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Commitda08a65

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Refactor bitmap heap scan estimation of heap pages fetched.
Currently, we only need this logic in order to cost a Bitmap HeapScan. But a pending patch for Parallel Bitmap Heap Scan also usesit to help figure out how many workers to use for the scan, whichhas to be determined prior to costing. So, move the logic toa separate function to make that easier.Dilip Kumar. The patch series of which this is a part has beenreviewed by Andres Freund, Amit Khendekar, Tushar Ahuja, RafiaSabih, Haribabu Kommi, and me; it is not clear from the emaildiscussion which of those people have looked specifically at thispart.Discussion:http://postgr.es/m/CAFiTN-v3QYNJEZnnmKCeATuLbN-h9tMVfeEF0+BrouYDqjXgwg@mail.gmail.com
1 parent350cb92 commitda08a65

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2 files changed

+72
-41
lines changed

2 files changed

+72
-41
lines changed

‎src/backend/optimizer/path/costsize.c

Lines changed: 70 additions & 41 deletions
Original file line numberDiff line numberDiff line change
@@ -813,7 +813,6 @@ cost_bitmap_heap_scan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
813813
Coststartup_cost=0;
814814
Costrun_cost=0;
815815
CostindexTotalCost;
816-
SelectivityindexSelectivity;
817816
QualCostqpqual_cost;
818817
Costcpu_per_tuple;
819818
Costcost_per_page;
@@ -837,54 +836,18 @@ cost_bitmap_heap_scan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
837836
if (!enable_bitmapscan)
838837
startup_cost+=disable_cost;
839838

840-
/*
841-
* Fetch total cost of obtaining the bitmap, as well as its total
842-
* selectivity.
843-
*/
844-
cost_bitmap_tree_node(bitmapqual,&indexTotalCost,&indexSelectivity);
839+
pages_fetched=compute_bitmap_pages(root,baserel,bitmapqual,
840+
loop_count,&indexTotalCost,
841+
&tuples_fetched);
845842

846843
startup_cost+=indexTotalCost;
844+
T= (baserel->pages>1) ? (double)baserel->pages :1.0;
847845

848846
/* Fetch estimated page costs for tablespace containing table. */
849847
get_tablespace_page_costs(baserel->reltablespace,
850848
&spc_random_page_cost,
851849
&spc_seq_page_cost);
852850

853-
/*
854-
* Estimate number of main-table pages fetched.
855-
*/
856-
tuples_fetched=clamp_row_est(indexSelectivity*baserel->tuples);
857-
858-
T= (baserel->pages>1) ? (double)baserel->pages :1.0;
859-
860-
if (loop_count>1)
861-
{
862-
/*
863-
* For repeated bitmap scans, scale up the number of tuples fetched in
864-
* the Mackert and Lohman formula by the number of scans, so that we
865-
* estimate the number of pages fetched by all the scans. Then
866-
* pro-rate for one scan.
867-
*/
868-
pages_fetched=index_pages_fetched(tuples_fetched*loop_count,
869-
baserel->pages,
870-
get_indexpath_pages(bitmapqual),
871-
root);
872-
pages_fetched /=loop_count;
873-
}
874-
else
875-
{
876-
/*
877-
* For a single scan, the number of heap pages that need to be fetched
878-
* is the same as the Mackert and Lohman formula for the case T <= b
879-
* (ie, no re-reads needed).
880-
*/
881-
pages_fetched= (2.0*T*tuples_fetched) / (2.0*T+tuples_fetched);
882-
}
883-
if (pages_fetched >=T)
884-
pages_fetched=T;
885-
else
886-
pages_fetched=ceil(pages_fetched);
887-
888851
/*
889852
* For small numbers of pages we should charge spc_random_page_cost
890853
* apiece, while if nearly all the table's pages are being read, it's more
@@ -4820,3 +4783,69 @@ get_parallel_divisor(Path *path)
48204783

48214784
returnparallel_divisor;
48224785
}
4786+
4787+
/*
4788+
* compute_bitmap_pages
4789+
*
4790+
* compute number of pages fetched from heap in bitmap heap scan.
4791+
*/
4792+
double
4793+
compute_bitmap_pages(PlannerInfo*root,RelOptInfo*baserel,Path*bitmapqual,
4794+
intloop_count,Cost*cost,double*tuple)
4795+
{
4796+
CostindexTotalCost;
4797+
SelectivityindexSelectivity;
4798+
doubleT;
4799+
doublepages_fetched;
4800+
doubletuples_fetched;
4801+
4802+
/*
4803+
* Fetch total cost of obtaining the bitmap, as well as its total
4804+
* selectivity.
4805+
*/
4806+
cost_bitmap_tree_node(bitmapqual,&indexTotalCost,&indexSelectivity);
4807+
4808+
/*
4809+
* Estimate number of main-table pages fetched.
4810+
*/
4811+
tuples_fetched=clamp_row_est(indexSelectivity*baserel->tuples);
4812+
4813+
T= (baserel->pages>1) ? (double)baserel->pages :1.0;
4814+
4815+
if (loop_count>1)
4816+
{
4817+
/*
4818+
* For repeated bitmap scans, scale up the number of tuples fetched in
4819+
* the Mackert and Lohman formula by the number of scans, so that we
4820+
* estimate the number of pages fetched by all the scans. Then
4821+
* pro-rate for one scan.
4822+
*/
4823+
pages_fetched=index_pages_fetched(tuples_fetched*loop_count,
4824+
baserel->pages,
4825+
get_indexpath_pages(bitmapqual),
4826+
root);
4827+
pages_fetched /=loop_count;
4828+
}
4829+
else
4830+
{
4831+
/*
4832+
* For a single scan, the number of heap pages that need to be fetched
4833+
* is the same as the Mackert and Lohman formula for the case T <= b
4834+
* (ie, no re-reads needed).
4835+
*/
4836+
pages_fetched=
4837+
(2.0*T*tuples_fetched) / (2.0*T+tuples_fetched);
4838+
}
4839+
4840+
if (pages_fetched >=T)
4841+
pages_fetched=T;
4842+
else
4843+
pages_fetched=ceil(pages_fetched);
4844+
4845+
if (cost)
4846+
*cost=indexTotalCost;
4847+
if (tuple)
4848+
*tuple=tuples_fetched;
4849+
4850+
returnpages_fetched;
4851+
}

‎src/include/optimizer/cost.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -183,6 +183,8 @@ extern void set_cte_size_estimates(PlannerInfo *root, RelOptInfo *rel,
183183
doublecte_rows);
184184
externvoidset_foreign_size_estimates(PlannerInfo*root,RelOptInfo*rel);
185185
externPathTarget*set_pathtarget_cost_width(PlannerInfo*root,PathTarget*target);
186+
externdoublecompute_bitmap_pages(PlannerInfo*root,RelOptInfo*baserel,
187+
Path*bitmapqual,intloop_count,Cost*cost,double*tuple);
186188

187189
/*
188190
* prototypes for clausesel.c

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