_mem,
-1.0);
startup_cost += sort_path.startup_cost;
startup_cost += (sort_path.total_cost - sort_path.startup_cost)
* innerstartsel;
inner_run_cost = (sort_path.total_cost - sort_path.startup_cost)
* (innerendsel - innerstartsel);
}
else
{
startup_cost += inner_path->startup_cost;
startup_cost += (inner_path->total_cost - inner_path->startup_cost)
* innerstartsel;
inner_run_cost = (inner_path->total_cost - inner_path->startup_cost)
* (innerendsel - innerstartsel);
}
/*
* We can't yet determine whether rescanning occurs, or whether
* materialization of the inner input should be done. The minimum
* possible inner input cost, regardless of rescan and materialization
* considerations, is inner_run_cost. We include that in
* workspace->total_cost, but not yet in run_cost.
*/
/* CPU costs left for later */
/* Public result fields */
workspace->startup_cost = startup_cost;
workspace->total_cost = startup_cost + run_cost + inner_run_cost;
/* Save private data for final_cost_mergejoin */
workspace->run_cost = run_cost;
workspace->inner_run_cost = inner_run_cost;
workspace->outer_rows = outer_rows;
workspace->inner_rows = inner_rows;
workspace->outer_skip_rows = outer_skip_rows;
workspace->inner_skip_rows = inner_skip_rows;
}
/*
* final_cost_mergejoin
* Final estimate of the cost and result size of a mergejoin path.
*
* Unlike other costsize functions, this routine makes two actual decisions:
* whether the executor will need to do mark/restore, and whether we should
* materialize the inner path. It would be logically cleaner to build
* separate paths testing these alternatives, but that would require repeating
* most of the cost calculations, which are not all that cheap. Since the
* choice will not affect output pathkeys or startup cost, only total cost,
* there is no possibility of wanting to keep more than one path. So it seems
* best to make the decisions here and record them in the path's
* skip_mark_restore and materialize_inner fields.
*
* Mark/restore overhead is usually required, but can be skipped if we know
* that the executor need find only one match per outer tuple, and that the
* mergeclauses are sufficient to identify a match.
*
* We materialize the inner path if we need mark/restore and either the inner
* path can't support mark/restore, or it's cheaper to use an interposed
* Material node to handle mark/restore.
*
* 'path' is already filled in except for the rows and cost fields and
* skip_mark_restore and materialize_inner
* 'workspace' is the result from initial_cost_mergejoin
* 'extra' contains miscellaneous information about the join
*/
void
final_cost_mergejoin(PlannerInfo *root, MergePath *path,
JoinCostWorkspace *workspace,
JoinPathExtraData *extra)
{
Path *outer_path = path->jpath.outerjoinpath;
Path *inner_path = path->jpath.innerjoinpath;
double inner_path_rows = inner_path->rows;
List *mergeclauses = path->path_mergeclauses;
List *innersortkeys = path->innersortkeys;
Cost startup_cost = workspace->startup_cost;
Cost run_cost = workspace->run_cost;
Cost inner_run_cost = workspace->inner_run_cost;
double outer_rows = workspace->outer_rows;
double inner_rows = workspace->inner_rows;
double outer_skip_rows = workspace->outer_skip_rows;
double inner_skip_rows = workspace->inner_skip_rows;
Cost cpu_per_tuple,
bare_inner_cost,
mat_inner_cost;
QualCost merge_qual_cost;
QualCost qp_qual_cost;
double mergejointuples,
rescannedtuples;
double rescanratio;
/* Protect some assumptions below that rowcounts aren't zero or NaN */
if (inner_path_rows <= 0 || isnan(inner_path_rows))
inner_path_rows = 1;
/* Mark the path with the correct row estimate */
if (path->jpath.path.param_info)
path->jpath.path.rows = path->jpath.path.param_info->ppi_rows;
else
path->jpath.path.rows = path->jpath.path.parent->rows;
/* For partial paths, scale row estimate. */
if (path->jpath.path.parallel_workers > 0)
{
double parallel_divisor = get_parallel_divisor(&path->jpath.path);
path->jpath.path.rows =
clamp_row_est(path->jpath.path.rows / parallel_divisor);
}
/*
* We could include disable_cost in the preliminary estimate, but that
* would amount to optimizing for the case where the join method is
* disabled, which doesn't seem like the way to bet.
*/
if (!enable_mergejoin)
startup_cost += disable_cost;
/*
* Compute cost of the mergequals and qpquals (other restriction clauses)
* separately.
*/
cost_qual_eval(&merge_qual_cost, mergeclauses, root);
cost_qual_eval(&qp_qual_cost, path->jpath.joinrestrictinfo, root);
qp_qual_cost.startup -= merge_qual_cost.startup;
qp_qual_cost.per_tuple -= merge_qual_cost.per_tuple;
/*
* With a SEMI or ANTI join, or if the innerrel is known unique, the
* executor will stop scanning for matches after the first match. When
* all the joinclauses are merge clauses, this means we don't ever need to
* back up the merge, and so we can skip mark/restore overhead.
*/
if ((path->jpath.jointype == JOIN_SEMI ||
path->jpath.jointype == JOIN_ANTI ||
extra->inner_unique) &&
(list_length(path->jpath.joinrestrictinfo) ==
list_length(path->path_mergeclauses)))
path->skip_mark_restore = true;
else
path->skip_mark_restore = false;
/*
* Get approx # tuples passing the mergequals. We use approx_tuple_count
* here because we need an estimate done with JOIN_INNER semantics.
*/
mergejointuples = approx_tuple_count(root, &path->jpath, mergeclauses);
/*
* When there are equal merge keys in the outer relation, the mergejoin
* must rescan any matching tuples in the inner relation. This means
* re-fetching inner tuples; we have to estimate how often that happens.
*
* For regular inner and outer joins, the number of re-fetches can be
* estimated approximately as size of merge join output minus size of
* inner relation. Assume that the distinct key values are 1, 2, ..., and
* denote the number of values of each key in the outer relation as m1,
* m2, ...; in the inner relation, n1, n2, ... Then we have
*
* size of join = m1 * n1 + m2 * n2 + ...
*
* number of rescanned tuples = (m1 - 1) * n1 + (m2 - 1) * n2 + ... = m1 *
* n1 + m2 * n2 + ... - (n1 + n2 + ...) = size of join - size of inner
* relation
*
* This equation works correctly for outer tuples having no inner match
* (nk = 0), but not for inner tuples having no outer match (mk = 0); we
* are effectively subtracting those from the number of rescanned tuples,
* when we should not. Can we do better without expensive selectivity
* computations?
*
* The whole issue is moot if we are working from a unique-ified outer
* input, or if we know we don't need to mark/restore at all.
*/
if (IsA(outer_path, UniquePath) || path->skip_mark_restore)
rescannedtuples = 0;
else
{
rescannedtuples = mergejointuples - inner_path_rows;
/* Must clamp because of possible underestimate */
if (rescannedtuples < 0)
rescannedtuples = 0;
}
/*
* We'll inflate various costs this much to account for rescanning. Note
* that this is to be multiplied by something involving inner_rows, or
* another number related to the portion of the inner rel we'll scan.
*/
rescanratio = 1.0 + (rescannedtuples / inner_rows);
/*
* Decide whether we want to materialize the inner input to shield it from
* mark/restore and performing re-fetches. Our cost model for regular
* re-fetches is that a re-fetch costs the same as an original fetch,
* which is probably an overestimate; but on the other hand we ignore the
* bookkeeping costs of mark/restore. Not clear if it's worth developing
* a more refined model. So we just need to inflate the inner run cost by
* rescanratio.
*/
bare_inner_cost = inner_run_cost * rescanratio;
/*
* When we interpose a Material node the re-fetch cost is assumed to be
* just cpu_operator_cost per tuple, independently of the underlying
* plan's cost; and we charge an extra cpu_operator_cost per original
* fetch as well. Note that we're assuming the materialize node will
* never spill to disk, since it only has to remember tuples back to the
* last mark. (If there are a huge number of duplicates, our other cost
* factors will make the path so expensive that it probably won't get
* chosen anyway.) So we don't use cost_rescan here.
*
* Note: keep this estimate in sync with create_mergejoin_plan's labeling
* of the generated Material node.
*/
mat_inner_cost = inner_run_cost +
cpu_operator_cost * inner_rows * rescanratio;
/*
* If we don't need mark/restore at all, we don't need materialization.
*/
if (path->skip_mark_restore)
path->materialize_inner = false;
/*
* Prefer materializing if it looks cheaper, unless the user has asked to
* suppress materialization.
*/
else if (enable_material && mat_inner_cost < bare_inner_cost)
path->materialize_inner = true;
/*
* Even if materializing doesn't look cheaper, we *must* do it if the
* inner path is to be used directly (without sorting) and it doesn't
* support mark/restore.
*
* Since the inner side must be ordered, and only Sorts and IndexScans can
* create order to begin with, and they both support mark/restore, you
* might think there's no problem --- but you'd be wrong. Nestloop and
* merge joins can *preserve* the order of their inputs, so they can be
* selected as the input of a mergejoin, and they don't support
* mark/restore at present.
*
* We don't test the value of enable_material here, because
* materialization is required for correctness in this case, and turning
* it off does not entitle us to deliver an invalid plan.
*/
else if (innersortkeys == NIL &&
!ExecSupportsMarkRestore(inner_path))
path->materialize_inner = true;
/*
* Also, force materializing if the inner path is to be sorted and the
* sort is expected to spill to disk. This is because the final merge
* pass can be done on-the-fly if it doesn't have to support mark/restore.
* We don't try to adjust the cost estimates for this consideration,
* though.
*
* Since materialization is a performance optimization in this case,
* rather than necessary for correctness, we skip it if enable_material is
* off.
*/
else if (enable_material && innersortkeys != NIL &&
relation_byte_size(inner_path_rows,
inner_path->pathtarget->width) >
(work_mem * 1024L))
path->materialize_inner = true;
else
path->materialize_inner = false;
/* Charge the right incremental cost for the chosen case */
if (path->materialize_inner)
run_cost += mat_inner_cost;
else
run_cost += bare_inner_cost;
/* CPU costs */
/*
* The number of tuple comparisons needed is approximately number of outer
* rows plus number of inner rows plus number of rescanned tuples (can we
* refine this?). At each one, we need to evaluate the mergejoin quals.
*/
startup_cost += merge_qual_cost.startup;
startup_cost += merge_qual_cost.per_tuple *
(outer_skip_rows + inner_skip_rows * rescanratio);
run_cost += merge_qual_cost.per_tuple *
((outer_rows - outer_skip_rows) +
(inner_rows - inner_skip_rows) * rescanratio);
/*
* For each tuple that gets through the mergejoin proper, we charge
* cpu_tuple_cost plus the cost of evaluating additional restriction
* clauses that are to be applied at the join. (This is pessimistic since
* not all of the quals may get evaluated at each tuple.)
