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Code review for Parallel Append.

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- Remove unnecessary #include mistakenly added in execnodes.h.
- Fix mistake in comment in choose_next_subplan_for_leader.
- Adjust row estimates in cost_append for a possibly-different
  parallel divisor.
- Clamp row estimates in cost_append after operations that may
  not produce integers.

Amit Kapila, with cosmetic adjustments by me.

Discussion: http://postgr.es/m/CAA4eK1+qcbeai3coPpRW=GFCzFeLUsuY4T-AKHqMjxpEGZBPQg@mail.gmail.com
This commit is contained in:
Robert Haas
2018-01-04 07:56:09 -05:00
parent 934c7986f4
commit c759395617
3 changed files with 15 additions and 9 deletions
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16
src/backend/optimizer/path/costsize.c
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@ -1883,18 +1883,26 @@ cost_append(AppendPath *apath)
subpath->startup_cost);
/*
* Apply parallel divisor to non-partial subpaths. Also add the
* cost of partial paths to the total cost, but ignore non-partial
* paths for now.
* 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
{
apath->path.rows += subpath->rows;
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++;
}