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Support parallel bitmap heap scans.

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The index is scanned by a single process, but then all cooperating
processes can iterate jointly over the resulting set of heap blocks.
In the future, we might also want to support using a parallel bitmap
index scan to set up for a parallel bitmap heap scan, but that's a
job for another day.

Dilip Kumar, with some corrections and cosmetic changes by me.  The
larger patch set of which this is a part has been reviewed and tested
by (at least) Andres Freund, Amit Khandekar, Tushar Ahuja, Rafia
Sabih, Haribabu Kommi, Thomas Munro, and me.

Discussion: http://postgr.es/m/CAFiTN-uc4=0WxRGfCzs-xfkMYcSEWUC-Fon6thkJGjkh9i=13A@mail.gmail.com
This commit is contained in:
Robert Haas
2017-03-08 12:05:43 -05:00
parent 4eafdcc276
commit f35742ccb7
24 changed files with 615 additions and 58 deletions
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16
src/backend/optimizer/path/costsize.c
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@@ -860,6 +860,7 @@ cost_bitmap_heap_scan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
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,
@@ -921,8 +922,21 @@ cost_bitmap_heap_scan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
startup_cost += qpqual_cost.startup;
cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple;
cpu_run_cost = cpu_per_tuple * tuples_fetched;
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;