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Fix planner crash from pfree'ing a partial path that a GatherPath uses.

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We mustn't run generate_gather_paths() during add_paths_to_joinrel(),
because that function can be invoked multiple times for the same target
joinrel.  Not only is it wasteful to build GatherPaths repeatedly, but
a later add_partial_path() could delete the partial path that a previously
created GatherPath depends on.  Instead establish the convention that we
do generate_gather_paths() for a rel only just before set_cheapest().

The code was accidentally not broken for baserels, because as of today there
never is more than one partial path for a baserel.  But that assumption
obviously has a pretty short half-life, so move the generate_gather_paths()
calls for those cases as well.

Also add some generic comments explaining how and why this all works.

Per fuzz testing by Andreas Seltenreich.

Report: <871t5pgwdt.fsf@credativ.de>
This commit is contained in:
Tom Lane
2016-04-30 12:29:21 -04:00
parent 17d5db352c
commit c45bf5751b
5 changed files with 71 additions and 34 deletions
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7
src/backend/optimizer/path/joinpath.c
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@ -223,12 +223,7 @@ add_paths_to_joinrel(PlannerInfo *root,
jointype, &extra);
/*
* 6. Consider gathering partial paths.
*/
generate_gather_paths(root, joinrel);
/*
* 7. Finally, give extensions a chance to manipulate the path list.
* 6. Finally, give extensions a chance to manipulate the path list.
*/
if (set_join_pathlist_hook)
set_join_pathlist_hook(root, joinrel, outerrel, innerrel,