*
* Note: we could adjust for SEMI/ANTI joins skipping some qual
* evaluations here, but it's probably not worth the trouble.
*/
startup_cost += qp_qual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qp_qual_cost.per_tuple;
run_cost += cpu_per_tuple * mergejointuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->jpath.path.pathtarget->cost.startup;
run_cost += path->jpath.path.pathtarget->cost.per_tuple * path->jpath.path.rows;
path->jpath.path.startup_cost = startup_cost;
path->jpath.path.total_cost = startup_cost + run_cost;
}
/*
* run mergejoinscansel() with caching
*/
static MergeScanSelCache *
cached_scansel(PlannerInfo *root, RestrictInfo *rinfo, PathKey *pathkey)
{
MergeScanSelCache *cache;
ListCell *lc;
Selectivity leftstartsel,
leftendsel,
rightstartsel,
rightendsel;
MemoryContext oldcontext;
/* Do we have this result already? */
foreach(lc, rinfo->scansel_cache)
{
cache = (MergeScanSelCache *) lfirst(lc);
if (cache->opfamily == pathkey->pk_opfamily &&
cache->collation == pathkey->pk_eclass->ec_collation &&
cache->strategy == pathkey->pk_strategy &&
cache->nulls_first == pathkey->pk_nulls_first)
return cache;
}
/* Nope, do the computation */
mergejoinscansel(root,
(Node *) rinfo->clause,
pathkey->pk_opfamily,
pathkey->pk_strategy,
pathkey->pk_nulls_first,
&leftstartsel,
&leftendsel,
&rightstartsel,
&rightendsel);
/* Cache the result in suitably long-lived workspace */
oldcontext = MemoryContextSwitchTo(root->planner_cxt);
cache = (MergeScanSelCache *) palloc(sizeof(MergeScanSelCache));
cache->opfamily = pathkey->pk_opfamily;
cache->collation = pathkey->pk_eclass->ec_collation;
cache->strategy = pathkey->pk_strategy;
cache->nulls_first = pathkey->pk_nulls_first;
cache->leftstartsel = leftstartsel;
cache->leftendsel = leftendsel;
cache->rightstartsel = rightstartsel;
cache->rightendsel = rightendsel;
rinfo->scansel_cache = lappend(rinfo->scansel_cache, cache);
MemoryContextSwitchTo(oldcontext);
return cache;
}
/*
* initial_cost_hashjoin
* Preliminary estimate of the cost of a hashjoin path.
*
* This must quickly produce lower-bound estimates of the path's startup and
* total costs. If we are unable to eliminate the proposed path from
* consideration using the lower bounds, final_cost_hashjoin will be called
* to obtain the final estimates.
*
* The exact division of labor between this function and final_cost_hashjoin
* is private to them, and represents a tradeoff between speed of the initial
* estimate and getting a tight lower bound. We choose to not examine the
* join quals here (other than by counting the number of hash clauses),
* so we can't do much with CPU costs. We do assume that
* ExecChooseHashTableSize is cheap enough to use here.
*
* 'workspace' is to be filled with startup_cost, total_cost, and perhaps
* other data to be used by final_cost_hashjoin
* 'jointype' is the type of join to be performed
* 'hashclauses' is the list of joinclauses to be used as hash clauses
* 'outer_path' is the outer input to the join
* 'inner_path' is the inner input to the join
* 'extra' contains miscellaneous information about the join
* 'parallel_hash' indicates that inner_path is partial and that a shared
* hash table will be built in parallel
*/
void
initial_cost_hashjoin(PlannerInfo *root, JoinCostWorkspace *workspace,
JoinType jointype,
List *hashclauses,
Path *outer_path, Path *inner_path,
JoinPathExtraData *extra,
bool parallel_hash)
{
Cost startup_cost = 0;
Cost run_cost = 0;
double outer_path_rows = outer_path->rows;
double inner_path_rows = inner_path->rows;
double inner_path_rows_total = inner_path_rows;
int num_hashclauses = list_length(hashclauses);
int numbuckets;
int numbatches;
int num_skew_mcvs;
size_t space_allowed; /* unused */
/* cost of source data */
startup_cost += outer_path->startup_cost;
run_cost += outer_path->total_cost - outer_path->startup_cost;
startup_cost += inner_path->total_cost;
/*
* Cost of computing hash function: must do it once per input tuple. We
* charge one cpu_operator_cost for each column's hash function. Also,
* tack on one cpu_tuple_cost per inner row, to model the costs of
* inserting the row into the hashtable.
*
* XXX when a hashclause is more complex than a single operator, we really
* should charge the extra eval costs of the left or right side, as
* appropriate, here. This seems more work than it's worth at the moment.
*/
startup_cost += (cpu_operator_cost * num_hashclauses + cpu_tuple_cost)
* inner_path_rows;
run_cost += cpu_operator_cost * num_hashclauses * outer_path_rows;
/*
* If this is a parallel hash build, then the value we have for
* inner_rows_total currently refers only to the rows returned by each
* participant. For shared hash table size estimation, we need the total
* number, so we need to undo the division.
*/
if (parallel_hash)
inner_path_rows_total *= get_parallel_divisor(inner_path);
/*
* Get hash table size that executor would use for inner relation.
*
* XXX for the moment, always assume that skew optimization will be
* performed. As long as SKEW_HASH_MEM_PERCENT is small, it's not worth
* trying to determine that for sure.
*
* XXX at some point it might be interesting to try to account for skew
* optimization in the cost estimate, but for now, we don't.
*/
ExecChooseHashTableSize(inner_path_rows_total,
inner_path->pathtarget->width,
true, /* useskew */
parallel_hash, /* try_combined_hash_mem */
outer_path->parallel_workers,
&space_allowed,
&numbuckets,
&numbatches,
&num_skew_mcvs);
/*
* If inner relation is too big then we will need to "batch" the join,
* which implies writing and reading most of the tuples to disk an extra
* time. Charge seq_page_cost per page, since the I/O should be nice and
* sequential. Writing the inner rel counts as startup cost, all the rest
* as run cost.
*/
if (numbatches > 1)
{
double outerpages = page_size(outer_path_rows,
outer_path->pathtarget->width);
double innerpages = page_size(inner_path_rows,
inner_path->pathtarget->width);
startup_cost += seq_page_cost * innerpages;
run_cost += seq_page_cost * (innerpages + 2 * outerpages);
}
/* CPU costs left for later */
/* Public result fields */
workspace->startup_cost = startup_cost;
workspace->total_cost = startup_cost + run_cost;
/* Save private data for final_cost_hashjoin */
workspace->run_cost = run_cost;
workspace->numbuckets = numbuckets;
workspace->numbatches = numbatches;
workspace->inner_rows_total = inner_path_rows_total;
}
/*
* final_cost_hashjoin
* Final estimate of the cost and result size of a hashjoin path.
*
* Note: the numbatches estimate is also saved into 'path' for use later
*
* 'path' is already filled in except for the rows and cost fields and
* num_batches
* 'workspace' is the result from initial_cost_hashjoin
* 'extra' contains miscellaneous information about the join
*/
void
final_cost_hashjoin(PlannerInfo *root, HashPath *path,
JoinCostWorkspace *workspace,
JoinPathExtraData *extra)
{
Path *outer_path = path->jpath.outerjoinpath;
Path *inner_path = path->jpath.innerjoinpath;
double outer_path_rows = outer_path->rows;
double inner_path_rows = inner_path->rows;
double inner_path_rows_total = workspace->inner_rows_total;
List *hashclauses = path->path_hashclauses;
Cost startup_cost = workspace->startup_cost;
Cost run_cost = workspace->run_cost;
int numbuckets = workspace->numbuckets;
int numbatches = workspace->numbatches;
int hash_mem;
Cost cpu_per_tuple;
QualCost hash_qual_cost;
QualCost qp_qual_cost;
double hashjointuples;
double virtualbuckets;
Selectivity innerbucketsize;
Selectivity innermcvfreq;
ListCell *hcl;
/* Mark the path with the correct row estimate */
if (path->jpath.path.param_info)
path->jpath.path.rows = path->jpath.path.param_info->ppi_rows;
else
path->jpath.path.rows = path->jpath.path.parent->rows;
/* For partial paths, scale row estimate. */
if (path->jpath.path.parallel_workers > 0)
{
double parallel_divisor = get_parallel_divisor(&path->jpath.path);
path->jpath.path.rows =
clamp_row_est(path->jpath.path.rows / parallel_divisor);
}
/*
* We could include disable_cost in the preliminary estimate, but that
* would amount to optimizing for the case where the join method is
* disabled, which doesn't seem like the way to bet.
*/
if (!enable_hashjoin)
startup_cost += disable_cost;
/* mark the path with estimated # of batches */
path->num_batches = numbatches;
/* store the total number of tuples (sum of partial row estimates) */
path->inner_rows_total = inner_path_rows_total;
/* and compute the number of "virtual" buckets in the whole join */
virtualbuckets = (double) numbuckets * (double) numbatches;
/*
* Determine bucketsize fraction and MCV frequency for the inner relation.
* We use the smallest bucketsize or MCV frequency estimated for any
* individual hashclause; this is undoubtedly conservative.
*
* BUT: if inner relation has been unique-ified, we can assume it's good
* for hashing. This is important both because it's the right answer, and
* because we avoid contaminating the cache with a value that's wrong for
* non-unique-ified paths.
*/
if (IsA(inner_path, UniquePath))
{
innerbucketsize = 1.0 / virtualbuckets;
innermcvfreq = 0.0;
}
else
{
innerbucketsize = 1.0;
innermcvfreq = 1.0;
foreach(hcl, hashclauses)
{
RestrictInfo *restrictinfo = lfirst_node(RestrictInfo, hcl);
Selectivity thisbucketsize;
Selectivity thismcvfreq;
/*
* First we have to figure out which side of the hashjoin clause
* is the inner side.
*
* Since we tend to visit the same clauses over and over when
* planning a large query, we cache the bucket stats estimates in
* the RestrictInfo node to avoid repeated lookups of statistics.
*/
if (bms_is_subset(restrictinfo->right_relids,
inner_path->parent->relids))
{
/* righthand side is inner */
thisbucketsize = restrictinfo->right_bucketsize;
if (thisbucketsize < 0)
{
/* not cached yet */
estimate_hash_bucket_stats(root,
get_rightop(restrictinfo->clause),
virtualbuckets,
&restrictinfo->right_mcvfreq,
&restrictinfo->right_bucketsize);
thisbucketsize = restrictinfo->right_bucketsize;
}
thismcvfreq = restrictinfo->right_mcvfreq;
}
else
{
Assert(bms_is_subset(restrictinfo->left_relids,
inner_path->parent->relids));
/* lefthand side is inner */
thisbucketsize = restrictinfo->left_bucketsize;
if (thisbucketsize < 0)
{
/* not cached yet */
estimate_hash_bucket_stats(root,
get_leftop(restrictinfo->clause),
virtualbuckets,
&restrictinfo->left_mcvfreq,
&restrictinfo->left_bucketsize);
thisbucketsize = restrictinfo->left_bucketsize;
}
thismcvfreq = restrictinfo->left_mcvfreq;
}
if (innerbucketsize > thisbucketsize)
innerbucketsize = thisbucketsize;
if (innermcvfreq > thismcvfreq)
innermcvfreq = thismcvfreq;
}
}
/*
* If the bucket holding the inner MCV would exceed hash_mem, we don't
* want to hash unless there is really no other alternative, so apply
* disable_cost. (The executor normally copes with excessive memory usage
* by splitting batches, but obviously it cannot separate equal values
* that way, so it will be unable to drive the batch size below hash_mem
* when this is true.)
