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Wrap appendrel member outputs in PlaceHolderVars in additional cases.

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Add PlaceHolderVar wrappers as needed to make UNION ALL sub-select output
expressions appear non-constant and distinct from each other.  This makes
the world safe for add_child_rel_equivalences to do what it does.  Before,
it was possible for that function to add identical expressions to different
EquivalenceClasses, which logically should imply merging such ECs, which
would be wrong; or to improperly add a constant to an EquivalenceClass,
drastically changing its behavior.  Per report from Teodor Sigaev.

The only currently known consequence of this bug is "MergeAppend child's
targetlist doesn't match MergeAppend" planner failures in 9.1 and later.
I am suspicious that there may be other failure modes that could affect
older release branches; but in the absence of any hard evidence, I'll
refrain from back-patching further than 9.1.
This commit is contained in:
Tom Lane
2011-11-08 21:14:28 -05:00
parent b1c701c909
commit 7097e6c4a4
6 changed files with 138 additions and 20 deletions
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2
src/include/optimizer/placeholder.h
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@@ -21,7 +21,7 @@ extern PlaceHolderVar *make_placeholder_expr(PlannerInfo *root, Expr *expr,
Relids phrels);
extern PlaceHolderInfo *find_placeholder_info(PlannerInfo *root,
PlaceHolderVar *phv, bool create_new_ph);
extern void find_placeholders_in_jointree(PlannerInfo *root);
extern void find_placeholders_in_query(PlannerInfo *root);
extern void mark_placeholder_maybe_needed(PlannerInfo *root,
PlaceHolderInfo *phinfo, Relids relids);
extern void update_placeholder_eval_levels(PlannerInfo *root,