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Preparatory refactoring for parallel merge join support.

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Extract the logic used by hash_inner_and_outer into a separate
function, get_cheapest_parallel_safe_total_inner, so that it can
also be used to plan parallel merge joins.

Also, add a require_parallel_safe argument to the existing function
get_cheapest_path_for_pathkeys, because parallel merge join needs
to find the cheapest path for a given set of pathkeys that is
parallel-safe, not just the cheapest one overall.

Patch by me, reviewed by Dilip Kumar.

Discussion: http://postgr.es/m/CA+TgmoYOv+dFK0MWW6366dFj_xTnohQfoBDrHyB7d1oZhrgPjA@mail.gmail.com
This commit is contained in:
Robert Haas
2017-03-07 10:33:29 -05:00
parent 655393a022
commit a71f10189d
4 changed files with 43 additions and 22 deletions
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29
src/backend/optimizer/path/pathkeys.c
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@@ -337,11 +337,13 @@ pathkeys_contained_in(List *keys1, List *keys2)
* 'pathkeys' represents a required ordering (in canonical form!)
* 'required_outer' denotes allowable outer relations for parameterized paths
* 'cost_criterion' is STARTUP_COST or TOTAL_COST
* 'require_parallel_safe' causes us to consider only parallel-safe paths
*/
Path *
get_cheapest_path_for_pathkeys(List *paths, List *pathkeys,
Relids required_outer,
CostSelector cost_criterion)
CostSelector cost_criterion,
bool require_parallel_safe)
{
Path *matched_path = NULL;
ListCell *l;
@@ -358,6 +360,9 @@ get_cheapest_path_for_pathkeys(List *paths, List *pathkeys,
compare_path_costs(matched_path, path, cost_criterion) <= 0)
continue;
if (require_parallel_safe && !path->parallel_safe)
continue;
if (pathkeys_contained_in(pathkeys, path->pathkeys) &&
bms_is_subset(PATH_REQ_OUTER(path), required_outer))
matched_path = path;
@@ -407,6 +412,28 @@ get_cheapest_fractional_path_for_pathkeys(List *paths,
return matched_path;
}
/*
* get_cheapest_parallel_safe_total_inner
* Find the unparameterized parallel-safe path with the least total cost.
*/
Path *
get_cheapest_parallel_safe_total_inner(List *paths)
{
ListCell *l;
foreach(l, paths)
{
Path *innerpath = (Path *) lfirst(l);
if (innerpath->parallel_safe &&
bms_is_empty(PATH_REQ_OUTER(innerpath)))
return innerpath;
}
return NULL;
}
/****************************************************************************
* NEW PATHKEY FORMATION
****************************************************************************/