*/
hash_mem = get_hash_mem();
if (relation_byte_size(clamp_row_est(inner_path_rows * innermcvfreq),
inner_path->pathtarget->width) >
(hash_mem * 1024L))
startup_cost += disable_cost;
/*
* Compute cost of the hashquals and qpquals (other restriction clauses)
* separately.
*/
cost_qual_eval(&hash_qual_cost, hashclauses, root);
cost_qual_eval(&qp_qual_cost, path->jpath.joinrestrictinfo, root);
qp_qual_cost.startup -= hash_qual_cost.startup;
qp_qual_cost.per_tuple -= hash_qual_cost.per_tuple;
/* CPU costs */
if (path->jpath.jointype == JOIN_SEMI ||
path->jpath.jointype == JOIN_ANTI ||
extra->inner_unique)
{
double outer_matched_rows;
Selectivity inner_scan_frac;
/*
* With a SEMI or ANTI join, or if the innerrel is known unique, the
* executor will stop after the first match.
*
* For an outer-rel row that has at least one match, we can expect the
* bucket scan to stop after a fraction 1/(match_count+1) of the
* bucket's rows, if the matches are evenly distributed. Since they
* probably aren't quite evenly distributed, we apply a fuzz factor of
* 2.0 to that fraction. (If we used a larger fuzz factor, we'd have
* to clamp inner_scan_frac to at most 1.0; but since match_count is
* at least 1, no such clamp is needed now.)
*/
outer_matched_rows = rint(outer_path_rows * extra->semifactors.outer_match_frac);
inner_scan_frac = 2.0 / (extra->semifactors.match_count + 1.0);
startup_cost += hash_qual_cost.startup;
run_cost += hash_qual_cost.per_tuple * outer_matched_rows *
clamp_row_est(inner_path_rows * innerbucketsize * inner_scan_frac) * 0.5;
/*
* For unmatched outer-rel rows, the picture is quite a lot different.
* In the first place, there is no reason to assume that these rows
* preferentially hit heavily-populated buckets; instead assume they
* are uncorrelated with the inner distribution and so they see an
* average bucket size of inner_path_rows / virtualbuckets. In the
* second place, it seems likely that they will have few if any exact
* hash-code matches and so very few of the tuples in the bucket will
* actually require eval of the hash quals. We don't have any good
* way to estimate how many will, but for the moment assume that the
* effective cost per bucket entry is one-tenth what it is for
* matchable tuples.
*/
run_cost += hash_qual_cost.per_tuple *
(outer_path_rows - outer_matched_rows) *
clamp_row_est(inner_path_rows / virtualbuckets) * 0.05;
/* Get # of tuples that will pass the basic join */
if (path->jpath.jointype == JOIN_ANTI)
hashjointuples = outer_path_rows - outer_matched_rows;
else
hashjointuples = outer_matched_rows;
}
else
{
/*
* The number of tuple comparisons needed is the number of outer
* tuples times the typical number of tuples in a hash bucket, which
* is the inner relation size times its bucketsize fraction. At each
* one, we need to evaluate the hashjoin quals. But actually,
* charging the full qual eval cost at each tuple is pessimistic,
* since we don't evaluate the quals unless the hash values match
* exactly. For lack of a better idea, halve the cost estimate to
* allow for that.
*/
startup_cost += hash_qual_cost.startup;
run_cost += hash_qual_cost.per_tuple * outer_path_rows *
clamp_row_est(inner_path_rows * innerbucketsize) * 0.5;
/*
* Get approx # tuples passing the hashquals. We use
* approx_tuple_count here because we need an estimate done with
* JOIN_INNER semantics.
*/
hashjointuples = approx_tuple_count(root, &path->jpath, hashclauses);
}
/*
* For each tuple that gets through the hashjoin proper, we charge
* cpu_tuple_cost plus the cost of evaluating additional restriction
* clauses that are to be applied at the join. (This is pessimistic since
* not all of the quals may get evaluated at each tuple.)
*/
startup_cost += qp_qual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qp_qual_cost.per_tuple;
run_cost += cpu_per_tuple * hashjointuples;
/* tlist eval costs are paid per output row, not per tuple scanned */
startup_cost += path->jpath.path.pathtarget->cost.startup;
run_cost += path->jpath.path.pathtarget->cost.per_tuple * path->jpath.path.rows;
path->jpath.path.startup_cost = startup_cost;
path->jpath.path.total_cost = startup_cost + run_cost;
}
/*
* cost_subplan
* Figure the costs for a SubPlan (or initplan).
*
* Note: we could dig the subplan's Plan out of the root list, but in practice
* all callers have it handy already, so we make them pass it.
*/
void
cost_subplan(PlannerInfo *root, SubPlan *subplan, Plan *plan)
{
QualCost sp_cost;
/* Figure any cost for evaluating the testexpr */
cost_qual_eval(&sp_cost,
make_ands_implicit((Expr *) subplan->testexpr),
root);
if (subplan->useHashTable)
{
/*
* If we are using a hash table for the subquery outputs, then the
* cost of evaluating the query is a one-time cost. We charge one
* cpu_operator_cost per tuple for the work of loading the hashtable,
* too.
*/
sp_cost.startup += plan->total_cost +
cpu_operator_cost * plan->plan_rows;
/*
* The per-tuple costs include the cost of evaluating the lefthand
* expressions, plus the cost of probing the hashtable. We already
* accounted for the lefthand expressions as part of the testexpr, and
* will also have counted one cpu_operator_cost for each comparison
* operator. That is probably too low for the probing cost, but it's
* hard to make a better estimate, so live with it for now.
*/
}
else
{
/*
* Otherwise we will be rescanning the subplan output on each
* evaluation. We need to estimate how much of the output we will
* actually need to scan. NOTE: this logic should agree with the
* tuple_fraction estimates used by make_subplan() in
* plan/subselect.c.
*/
Cost plan_run_cost = plan->total_cost - plan->startup_cost;
if (subplan->subLinkType == EXISTS_SUBLINK)
{
/* we only need to fetch 1 tuple; clamp to avoid zero divide */
sp_cost.per_tuple += plan_run_cost / clamp_row_est(plan->plan_rows);
}
else if (subplan->subLinkType == ALL_SUBLINK ||
subplan->subLinkType == ANY_SUBLINK)
{
/* assume we need 50% of the tuples */
sp_cost.per_tuple += 0.50 * plan_run_cost;
/* also charge a cpu_operator_cost per row examined */
sp_cost.per_tuple += 0.50 * plan->plan_rows * cpu_operator_cost;
}
else
{
/* assume we need all tuples */
sp_cost.per_tuple += plan_run_cost;
}
/*
* Also account for subplan's startup cost. If the subplan is
* uncorrelated or undirect correlated, AND its topmost node is one
* that materializes its output, assume that we'll only need to pay
* its startup cost once; otherwise assume we pay the startup cost
* every time.
*/
if (subplan->parParam == NIL &&
ExecMaterializesOutput(nodeTag(plan)))
sp_cost.startup += plan->startup_cost;
else
sp_cost.per_tuple += plan->startup_cost;
}
subplan->startup_cost = sp_cost.startup;
subplan->per_call_cost = sp_cost.per_tuple;
}
/*
* cost_rescan
* Given a finished Path, estimate the costs of rescanning it after
* having done so the first time. For some Path types a rescan is
* cheaper than an original scan (if no parameters change), and this
* function embodies knowledge about that. The default is to return
* the same costs stored in the Path. (Note that the cost estimates
* actually stored in Paths are always for first scans.)
*
* This function is not currently intended to model effects such as rescans
* being cheaper due to disk block caching; what we are concerned with is
* plan types wherein the executor caches results explicitly, or doesn't
* redo startup calculations, etc.
*/
static void
cost_rescan(PlannerInfo *root, Path *path,
Cost *rescan_startup_cost, /* output parameters */
Cost *rescan_total_cost)
{
switch (path->pathtype)
{
case T_FunctionScan:
/*
* Currently, nodeFunctionscan.c always executes the function to
* completion before returning any rows, and caches the results in
* a tuplestore. So the function eval cost is all startup cost
* and isn't paid over again on rescans. However, all run costs
* will be paid over again.
*/
*rescan_startup_cost = 0;
*rescan_total_cost = path->total_cost - path->startup_cost;
break;
case T_HashJoin:
/*
* If it's a single-batch join, we don't need to rebuild the hash
* table during a rescan.
*/
if (((HashPath *) path)->num_batches == 1)
{
/* Startup cost is exactly the cost of hash table building */
*rescan_startup_cost = 0;
*rescan_total_cost = path->total_cost - path->startup_cost;
}
else
{
/* Otherwise, no special treatment */
*rescan_startup_cost = path->startup_cost;
*rescan_total_cost = path->total_cost;
}
break;
case T_CteScan:
case T_WorkTableScan:
{
/*
* These plan types materialize their final result in a
* tuplestore or tuplesort object. So the rescan cost is only
* cpu_tuple_cost per tuple, unless the result is large enough
* to spill to disk.
*/
Cost run_cost = cpu_tuple_cost * path->rows;
double nbytes = relation_byte_size(path->rows,
path->pathtarget->width);
long work_mem_bytes = work_mem * 1024L;
if (nbytes > work_mem_bytes)
{
/* It will spill, so account for re-read cost */
double npages = ceil(nbytes / BLCKSZ);
run_cost += seq_page_cost * npages;
}
*rescan_startup_cost = 0;
*rescan_total_cost = run_cost;
}
break;
case T_Material:
case T_Sort:
{
/*
* These plan types not only materialize their results, but do
* not implement qual filtering or projection. So they are
* even cheaper to rescan than the ones above. We charge only
* cpu_operator_cost per tuple. (Note: keep that in sync with
* the run_cost charge in cost_sort, and also see comments in
* cost_material before you change it.)
*/
Cost run_cost = cpu_operator_cost * path->rows;
double nbytes = relation_byte_size(path->rows,
path->pathtarget->width);
long work_mem_bytes = work_mem * 1024L;
if (nbytes > work_mem_bytes)
{
/* It will spill, so account for re-read cost */
double npages = ceil(nbytes / BLCKSZ);
run_cost += seq_page_cost * npages;
}
*rescan_startup_cost = 0;
*rescan_total_cost = run_cost;
}
break;
default:
*rescan_startup_cost = path->startup_cost;
*rescan_total_cost = path->total_cost;
break;
}
}
/*
* cost_qual_eval
* Estimate the CPU costs of evaluating a WHERE clause.
