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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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11
src/backend/optimizer/plan/planner.c
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@ -341,12 +341,21 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
inline_set_returning_functions(root);
/*
* Check to see if any subqueries in the rangetable can be merged into
* Check to see if any subqueries in the jointree can be merged into
* this query.
*/
parse->jointree = (FromExpr *)
pull_up_subqueries(root, (Node *) parse->jointree, NULL, NULL);
/*
* If this is a simple UNION ALL query, flatten it into an appendrel.
* We do this now because it requires applying pull_up_subqueries to the
* leaf queries of the UNION ALL, which weren't touched above because they
* weren't referenced by the jointree (they will be after we do this).
*/
if (parse->setOperations)
flatten_simple_union_all(root);
/*
* Detect whether any rangetable entries are RTE_JOIN kind; if not, we can
* avoid the expense of doing flatten_join_alias_vars(). Also check for