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Extend CTE patch to support recursive UNION (ie, without ALL). The

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implementation uses an in-memory hash table, so it will poop out for very
large recursive results ... but the performance characteristics of a
sort-based implementation would be pretty unpleasant too.
This commit is contained in:
Tom Lane
2008-10-07 19:27:04 +00:00
parent 059349be0c
commit 0d115dde82
13 changed files with 345 additions and 74 deletions
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45
src/backend/optimizer/prep/prepunion.c
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@ -22,7 +22,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/prep/prepunion.c,v 1.157 2008/10/06 17:39:26 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/prep/prepunion.c,v 1.158 2008/10/07 19:27:04 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -318,10 +318,12 @@ generate_recursion_plan(SetOperationStmt *setOp, PlannerInfo *root,
Plan *lplan;
Plan *rplan;
List *tlist;
List *groupList;
long numGroups;
/* Parser should have rejected other cases */
if (setOp->op != SETOP_UNION || !setOp->all)
elog(ERROR, "only UNION ALL queries can be recursive");
if (setOp->op != SETOP_UNION)
elog(ERROR, "only UNION queries can be recursive");
/* Worktable ID should be assigned */
Assert(root->wt_param_id >= 0);
@ -346,13 +348,46 @@ generate_recursion_plan(SetOperationStmt *setOp, PlannerInfo *root,
list_make2(lplan, rplan),
refnames_tlist);
/*
* If UNION, identify the grouping operators
*/
if (setOp->all)
{
groupList = NIL;
numGroups = 0;
}
else
{
double dNumGroups;
/* Identify the grouping semantics */
groupList = generate_setop_grouplist(setOp, tlist);
/* We only support hashing here */
if (!grouping_is_hashable(groupList))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("could not implement recursive UNION"),
errdetail("All column datatypes must be hashable.")));
/*
* For the moment, take the number of distinct groups as equal to
* the total input size, ie, the worst case.
*/
dNumGroups = lplan->plan_rows + rplan->plan_rows * 10;
/* Also convert to long int --- but 'ware overflow! */
numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
}
/*
* And make the plan node.
*/
plan = (Plan *) make_recursive_union(tlist, lplan, rplan,
root->wt_param_id);
root->wt_param_id,
groupList, numGroups);
*sortClauses = NIL; /* result of UNION ALL is always unsorted */
*sortClauses = NIL; /* RecursiveUnion result is always unsorted */
return plan;
}