* The input can be either an implicitly-ANDed list of boolean
* expressions, or a list of RestrictInfo nodes. (The latter is
* preferred since it allows caching of the results.)
* The result includes both a one-time (startup) component,
* and a per-evaluation component.
*/
void
cost_qual_eval(QualCost *cost, List *quals, PlannerInfo *root)
{
cost_qual_eval_context context;
ListCell *l;
context.root = root;
context.total.startup = 0;
context.total.per_tuple = 0;
/* We don't charge any cost for the implicit ANDing at top level ... */
foreach(l, quals)
{
Node *qual = (Node *) lfirst(l);
cost_qual_eval_walker(qual, &context);
}
*cost = context.total;
}
/*
* cost_qual_eval_node
* As above, for a single RestrictInfo or expression.
*/
void
cost_qual_eval_node(QualCost *cost, Node *qual, PlannerInfo *root)
{
cost_qual_eval_context context;
context.root = root;
context.total.startup = 0;
context.total.per_tuple = 0;
cost_qual_eval_walker(qual, &context);
*cost = context.total;
}
static bool
cost_qual_eval_walker(Node *node, cost_qual_eval_context *context)
{
if (node == NULL)
return false;
/*
* RestrictInfo nodes contain an eval_cost field reserved for this
* routine's use, so that it's not necessary to evaluate the qual clause's
* cost more than once. If the clause's cost hasn't been computed yet,
* the field's startup value will contain -1.
*/
if (IsA(node, RestrictInfo))
{
RestrictInfo *rinfo = (RestrictInfo *) node;
if (rinfo->eval_cost.startup < 0)
{
cost_qual_eval_context locContext;
locContext.root = context->root;
locContext.total.startup = 0;
locContext.total.per_tuple = 0;
/*
* For an OR clause, recurse into the marked-up tree so that we
* set the eval_cost for contained RestrictInfos too.
*/
if (rinfo->orclause)
cost_qual_eval_walker((Node *) rinfo->orclause, &locContext);
else
cost_qual_eval_walker((Node *) rinfo->clause, &locContext);
/*
* If the RestrictInfo is marked pseudoconstant, it will be tested
* only once, so treat its cost as all startup cost.
*/
if (rinfo->pseudoconstant)
{
/* count one execution during startup */
locContext.total.startup += locContext.total.per_tuple;
locContext.total.per_tuple = 0;
}
rinfo->eval_cost = locContext.total;
}
context->total.startup += rinfo->eval_cost.startup;
context->total.per_tuple += rinfo->eval_cost.per_tuple;
/* do NOT recurse into children */
return false;
}
/*
* For each operator or function node in the given tree, we charge the
* estimated execution cost given by pg_proc.procost (remember to multiply
* this by cpu_operator_cost).
*
* Vars and Consts are charged zero, and so are boolean operators (AND,
* OR, NOT). Simplistic, but a lot better than no model at all.
*
* Should we try to account for the possibility of short-circuit
* evaluation of AND/OR? Probably *not*, because that would make the
* results depend on the clause ordering, and we are not in any position
* to expect that the current ordering of the clauses is the one that's
* going to end up being used. The above per-RestrictInfo caching would
* not mix well with trying to re-order clauses anyway.
*
* Another issue that is entirely ignored here is that if a set-returning
* function is below top level in the tree, the functions/operators above
* it will need to be evaluated multiple times. In practical use, such
* cases arise so seldom as to not be worth the added complexity needed;
* moreover, since our rowcount estimates for functions tend to be pretty
* phony, the results would also be pretty phony.
*/
if (IsA(node, FuncExpr))
{
add_function_cost(context->root, ((FuncExpr *) node)->funcid, node,
&context->total);
}
else if (IsA(node, OpExpr) ||
IsA(node, DistinctExpr) ||
IsA(node, NullIfExpr))
{
/* rely on struct equivalence to treat these all alike */
set_opfuncid((OpExpr *) node);
add_function_cost(context->root, ((OpExpr *) node)->opfuncid, node,
&context->total);
}
else if (IsA(node, ScalarArrayOpExpr))
{
/*
* Estimate that the operator will be applied to about half of the
* array elements before the answer is determined.
*/
ScalarArrayOpExpr *saop = (ScalarArrayOpExpr *) node;
Node *arraynode = (Node *) lsecond(saop->args);
QualCost sacosts;
set_sa_opfuncid(saop);
sacosts.startup = sacosts.per_tuple = 0;
add_function_cost(context->root, saop->opfuncid, NULL,
&sacosts);
context->total.startup += sacosts.startup;
context->total.per_tuple += sacosts.per_tuple *
estimate_array_length(arraynode) * 0.5;
}
else if (IsA(node, Aggref) ||
IsA(node, WindowFunc))
{
/*
* Aggref and WindowFunc nodes are (and should be) treated like Vars,
* ie, zero execution cost in the current model, because they behave
* essentially like Vars at execution. We disregard the costs of
* their input expressions for the same reason. The actual execution
* costs of the aggregate/window functions and their arguments have to
* be factored into plan-node-specific costing of the Agg or WindowAgg
* plan node.
*/
return false; /* don't recurse into children */
}
else if (IsA(node, CoerceViaIO))
{
CoerceViaIO *iocoerce = (CoerceViaIO *) node;
Oid iofunc;
Oid typioparam;
bool typisvarlena;
/* check the result type's input function */
getTypeInputInfo(iocoerce->resulttype,
&iofunc, &typioparam);
add_function_cost(context->root, iofunc, NULL,
&context->total);
/* check the input type's output function */
getTypeOutputInfo(exprType((Node *) iocoerce->arg),
&iofunc, &typisvarlena);
add_function_cost(context->root, iofunc, NULL,
&context->total);
}
else if (IsA(node, ArrayCoerceExpr))
{
ArrayCoerceExpr *acoerce = (ArrayCoerceExpr *) node;
QualCost perelemcost;
cost_qual_eval_node(&perelemcost, (Node *) acoerce->elemexpr,
context->root);
context->total.startup += perelemcost.startup;
if (perelemcost.per_tuple > 0)
context->total.per_tuple += perelemcost.per_tuple *
estimate_array_length((Node *) acoerce->arg);
}
else if (IsA(node, RowCompareExpr))
{
/* Conservatively assume we will check all the columns */
RowCompareExpr *rcexpr = (RowCompareExpr *) node;
ListCell *lc;
foreach(lc, rcexpr->opnos)
{
Oid opid = lfirst_oid(lc);
add_function_cost(context->root, get_opcode(opid), NULL,
&context->total);
}
}
else if (IsA(node, MinMaxExpr) ||
IsA(node, SQLValueFunction) ||
IsA(node, XmlExpr) ||
IsA(node, CoerceToDomain) ||
IsA(node, NextValueExpr))
{
/* Treat all these as having cost 1 */
context->total.per_tuple += cpu_operator_cost;
}
else if (IsA(node, CurrentOfExpr))
{
/* Report high cost to prevent selection of anything but TID scan */
context->total.startup += disable_cost;
}
else if (IsA(node, SubLink))
{
/* This routine should not be applied to un-planned expressions */
elog(ERROR, "cannot handle unplanned sub-select");
}
else if (IsA(node, SubPlan))
{
/*
* A subplan node in an expression typically indicates that the
* subplan will be executed on each evaluation, so charge accordingly.
* (Sub-selects that can be executed as InitPlans have already been
* removed from the expression.)
*/
SubPlan *subplan = (SubPlan *) node;
context->total.startup += subplan->startup_cost;
context->total.per_tuple += subplan->per_call_cost;
/*
* We don't want to recurse into the testexpr, because it was already
* counted in the SubPlan node's costs. So we're done.
*/
return false;
}
else if (IsA(node, AlternativeSubPlan))
{
/*
* Arbitrarily use the first alternative plan for costing. (We should
* certainly only include one alternative, and we don't yet have
* enough information to know which one the executor is most likely to
* use.)
*/
AlternativeSubPlan *asplan = (AlternativeSubPlan *) node;
return cost_qual_eval_walker((Node *) linitial(asplan->subplans),
context);
}
else if (IsA(node, PlaceHolderVar))
{
/*
* A PlaceHolderVar should be given cost zero when considering general
* expression evaluation costs. The expense of doing the contained
* expression is charged as part of the tlist eval costs of the scan
* or join where the PHV is first computed (see set_rel_width and
* add_placeholders_to_joinrel). If we charged it again here, we'd be
* double-counting the cost for each level of plan that the PHV
* bubbles up through. Hence, return without recursing into the
* phexpr.
*/
return false;
}
/* recurse into children */
return expression_tree_walker(node, cost_qual_eval_walker,
(void *) context);
}
/*
* get_restriction_qual_cost
* Compute evaluation costs of a baserel's restriction quals, plus any
* movable join quals that have been pushed down to the scan.
* Results are returned into *qpqual_cost.
*
* This is a convenience subroutine that works for seqscans and other cases
* where all the given quals will be evaluated the hard way. It's not useful
* for cost_index(), for example, where the index machinery takes care of
* some of the quals. We assume baserestrictcost was previously set by
* set_baserel_size_estimates().
*/
static void
get_restriction_qual_cost(PlannerInfo *root, RelOptInfo *baserel,
ParamPathInfo *param_info,
QualCost *qpqual_cost)
{
if (param_info)
{
/* Include costs of pushed-down clauses */
cost_qual_eval(qpqual_cost, param_info->ppi_clauses, root);
qpqual_cost->startup += baserel->baserestrictcost.startup;
qpqual_cost->per_tuple += baserel->baserestrictcost.per_tuple;
}
else
*qpqual_cost = baserel->baserestrictcost;
}
/*
* compute_semi_anti_join_factors
* Estimate how much of the inner input a SEMI, ANTI, or inner_unique join
* can be expected to scan.
*
* In a hash or nestloop SEMI/ANTI join, the executor will stop scanning
* inner rows as soon as it finds a match to the current outer row.
* The same happens if we have detected the inner rel is unique.
* We should therefore adjust some of the cost components for this effect.
* This function computes some estimates needed for these adjustments.
* These estimates will be the same regardless of the particular paths used
* for the outer and inner relation, so we compute these once and then pass
* them to all the join cost estimation functions.
*
* Input parameters:
* joinrel: join relation under consideration
* outerrel: outer relation under consideration
* innerrel: inner relation under consideration
* jointype: if not JOIN_SEMI or JOIN_ANTI, we assume it's inner_unique
* sjinfo: SpecialJoinInfo relevant to this join
* restrictlist: join quals
* Output parameters:
* *semifactors is filled in (see pathnodes.h for field definitions)
*/
void
compute_semi_anti_join_factors(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
JoinType jointype,
SpecialJoinInfo *sjinfo,
List *restrictlist,
SemiAntiJoinFactors *semifactors)
{
Selectivity jselec;
Selectivity nselec;
Selectivity avgmatch;
SpecialJoinInfo norm_sjinfo;
List *joinquals;
ListCell *l;
/*
* In an ANTI join, we must ignore clauses that are "pushed down", since
* those won't affect the match logic. In a SEMI join, we do not
* distinguish joinquals from "pushed down" quals, so just use the whole
* restrictinfo list. For other outer join types, we should consider only
* non-pushed-down quals, so that this devolves to an IS_OUTER_JOIN check.
