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Use appendrel planning logic for top-level UNION ALL structures.

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Formerly, we could convert a UNION ALL structure inside a subquery-in-FROM
into an appendrel, as a side effect of pulling up the subquery into its
parent; but top-level UNION ALL always caused use of plan_set_operations().
That didn't matter too much because you got an Append-based plan either
way.  However, now that the appendrel code can do things with MergeAppend,
it's worthwhile to hack up the top-level case so it also uses appendrels.

This is a bit of a stopgap; but going much further than this will require
a major rewrite of the planner's set-operations support, which I'm not
prepared to undertake now.  For the moment let's grab the low-hanging fruit.
This commit is contained in:
Tom Lane
2010-11-08 15:15:02 -05:00
parent 543d22fc74
commit 947d0c862c
3 changed files with 121 additions and 12 deletions
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src/include/optimizer/prep.h
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@@ -26,6 +26,7 @@ extern void inline_set_returning_functions(PlannerInfo *root);
extern Node *pull_up_subqueries(PlannerInfo *root, Node *jtnode,
JoinExpr *lowest_outer_join,
AppendRelInfo *containing_appendrel);
extern void flatten_simple_union_all(PlannerInfo *root);
extern void reduce_outer_joins(PlannerInfo *root);
extern Relids get_relids_in_jointree(Node *jtnode, bool include_joins);
extern Relids get_relids_for_join(PlannerInfo *root, int joinrelid);