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Add an at-least-marginally-plausible method of estimating the number

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of groups produced by GROUP BY.  This improves the accuracy of planning
estimates for grouped subselects, and is needed to check whether a
hashed aggregation plan risks memory overflow.
This commit is contained in:
Tom Lane
2002-11-19 23:22:00 +00:00
parent 54cb1db6cf
commit b60be3f2f8
11 changed files with 454 additions and 75 deletions
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20
src/backend/optimizer/plan/setrefs.c
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@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/setrefs.c,v 1.81 2002/09/04 20:31:21 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/setrefs.c,v 1.82 2002/11/19 23:21:59 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -439,7 +439,14 @@ join_references_mutator(Node *node,
return (Node *) newvar;
}
/* Perhaps it's a join alias that can be resolved to input vars? */
/* Return the Var unmodified, if it's for acceptable_rel */
if (var->varno == context->acceptable_rel)
return (Node *) copyObject(var);
/*
* Perhaps it's a join alias that can be resolved to input vars?
* We try this last since it's relatively slow.
*/
newnode = flatten_join_alias_vars((Node *) var,
context->rtable,
true);
@ -450,13 +457,8 @@ join_references_mutator(Node *node,
return newnode;
}
/*
* No referent found for Var --- either raise an error, or return
* the Var unmodified if it's for acceptable_rel.
*/
if (var->varno != context->acceptable_rel)
elog(ERROR, "join_references: variable not in subplan target lists");
return (Node *) copyObject(var);
/* No referent found for Var */
elog(ERROR, "join_references: variable not in subplan target lists");
}
return expression_tree_mutator(node,
join_references_mutator,