*/
if (IS_OUTER_JOIN(jointype))
{
joinquals = NIL;
foreach(l, restrictlist)
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, l);
if (!RINFO_IS_PUSHED_DOWN(rinfo, joinrel->relids))
joinquals = lappend(joinquals, rinfo);
}
}
else
joinquals = restrictlist;
/*
* Get the JOIN_SEMI or JOIN_ANTI selectivity of the join clauses.
*/
jselec = clauselist_selectivity(root,
joinquals,
0,
(jointype == JOIN_ANTI) ? JOIN_ANTI : JOIN_SEMI,
sjinfo);
/*
* Also get the normal inner-join selectivity of the join clauses.
*/
norm_sjinfo.type = T_SpecialJoinInfo;
norm_sjinfo.min_lefthand = outerrel->relids;
norm_sjinfo.min_righthand = innerrel->relids;
norm_sjinfo.syn_lefthand = outerrel->relids;
norm_sjinfo.syn_righthand = innerrel->relids;
norm_sjinfo.jointype = JOIN_INNER;
/* we don't bother trying to make the remaining fields valid */
norm_sjinfo.lhs_strict = false;
norm_sjinfo.delay_upper_joins = false;
norm_sjinfo.semi_can_btree = false;
norm_sjinfo.semi_can_hash = false;
norm_sjinfo.semi_operators = NIL;
norm_sjinfo.semi_rhs_exprs = NIL;
nselec = clauselist_selectivity(root,
joinquals,
0,
JOIN_INNER,
&norm_sjinfo);
/* Avoid leaking a lot of ListCells */
if (IS_OUTER_JOIN(jointype))
list_free(joinquals);
/*
* jselec can be interpreted as the fraction of outer-rel rows that have
* any matches (this is true for both SEMI and ANTI cases). And nselec is
* the fraction of the Cartesian product that matches. So, the average
* number of matches for each outer-rel row that has at least one match is
* nselec * inner_rows / jselec.
*
* Note: it is correct to use the inner rel's "rows" count here, even
* though we might later be considering a parameterized inner path with
* fewer rows. This is because we have included all the join clauses in
* the selectivity estimate.
*/
if (jselec > 0) /* protect against zero divide */
{
avgmatch = nselec * innerrel->rows / jselec;
/* Clamp to sane range */
avgmatch = Max(1.0, avgmatch);
}
else
avgmatch = 1.0;
semifactors->outer_match_frac = jselec;
semifactors->match_count = avgmatch;
}
/*
* has_indexed_join_quals
* Check whether all the joinquals of a nestloop join are used as
* inner index quals.
*
* If the inner path of a SEMI/ANTI join is an indexscan (including bitmap
* indexscan) that uses all the joinquals as indexquals, we can assume that an
* unmatched outer tuple is cheap to process, whereas otherwise it's probably
* expensive.
*/
static bool
has_indexed_join_quals(NestPath *joinpath)
{
Relids joinrelids = joinpath->path.parent->relids;
Path *innerpath = joinpath->innerjoinpath;
List *indexclauses;
bool found_one;
ListCell *lc;
/* If join still has quals to evaluate, it's not fast */
if (joinpath->joinrestrictinfo != NIL)
return false;
/* Nor if the inner path isn't parameterized at all */
if (innerpath->param_info == NULL)
return false;
/* Find the indexclauses list for the inner scan */
switch (innerpath->pathtype)
{
case T_IndexScan:
case T_IndexOnlyScan:
indexclauses = ((IndexPath *) innerpath)->indexclauses;
break;
case T_BitmapHeapScan:
{
/* Accept only a simple bitmap scan, not AND/OR cases */
Path *bmqual = ((BitmapHeapPath *) innerpath)->bitmapqual;
if (IsA(bmqual, IndexPath))
indexclauses = ((IndexPath *) bmqual)->indexclauses;
else
return false;
break;
}
default:
/*
* If it's not a simple indexscan, it probably doesn't run quickly
* for zero rows out, even if it's a parameterized path using all
* the joinquals.
*/
return false;
}
/*
* Examine the inner path's param clauses. Any that are from the outer
* path must be found in the indexclauses list, either exactly or in an
* equivalent form generated by equivclass.c. Also, we must find at least
* one such clause, else it's a clauseless join which isn't fast.
*/
found_one = false;
foreach(lc, innerpath->param_info->ppi_clauses)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
if (join_clause_is_movable_into(rinfo,
innerpath->parent->relids,
joinrelids))
{
if (!is_redundant_with_indexclauses(rinfo, indexclauses))
return false;
found_one = true;
}
}
return found_one;
}
/*
* approx_tuple_count
* Quick-and-dirty estimation of the number of join rows passing
* a set of qual conditions.
*
* The quals can be either an implicitly-ANDed list of boolean expressions,
* or a list of RestrictInfo nodes (typically the latter).
*
* We intentionally compute the selectivity under JOIN_INNER rules, even
* if it's some type of outer join. This is appropriate because we are
* trying to figure out how many tuples pass the initial merge or hash
* join step.
*
* This is quick-and-dirty because we bypass clauselist_selectivity, and
* simply multiply the independent clause selectivities together. Now
* clauselist_selectivity often can't do any better than that anyhow, but
* for some situations (such as range constraints) it is smarter. However,
* we can't effectively cache the results of clauselist_selectivity, whereas
* the individual clause selectivities can be and are cached.
*
* Since we are only using the results to estimate how many potential
* output tuples are generated and passed through qpqual checking, it
* seems OK to live with the approximation.
*/
static double
approx_tuple_count(PlannerInfo *root, JoinPath *path, List *quals)
{
double tuples;
double outer_tuples = path->outerjoinpath->rows;
double inner_tuples = path->innerjoinpath->rows;
SpecialJoinInfo sjinfo;
Selectivity selec = 1.0;
ListCell *l;
/*
* Make up a SpecialJoinInfo for JOIN_INNER semantics.
*/
sjinfo.type = T_SpecialJoinInfo;
sjinfo.min_lefthand = path->outerjoinpath->parent->relids;
sjinfo.min_righthand = path->innerjoinpath->parent->relids;
sjinfo.syn_lefthand = path->outerjoinpath->parent->relids;
sjinfo.syn_righthand = path->innerjoinpath->parent->relids;
sjinfo.jointype = JOIN_INNER;
/* we don't bother trying to make the remaining fields valid */
sjinfo.lhs_strict = false;
sjinfo.delay_upper_joins = false;
sjinfo.semi_can_btree = false;
sjinfo.semi_can_hash = false;
sjinfo.semi_operators = NIL;
sjinfo.semi_rhs_exprs = NIL;
/* Get the approximate selectivity */
foreach(l, quals)
{
Node *qual = (Node *) lfirst(l);
/* Note that clause_selectivity will be able to cache its result */
selec *= clause_selectivity(root, qual, 0, JOIN_INNER, &sjinfo);
}
/* Apply it to the input relation sizes */
tuples = selec * outer_tuples * inner_tuples;
return clamp_row_est(tuples);
}
/*
* set_baserel_size_estimates
* Set the size estimates for the given base relation.
*
* The rel's targetlist and restrictinfo list must have been constructed
* already, and rel->tuples must be set.
*
* We set the following fields of the rel node:
* rows: the estimated number of output tuples (after applying
* restriction clauses).
* width: the estimated average output tuple width in bytes.
* baserestrictcost: estimated cost of evaluating baserestrictinfo clauses.
*/
void
set_baserel_size_estimates(PlannerInfo *root, RelOptInfo *rel)
{
double nrows;
/* Should only be applied to base relations */
Assert(rel->relid > 0);
nrows = rel->tuples *
clauselist_selectivity(root,
rel->baserestrictinfo,
0,
JOIN_INNER,
NULL);
rel->rows = clamp_row_est(nrows);
cost_qual_eval(&rel->baserestrictcost, rel->baserestrictinfo, root);
set_rel_width(root, rel);
}
/*
* get_parameterized_baserel_size
* Make a size estimate for a parameterized scan of a base relation.
*
* 'param_clauses' lists the additional join clauses to be used.
*
* set_baserel_size_estimates must have been applied already.
*/
double
get_parameterized_baserel_size(PlannerInfo *root, RelOptInfo *rel,
List *param_clauses)
{
List *allclauses;
double nrows;
/*
* Estimate the number of rows returned by the parameterized scan, knowing
* that it will apply all the extra join clauses as well as the rel's own
* restriction clauses. Note that we force the clauses to be treated as
* non-join clauses during selectivity estimation.
*/
allclauses = list_concat_copy(param_clauses, rel->baserestrictinfo);
nrows = rel->tuples *
clauselist_selectivity(root,
allclauses,
rel->relid, /* do not use 0! */
JOIN_INNER,
NULL);
nrows = clamp_row_est(nrows);
/* For safety, make sure result is not more than the base estimate */
if (nrows > rel->rows)
nrows = rel->rows;
return nrows;
}
/*
* set_joinrel_size_estimates
* Set the size estimates for the given join relation.
*
* The rel's targetlist must have been constructed already, and a
* restriction clause list that matches the given component rels must
* be provided.
*
* Since there is more than one way to make a joinrel for more than two
* base relations, the results we get here could depend on which component
* rel pair is provided. In theory we should get the same answers no matter
* which pair is provided; in practice, since the selectivity estimation
* routines don't handle all cases equally well, we might not. But there's
* not much to be done about it. (Would it make sense to repeat the
* calculations for each pair of input rels that's encountered, and somehow
* average the results? Probably way more trouble than it's worth, and
* anyway we must keep the rowcount estimate the same for all paths for the
* joinrel.)
*
* We set only the rows field here. The reltarget field was already set by
* build_joinrel_tlist, and baserestrictcost is not used for join rels.
*/
void
set_joinrel_size_estimates(PlannerInfo *root, RelOptInfo *rel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel,
SpecialJoinInfo *sjinfo,
List *restrictlist)
{
rel->rows = calc_joinrel_size_estimate(root,
rel,
outer_rel,
inner_rel,
outer_rel->rows,
inner_rel->rows,
sjinfo,
restrictlist);
}
/*
* get_parameterized_joinrel_size
* Make a size estimate for a parameterized scan of a join relation.
*
* 'rel' is the joinrel under consideration.
* 'outer_path', 'inner_path' are (probably also parameterized) Paths that
* produce the relations being joined.
* 'sjinfo' is any SpecialJoinInfo relevant to this join.
* 'restrict_clauses' lists the join clauses that need to be applied at the
* join node (including any movable clauses that were moved down to this join,
* and not including any movable clauses that were pushed down into the
* child paths).
*
* set_joinrel_size_estimates must have been applied already.
*/
double
get_parameterized_joinrel_size(PlannerInfo *root, RelOptInfo *rel,
Path *outer_path,
Path *inner_path,
SpecialJoinInfo *sjinfo,
List *restrict_clauses)
{
double nrows;
/*
* Estimate the number of rows returned by the parameterized join as the
* sizes of the input paths times the selectivity of the clauses that have
* ended up at this join node.
*
* As with set_joinrel_size_estimates, the rowcount estimate could depend
* on the pair of input paths provided, though ideally we'd get the same
* estimate for any pair with the same parameterization.
*/
nrows = calc_joinrel_size_estimate(root,
rel,
outer_path->parent,
inner_path->parent,
outer_path->rows,
inner_path->rows,
sjinfo,
restrict_clauses);
/* For safety, make sure result is not more than the base estimate */
if (nrows > rel->rows)
nrows = rel->rows;
return nrows;
}
/*
* calc_joinrel_size_estimate
* Workhorse for set_joinrel_size_estimates and
* get_parameterized_joinrel_size.
*
* outer_rel/inner_rel are the relations being joined, but they should be
* assumed to have sizes outer_rows/inner_rows; those numbers might be less
* than what rel->rows says, when we are considering parameterized paths.
*/
static double
calc_joinrel_size_estimate(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel,
double outer_rows,
double inner_rows,
SpecialJoinInfo *sjinfo,
List *restrictlist_in)
{
/* This apparently-useless variable dodges a compiler bug in VS2013: */
List *restrictlist = restrictlist_in;
JoinType jointype = sjinfo->jointype;
Selectivity fkselec;
Selectivity jselec;
Selectivity pselec;
double nrows;
/*
* Compute joinclause selectivity. Note that we are only considering
* clauses that become restriction clauses at this join level; we are not
* double-counting them because they were not considered in estimating the
* sizes of the component rels.
*
* First, see whether any of the joinclauses can be matched to known FK
* constraints. If so, drop those clauses from the restrictlist, and
* instead estimate their selectivity using FK semantics. (We do this
* without regard to whether said clauses are local or "pushed down".
* Probably, an FK-matching clause could never be seen as pushed down at
* an outer join, since it would be strict and hence would be grounds for
* join strength reduction.) fkselec gets the net selectivity for
* FK-matching clauses, or 1.0 if there are none.
*/
fkselec = get_foreign_key_join_selectivity(root,
outer_rel->relids,
inner_rel->relids,
sjinfo,
&restrictlist);
/*
* For an outer join, we have to distinguish the selectivity of the join's
* own clauses (JOIN/ON conditions) from any clauses that were "pushed
* down". For inner joins we just count them all as joinclauses.
*/
if (IS_OUTER_JOIN(jointype))
{
List *joinquals = NIL;
List *pushedquals = NIL;
ListCell *l;
/* Grovel through the clauses to separate into two lists */
foreach(l, restrictlist)
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, l);
if (RINFO_IS_PUSHED_DOWN(rinfo, joinrel->relids))
pushedquals = lappend(pushedquals, rinfo);
else
joinquals = lappend(joinquals, rinfo);
}
/* Get the separate selectivities */
jselec = clauselist_selectivity(root,
joinquals,
0,
jointype,
sjinfo);
pselec = clauselist_selectivity(root,
pushedquals,
0,
jointype,
sjinfo);
/* Avoid leaking a lot of ListCells */
list_free(joinquals);
list_free(pushedquals);
}
else
{
jselec = clauselist_selectivity(root,
restrictlist,
0,
jointype,
sjinfo);
pselec = 0.0; /* not used, keep compiler quiet */
}
/*
* Basically, we multiply size of Cartesian product by selectivity.
*
* If we are doing an outer join, take that into account: the joinqual
* selectivity has to be clamped using the knowledge that the output must
* be at least as large as the non-nullable input. However, any
* pushed-down quals are applied after the outer join, so their
* selectivity applies fully.
*
* For JOIN_SEMI and JOIN_ANTI, the selectivity is defined as the fraction
* of LHS rows that have matches, and we apply that straightforwardly.
*/
switch (jointype)
{
case JOIN_INNER:
nrows = outer_rows * inner_rows * fkselec * jselec;
/* pselec not used */
break;
case JOIN_LEFT:
nrows = outer_rows * inner_rows * fkselec * jselec;
if (nrows < outer_rows)
nrows = outer_rows;
nrows *= pselec;
break;
case JOIN_FULL:
nrows = outer_rows * inner_rows * fkselec * jselec;
if (nrows < outer_rows)
nrows = outer_rows;
if (nrows < inner_rows)
nrows = inner_rows;
nrows *= pselec;
break;
case JOIN_SEMI:
nrows = outer_rows * fkselec * jselec;
/* pselec not used */
break;
case JOIN_ANTI:
nrows = outer_rows * (1.0 - fkselec * jselec);
nrows *= pselec;
break;
default:
/* other values not expected here */
elog(ERROR, "unrecognized join type: %d", (int) jointype);
nrows = 0; /* keep compiler quiet */
break;
}
return clamp_row_est(nrows);
}
/*
* get_foreign_key_join_selectivity
* Estimate join selectivity for foreign-key-related clauses.
*
* Remove any clauses that can be matched to FK constraints from *restrictlist,
* and return a substitute estimate of their selectivity. 1.0 is returned
* when there are no such clauses.
*
* The reason for treating such clauses specially is that we can get better
* estimates this way than by relying on clauselist_selectivity(), especially
* for multi-column FKs where that function's assumption that the clauses are
* independent falls down badly. But even with single-column FKs, we may be
* able to get a better answer when the pg_statistic stats are missing or out
* of date.
*/
static Selectivity
get_foreign_key_join_selectivity(PlannerInfo *root,
Relids outer_relids,
Relids inner_relids,
SpecialJoinInfo *sjinfo,
List **restrictlist)
{
Selectivity fkselec = 1.0;
JoinType jointype = sjinfo->jointype;
List *worklist = *restrictlist;
ListCell *lc;
/* Consider each FK constraint that is known to match the query */
foreach(lc, root->fkey_list)
{
ForeignKeyOptInfo *fkinfo = (ForeignKeyOptInfo *) lfirst(lc);
bool ref_is_outer;
List *removedlist;
ListCell *cell;
/*
* This FK is not relevant unless it connects a baserel on one side of
* this join to a baserel on the other side.
*/
if (bms_is_member(fkinfo->con_relid, outer_relids) &&
bms_is_member(fkinfo->ref_relid, inner_relids))
ref_is_outer = false;
else if (bms_is_member(fkinfo->ref_relid, outer_relids) &&
bms_is_member(fkinfo->con_relid, inner_relids))
ref_is_outer = true;
else
continue;
/*
* If we're dealing with a semi/anti join, and the FK's referenced
* relation is on the outside, then knowledge of the FK doesn't help
* us figure out what we need to know (which is the fraction of outer
* rows that have matches). On the other hand, if the referenced rel
* is on the inside, then all outer rows must have matches in the
* referenced table (ignoring nulls). But any restriction or join
* clauses that filter that table will reduce the fraction of matches.
* We can account for restriction clauses, but it's too hard to guess
* how many table rows would get through a join that's inside the RHS.
* Hence, if either case applies, punt and ignore the FK.
*/
if ((jointype == JOIN_SEMI || jointype == JOIN_ANTI) &&
(ref_is_outer || bms_membership(inner_relids) != BMS_SINGLETON))
continue;
/*
* Modify the restrictlist by removing clauses that match the FK (and
* putting them into removedlist instead). It seems unsafe to modify
* the originally-passed List structure, so we make a shallow copy the
* first time through.
*/
if (worklist == *restrictlist)
worklist = list_copy(worklist);
removedlist = NIL;
foreach(cell, worklist)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
bool remove_it = false;
int i;
/* Drop this clause if it matches any column of the FK */
for (i = 0; i < fkinfo->nkeys; i++)
{
if (rinfo->parent_ec)
{
/*
* EC-derived clauses can only match by EC. It is okay to
* consider any clause derived from the same EC as
* matching the FK: even if equivclass.c chose to generate
* a clause equating some other pair of Vars, it could
* have generated one equating the FK's Vars. So for
* purposes of estimation, we can act as though it did so.
*
* Note: checking parent_ec is a bit of a cheat because
* there are EC-derived clauses that don't have parent_ec
* set; but such clauses must compare expressions that
* aren't just Vars, so they cannot match the FK anyway.
*/
if (fkinfo->eclass[i] == rinfo->parent_ec)
{
remove_it = true;
break;
}
}
else
{
/*
* Otherwise, see if rinfo was previously matched to FK as
* a "loose" clause.
*/
if (list_member_ptr(fkinfo->rinfos[i], rinfo))
{
remove_it = true;
break;
}
}
}
if (remove_it)
{
worklist = foreach_delete_current(worklist, cell);
removedlist = lappend(removedlist, rinfo);
}
}
/*
* If we failed to remove all the matching clauses we expected to
* find, chicken out and ignore this FK; applying its selectivity
* might result in double-counting. Put any clauses we did manage to
* remove back into the worklist.
*
* Since the matching clauses are known not outerjoin-delayed, they
* should certainly have appeared in the initial joinclause list. If
* we didn't find them, they must have been matched to, and removed
* by, some other FK in a previous iteration of this loop. (A likely
* case is that two FKs are matched to the same EC; there will be only
* one EC-derived clause in the initial list, so the first FK will
* consume it.) Applying both FKs' selectivity independently risks
* underestimating the join size; in particular, this would undo one
* of the main things that ECs were invented for, namely to avoid
* double-counting the selectivity of redundant equality conditions.
* Later we might think of a reasonable way to combine the estimates,
* but for now, just punt, since this is a fairly uncommon situation.
*/
if (list_length(removedlist) !=
(fkinfo->nmatched_ec + fkinfo->nmatched_ri))
{
worklist = list_concat(worklist, removedlist);
continue;
}
/*
* Finally we get to the payoff: estimate selectivity using the
* knowledge that each referencing row will match exactly one row in
* the referenced table.
*
* XXX that's not true in the presence of nulls in the referencing
* column(s), so in principle we should derate the estimate for those.
* However (1) if there are any strict restriction clauses for the
* referencing column(s) elsewhere in the query, derating here would
* be double-counting the null fraction, and (2) it's not very clear
* how to combine null fractions for multiple referencing columns. So
* we do nothing for now about correcting for nulls.
*
* XXX another point here is that if either side of an FK constraint
* is an inheritance parent, we estimate as though the constraint
* covers all its children as well. This is not an unreasonable
* assumption for a referencing table, ie the user probably applied
* identical constraints to all child tables (though perhaps we ought
* to check that). But it's not possible to have done that for a
* referenced table. Fortunately, precisely because that doesn't
* work, it is uncommon in practice to have an FK referencing a parent
* table. So, at least for now, disregard inheritance here.
*/
if (jointype == JOIN_SEMI || jointype == JOIN_ANTI)
{
/*
* For JOIN_SEMI and JOIN_ANTI, we only get here when the FK's
* referenced table is exactly the inside of the join. The join
* selectivity is defined as the fraction of LHS rows that have
* matches. The FK implies that every LHS row has a match *in the
* referenced table*; but any restriction clauses on it will
* reduce the number of matches. Hence we take the join
* selectivity as equal to the selectivity of the table's
* restriction clauses, which is rows / tuples; but we must guard
* against tuples == 0.
*/
RelOptInfo *ref_rel = find_base_rel(root, fkinfo->ref_relid);
double ref_tuples = Max(ref_rel->tuples, 1.0);
fkselec *= ref_rel->rows / ref_tuples;
}
else
{
/*
* Otherwise, selectivity is exactly 1/referenced-table-size; but
* guard against tuples == 0. Note we should use the raw table
* tuple count, not any estimate of its filtered or joined size.
*/
RelOptInfo *ref_rel = find_base_rel(root, fkinfo->ref_relid);
double ref_tuples = Max(ref_rel->tuples, 1.0);
fkselec *= 1.0 / ref_tuples;
}
}
*restrictlist = worklist;
return fkselec;
}
/*
* set_subquery_size_estimates
* Set the size estimates for a base relation that is a subquery.
*
* The rel's targetlist and restrictinfo list must have been constructed
* already, and the Paths for the subquery must have been completed.
* We look at the subquery's PlannerInfo to extract data.
*
* We set the same fields as set_baserel_size_estimates.
*/
void
set_subquery_size_estimates(PlannerInfo *root, RelOptInfo *rel)
{
PlannerInfo *subroot = rel->subroot;
RelOptInfo *sub_final_rel;
ListCell *lc;
/* Should only be applied to base relations that are subqueries */
Assert(rel->relid > 0);
Assert(planner_rt_fetch(rel->relid, root)->rtekind == RTE_SUBQUERY);
/*
* Copy raw number of output rows from subquery. All of its paths should
* have the same output rowcount, so just look at cheapest-total.
*/
sub_final_rel = fetch_upper_rel(subroot, UPPERREL_FINAL, NULL);
rel->tuples = sub_final_rel->cheapest_total_path->rows;
/*
* Compute per-output-column width estimates by examining the subquery's
* targetlist. For any output that is a plain Var, get the width estimate
* that was made while planning the subquery. Otherwise, we leave it to
* set_rel_width to fill in a datatype-based default estimate.
*/
foreach(lc, subroot->parse->targetList)
{
TargetEntry *te = lfirst_node(TargetEntry, lc);
Node *texpr = (Node *) te->expr;
int32 item_width = 0;
/* junk columns aren't visible to upper query */
if (te->resjunk)
continue;
/*
* The subquery could be an expansion of a view that's had columns
* added to it since the current query was parsed, so that there are
* non-junk tlist columns in it that don't correspond to any column
* visible at our query level. Ignore such columns.
*/
if (te->resno < rel->min_attr || te->resno > rel->max_attr)
continue;
/*
* XXX This currently doesn't work for subqueries containing set
* operations, because the Vars in their tlists are bogus references
* to the first leaf subquery, which wouldn't give the right answer
* even if we could still get to its PlannerInfo.
*
* Also, the subquery could be an appendrel for which all branches are
* known empty due to constraint exclusion, in which case
* set_append_rel_pathlist will have left the attr_widths set to zero.
*
* In either case, we just leave the width estimate zero until
* set_rel_width fixes it.
*/
if (IsA(texpr, Var) &&
subroot->parse->setOperations == NULL)
{
Var *var = (Var *) texpr;
RelOptInfo *subrel = find_base_rel(subroot, var->varno);
item_width = subrel->attr_widths[var->varattno - subrel->min_attr];
}
rel->attr_widths[te->resno - rel->min_attr] = item_width;
}
/* Now estimate number of output rows, etc */
set_baserel_size_estimates(root, rel);
}
/*
* set_function_size_estimates
* Set the size estimates for a base relation that is a function call.
*
* The rel's targetlist and restrictinfo list must have been constructed
* already.
*
* We set the same fields as set_baserel_size_estimates.
*/
void
set_function_size_estimates(PlannerInfo *root, RelOptInfo *rel)
{
RangeTblEntry *rte;
ListCell *lc;
/* Should only be applied to base relations that are functions */
Assert(rel->relid > 0);
rte = planner_rt_fetch(rel->relid, root);
Assert(rte->rtekind == RTE_FUNCTION);
/*
* Estimate number of rows the functions will return. The rowcount of the
* node is that of the largest function result.
*/
rel->tuples = 0;
foreach(lc, rte->functions)
{
RangeTblFunction *rtfunc = (RangeTblFunction *) lfirst(lc);
double ntup = expression_returns_set_rows(root, rtfunc->funcexpr);
if (ntup > rel->tuples)
rel->tuples = ntup;
}
/* Now estimate number of output rows, etc */
set_baserel_size_estimates(root, rel);
}
/*
* set_function_size_estimates
* Set the size estimates for a base relation that is a function call.
*
* The rel's targetlist and restrictinfo list must have been constructed
* already.
*
* We set the same fields as set_tablefunc_size_estimates.
*/
void
set_tablefunc_size_estimates(PlannerInfo *root, RelOptInfo *rel)
{
/* Should only be applied to base relations that are functions */
Assert(rel->relid > 0);
Assert(planner_rt_fetch(rel->relid, root)->rtekind == RTE_TABLEFUNC);
rel->tuples = 100;
/* Now estimate number of output rows, etc */
set_baserel_size_estimates(root, rel);
}
/*
* set_values_size_estimates
* Set the size estimates for a base relation that is a values list.
*
* The rel's targetlist and restrictinfo list must have been constructed
* already.
*
* We set the same fields as set_baserel_size_estimates.
*/
void
set_values_size_estimates(PlannerInfo *root, RelOptInfo *rel)
{
RangeTblEntry *rte;
/* Should only be applied to base relations that are values lists */
Assert(rel->relid > 0);
rte = planner_rt_fetch(rel->relid, root);
Assert(rte->rtekind == RTE_VALUES);
/*
* Estimate number of rows the values list will return. We know this
* precisely based on the list length (well, barring set-returning
* functions in list items, but that's a refinement not catered for
* anywhere else either).
*/
rel->tuples = list_length(rte->values_lists);
/* Now estimate number of output rows, etc */
set_baserel_size_estimates(root, rel);
}
/*
* set_cte_size_estimates
* Set the size estimates for a base relation that is a CTE reference.
*
* The rel's targetlist and restrictinfo list must have been constructed
* already, and we need an estimate of the number of rows returned by the CTE
* (if a regular CTE) or the non-recursive term (if a self-reference).
*
* We set the same fields as set_baserel_size_estimates.
*/
void
set_cte_size_estimates(PlannerInfo *root, RelOptInfo *rel, double cte_rows)
{
RangeTblEntry *rte;
/* Should only be applied to base relations that are CTE references */
Assert(rel->relid > 0);
rte = planner_rt_fetch(rel->relid, root);
Assert(rte->rtekind == RTE_CTE);
if (rte->self_reference)
{
/*
* In a self-reference, arbitrarily assume the average worktable size
* is about 10 times the nonrecursive term's size.
*/
rel->tuples = 10 * cte_rows;
}
else
{
/* Otherwise just believe the CTE's rowcount estimate */
rel->tuples = cte_rows;
}
/* Now estimate number of output rows, etc */
set_baserel_size_estimates(root, rel);
}
/*
* set_namedtuplestore_size_estimates
* Set the size estimates for a base relation that is a tuplestore reference.
*
* The rel's targetlist and restrictinfo list must have been constructed
* already.
*
* We set the same fields as set_baserel_size_estimates.
*/
void
set_namedtuplestore_size_estimates(PlannerInfo *root, RelOptInfo *rel)
{
RangeTblEntry *rte;
/* Should only be applied to base relations that are tuplestore references */
Assert(rel->relid > 0);
rte = planner_rt_fetch(rel->relid, root);
Assert(rte->rtekind == RTE_NAMEDTUPLESTORE);
/*
* Use the estimate provided by the code which is generating the named
* tuplestore. In some cases, the actual number might be available; in
* others the same plan will be re-used, so a "typical" value might be
* estimated and used.
*/
rel->tuples = rte->enrtuples;
if (rel->tuples < 0)
rel->tuples = 1000;
/* Now estimate number of output rows, etc */
set_baserel_size_estimates(root, rel);
}
/*
* set_result_size_estimates
* Set the size estimates for an RTE_RESULT base relation
*
* The rel's targetlist and restrictinfo list must have been constructed
* already.
*
* We set the same fields as set_baserel_size_estimates.
*/
void
set_result_size_estimates(PlannerInfo *root, RelOptInfo *rel)
{
/* Should only be applied to RTE_RESULT base relations */
Assert(rel->relid > 0);
Assert(planner_rt_fetch(rel->relid, root)->rtekind == RTE_RESULT);
/* RTE_RESULT always generates a single row, natively */
rel->tuples = 1;
/* Now estimate number of output rows, etc */
set_baserel_size_estimates(root, rel);
}
/*
* set_foreign_size_estimates
* Set the size estimates for a base relation that is a foreign table.
*
* There is not a whole lot that we can do here; the foreign-data wrapper
* is responsible for producing useful estimates. We can do a decent job
* of estimating baserestrictcost, so we set that, and we also set up width
* using what will be purely datatype-driven estimates from the targetlist.
* There is no way to do anything sane with the rows value, so we just put
* a default estimate and hope that the wrapper can improve on it. The
* wrapper's GetForeignRelSize function will be called momentarily.
*
* The rel's targetlist and restrictinfo list must have been constructed
* already.
*/
void
set_foreign_size_estimates(PlannerInfo *root, RelOptInfo *rel)
{
/* Should only be applied to base relations */
Assert(rel->relid > 0);
rel->rows = 1000; /* entirely bogus default estimate */
cost_qual_eval(&rel->baserestrictcost, rel->baserestrictinfo, root);
set_rel_width(root, rel);
}
/*
* set_rel_width
* Set the estimated output width of a base relation.
*
* The estimated output width is the sum of the per-attribute width estimates
* for the actually-referenced columns, plus any PHVs or other expressions
* that have to be calculated at this relation. This is the amount of data
* we'd need to pass upwards in case of a sort, hash, etc.
*
* This function also sets reltarget->cost, so it's a bit misnamed now.
*
* NB: this works best on plain relations because it prefers to look at
* real Vars. For subqueries, set_subquery_size_estimates will already have
* copied up whatever per-column estimates were made within the subquery,
* and for other types of rels there isn't much we can do anyway. We fall
* back on (fairly stupid) datatype-based width estimates if we can't get
* any better number.
*
* The per-attribute width estimates are cached for possible re-use while
* building join relations or post-scan/join pathtargets.
*/
static void
set_rel_width(PlannerInfo *root, RelOptInfo *rel)
{
Oid reloid = planner_rt_fetch(rel->relid, root)->relid;
int32 tuple_width = 0;
bool have_wholerow_var = false;
ListCell *lc;
/* Vars are assumed to have cost zero, but other exprs do not */
rel->reltarget->cost.startup = 0;
rel->reltarget->cost.per_tuple = 0;
foreach(lc, rel->reltarget->exprs)
{
Node *node = (Node *) lfirst(lc);
/*
* Ordinarily, a Var in a rel's targetlist must belong to that rel;
* but there are corner cases involving LATERAL references where that
* isn't so. If the Var has the wrong varno, fall through to the
* generic case (it doesn't seem worth the trouble to be any smarter).
*/
if (IsA(node, Var) &&
((Var *) node)->varno == rel->relid)
{
Var *var = (Var *) node;
int ndx;
int32 item_width;
Assert(var->varattno >= rel->min_attr);
Assert(var->varattno <= rel->max_attr);
ndx = var->varattno - rel->min_attr;
/*
* If it's a whole-row Var, we'll deal with it below after we have
* already cached as many attr widths as possible.
*/
if (var->varattno == 0)
{
have_wholerow_var = true;
continue;
}
/*
* The width may have been cached already (especially if it's a
* subquery), so don't duplicate effort.
*/
if (rel->attr_widths[ndx] > 0)
{
tuple_width += rel->attr_widths[ndx];
continue;
}
/* Try to get column width from statistics */
if (reloid != InvalidOid && var->varattno > 0)
{
item_width = get_attavgwidth(reloid, var->varattno);
if (item_width > 0)
{
rel->attr_widths[ndx] = item_width;
tuple_width += item_width;
continue;
}
}
/*
* Not a plain relation, or can't find statistics for it. Estimate
* using just the type info.
*/
item_width = get_typavgwidth(var->vartype, var->vartypmod);
Assert(item_width > 0);
rel->attr_widths[ndx] = item_width;
tuple_width += item_width;
}
else if (IsA(node, PlaceHolderVar))
{
/*
* We will need to evaluate the PHV's contained expression while
* scanning this rel, so be sure to include it in reltarget->cost.
*/
PlaceHolderVar *phv = (PlaceHolderVar *) node;
PlaceHolderInfo *phinfo = find_placeholder_info(root, phv, false);
QualCost cost;
tuple_width += phinfo->ph_width;
cost_qual_eval_node(&cost, (Node *) phv->phexpr, root);
rel->reltarget->cost.startup += cost.startup;
rel->reltarget->cost.per_tuple += cost.per_tuple;
}
else
{
/*
* We could be looking at an expression pulled up from a subquery,
* or a ROW() representing a whole-row child Var, etc. Do what we
* can using the expression type information.
*/
int32 item_width;
QualCost cost;
item_width = get_typavgwidth(exprType(node), exprTypmod(node));
Assert(item_width > 0);
tuple_width += item_width;
/* Not entirely clear if we need to account for cost, but do so */
cost_qual_eval_node(&cost, node, root);
rel->reltarget->cost.startup += cost.startup;
rel->reltarget->cost.per_tuple += cost.per_tuple;
}
}
/*
* If we have a whole-row reference, estimate its width as the sum of
* per-column widths plus heap tuple header overhead.
*/
if (have_wholerow_var)
{
int32 wholerow_width = MAXALIGN(SizeofHeapTupleHeader);
if (reloid != InvalidOid)
{
/* Real relation, so estimate true tuple width */
wholerow_width += get_relation_data_width(reloid,
rel->attr_widths - rel->min_attr);
}
else
{
/* Do what we can with info for a phony rel */
AttrNumber i;
for (i = 1; i <= rel->max_attr; i++)
wholerow_width += rel->attr_widths[i - rel->min_attr];
}
rel->attr_widths[0 - rel->min_attr] = wholerow_width;
/*
* Include the whole-row Var as part of the output tuple. Yes, that
* really is what happens at runtime.
*/
tuple_width += wholerow_width;
}
Assert(tuple_width >= 0);
rel->reltarget->width = tuple_width;
}
/*
* set_pathtarget_cost_width
* Set the estimated eval cost and output width of a PathTarget tlist.
*
* As a notational convenience, returns the same PathTarget pointer passed in.
*
* Most, though not quite all, uses of this function occur after we've run
* set_rel_width() for base relations; so we can usually obtain cached width
* estimates for Vars. If we can't, fall back on datatype-based width
* estimates. Present early-planning uses of PathTargets don't need accurate
* widths badly enough to justify going to the catalogs for better data.
*/
PathTarget *
set_pathtarget_cost_width(PlannerInfo *root, PathTarget *target)
{
int32 tuple_width = 0;
ListCell *lc;
/* Vars are assumed to have cost zero, but other exprs do not */
target->cost.startup = 0;
target->cost.per_tuple = 0;
foreach(lc, target->exprs)
{
Node *node = (Node *) lfirst(lc);
if (IsA(node, Var))
{
Var *var = (Var *) node;
int32 item_width;
/* We should not see any upper-level Vars here */
Assert(var->varlevelsup == 0);
/* Try to get data from RelOptInfo cache */
if (var->varno < root->simple_rel_array_size)
{
RelOptInfo *rel = root->simple_rel_array[var->varno];
if (rel != NULL &&
var->varattno >= rel->min_attr &&
var->varattno <= rel->max_attr)
{
int ndx = var->varattno - rel->min_attr;
if (rel->attr_widths[ndx] > 0)
{
tuple_width += rel->attr_widths[ndx];
continue;
}
}
}
/*
* No cached data available, so estimate using just the type info.
*/
item_width = get_typavgwidth(var->vartype, var->vartypmod);
Assert(item_width > 0);
tuple_width += item_width;
}
else
{
/*
* Handle general expressions using type info.
*/
int32 item_width;
QualCost cost;
item_width = get_typavgwidth(exprType(node), exprTypmod(node));
Assert(item_width > 0);
tuple_width += item_width;
/* Account for cost, too */
cost_qual_eval_node(&cost, node, root);
target->cost.startup += cost.startup;
target->cost.per_tuple += cost.per_tuple;
}
}
Assert(tuple_width >= 0);
target->width = tuple_width;
return target;
}
/*
* relation_byte_size
* Estimate the storage space in bytes for a given number of tuples
* of a given width (size in bytes).
*/
static double
relation_byte_size(double tuples, int width)
{
return tuples * (MAXALIGN(width) + MAXALIGN(SizeofHeapTupleHeader));
}
/*
* page_size
* Returns an estimate of the number of pages covered by a given
* number of tuples of a given width (size in bytes).
*/
static double
page_size(double tuples, int width)
{
return ceil(relation_byte_size(tuples, width) / BLCKSZ);
}
/*
* Estimate the fraction of the work that each worker will do given the
* number of workers budgeted for the path.
*/
static double
get_parallel_divisor(Path *path)
{
double parallel_divisor = path->parallel_workers;
/*
* Early experience with parallel query suggests that when there is only
* one worker, the leader often makes a very substantial contribution to
* executing the parallel portion of the plan, but as more workers are
* added, it does less and less, because it's busy reading tuples from the
* workers and doing whatever non-parallel post-processing is needed. By
* the time we reach 4 workers, the leader no longer makes a meaningful
* contribution. Thus, for now, estimate that the leader spends 30% of
* its time servicing each worker, and the remainder executing the
* parallel plan.
*/
if (parallel_leader_participation)
{
double leader_contribution;
leader_contribution = 1.0 - (0.3 * path->parallel_workers);
if (leader_contribution > 0)
parallel_divisor += leader_contribution;
}
return parallel_divisor;
}
/*
* compute_bitmap_pages
*
* compute number of pages fetched from heap in bitmap heap scan.
*/
double
compute_bitmap_pages(PlannerInfo *root, RelOptInfo *baserel, Path *bitmapqual,
int loop_count, Cost *cost, double *tuple)
{
Cost indexTotalCost;
Selectivity indexSelectivity;
double T;
double pages_fetched;
double tuples_fetched;
double heap_pages;
long maxentries;
/*
* Fetch total cost of obtaining the bitmap, as well as its total
* selectivity.
*/
cost_bitmap_tree_node(bitmapqual, &indexTotalCost, &indexSelectivity);
/*
* Estimate number of main-table pages fetched.
*/
tuples_fetched = clamp_row_est(indexSelectivity * baserel->tuples);
T = (baserel->pages > 1) ? (double) baserel->pages : 1.0;
/*
* For a single scan, the number of heap pages that need to be fetched is
* the same as the Mackert and Lohman formula for the case T <= b (ie, no
* re-reads needed).
*/
pages_fetched = (2.0 * T * tuples_fetched) / (2.0 * T + tuples_fetched);
/*
* Calculate the number of pages fetched from the heap. Then based on
* current work_mem estimate get the estimated maxentries in the bitmap.
* (Note that we always do this calculation based on the number of pages
* that would be fetched in a single iteration, even if loop_count > 1.
* That's correct, because only that number of entries will be stored in
* the bitmap at one time.)
*/
heap_pages = Min(pages_fetched, baserel->pages);
maxentries = tbm_calculate_entries(work_mem * 1024L);
if (loop_count > 1)
{
/*
* For repeated bitmap scans, scale up the number of tuples fetched in
* the Mackert and Lohman formula by the number of scans, so that we
* estimate the number of pages fetched by all the scans. Then
* pro-rate for one scan.
*/
pages_fetched = index_pages_fetched(tuples_fetched * loop_count,
baserel->pages,
get_indexpath_pages(bitmapqual),
root);
pages_fetched /= loop_count;
}
if (pages_fetched >= T)
pages_fetched = T;
else
pages_fetched = ceil(pages_fetched);
if (maxentries < heap_pages)
{
double exact_pages;
double lossy_pages;
/*
* Crude approximation of the number of lossy pages. Because of the
* way tbm_lossify() is coded, the number of lossy pages increases
* very sharply as soon as we run short of memory; this formula has
* that property and seems to perform adequately in testing, but it's
* possible we could do better somehow.
*/
lossy_pages = Max(0, heap_pages - maxentries / 2);
exact_pages = heap_pages - lossy_pages;
/*
* If there are lossy pages then recompute the number of tuples
* processed by the bitmap heap node. We assume here that the chance
* of a given tuple coming from an exact page is the same as the
* chance that a given page is exact. This might not be true, but
* it's not clear how we can do any better.
*/
if (lossy_pages > 0)
tuples_fetched =
clamp_row_est(indexSelectivity *
(exact_pages / heap_pages) * baserel->tuples +
(lossy_pages / heap_pages) * baserel->tuples);
}
if (cost)
*cost = indexTotalCost;
if (tuple)
*tuple = tuples_fetched;
return pages_fetched;
}
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