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Teach tuplesort.c about "top N" sorting, in which only the first N tuples

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need be returned.  We keep a heap of the current best N tuples and sift-up
new tuples into it as we scan the input.  For M input tuples this means
only about M*log(N) comparisons instead of M*log(M), not to mention a lot
less workspace when N is small --- avoiding spill-to-disk for large M
is actually the most attractive thing about it.  Patch includes planner
and executor support for invoking this facility in ORDER BY ... LIMIT
queries.  Greg Stark, with some editorialization by moi.
This commit is contained in:
Tom Lane
2007-05-04 01:13:45 +00:00
parent 0fef38da21
commit d26559dbf3
13 changed files with 465 additions and 59 deletions
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31
src/backend/optimizer/plan/createplan.c
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@ -10,7 +10,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.229 2007/04/21 21:01:44 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.230 2007/05/04 01:13:44 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -122,7 +122,8 @@ static MergeJoin *make_mergejoin(List *tlist,
Plan *lefttree, Plan *righttree,
JoinType jointype);
static Sort *make_sort(PlannerInfo *root, Plan *lefttree, int numCols,
AttrNumber *sortColIdx, Oid *sortOperators, bool *nullsFirst);
AttrNumber *sortColIdx, Oid *sortOperators, bool *nullsFirst,
double limit_tuples);
/*
@ -1579,7 +1580,8 @@ create_mergejoin_plan(PlannerInfo *root,
outer_plan = (Plan *)
make_sort_from_pathkeys(root,
outer_plan,
best_path->outersortkeys);
best_path->outersortkeys,
-1.0);
outerpathkeys = best_path->outersortkeys;
}
else
@ -1591,7 +1593,8 @@ create_mergejoin_plan(PlannerInfo *root,
inner_plan = (Plan *)
make_sort_from_pathkeys(root,
inner_plan,
best_path->innersortkeys);
best_path->innersortkeys,
-1.0);
innerpathkeys = best_path->innersortkeys;
}
else
@ -2589,11 +2592,13 @@ make_mergejoin(List *tlist,
* make_sort --- basic routine to build a Sort plan node
*
* Caller must have built the sortColIdx, sortOperators, and nullsFirst
* arrays already.
* arrays already. limit_tuples is as for cost_sort (in particular, pass
* -1 if no limit)
*/
static Sort *
make_sort(PlannerInfo *root, Plan *lefttree, int numCols,
AttrNumber *sortColIdx, Oid *sortOperators, bool *nullsFirst)
AttrNumber *sortColIdx, Oid *sortOperators, bool *nullsFirst,
double limit_tuples)
{
Sort *node = makeNode(Sort);
Plan *plan = &node->plan;
@ -2603,7 +2608,8 @@ make_sort(PlannerInfo *root, Plan *lefttree, int numCols,
cost_sort(&sort_path, root, NIL,
lefttree->total_cost,
lefttree->plan_rows,
lefttree->plan_width);
lefttree->plan_width,
limit_tuples);
plan->startup_cost = sort_path.startup_cost;
plan->total_cost = sort_path.total_cost;
plan->targetlist = lefttree->targetlist;
@ -2664,6 +2670,8 @@ add_sort_column(AttrNumber colIdx, Oid sortOp, bool nulls_first,
*
* 'lefttree' is the node which yields input tuples
* 'pathkeys' is the list of pathkeys by which the result is to be sorted
* 'limit_tuples' is the bound on the number of output tuples;
* -1 if no bound
*
* We must convert the pathkey information into arrays of sort key column
* numbers and sort operator OIDs.
@ -2675,7 +2683,8 @@ add_sort_column(AttrNumber colIdx, Oid sortOp, bool nulls_first,
* adding a Result node just to do the projection.
*/
Sort *
make_sort_from_pathkeys(PlannerInfo *root, Plan *lefttree, List *pathkeys)
make_sort_from_pathkeys(PlannerInfo *root, Plan *lefttree, List *pathkeys,
double limit_tuples)
{
List *tlist = lefttree->targetlist;
ListCell *i;
@ -2810,7 +2819,7 @@ make_sort_from_pathkeys(PlannerInfo *root, Plan *lefttree, List *pathkeys)
Assert(numsortkeys > 0);
return make_sort(root, lefttree, numsortkeys,
sortColIdx, sortOperators, nullsFirst);
sortColIdx, sortOperators, nullsFirst, limit_tuples);
}
/*
@ -2859,7 +2868,7 @@ make_sort_from_sortclauses(PlannerInfo *root, List *sortcls, Plan *lefttree)
Assert(numsortkeys > 0);
return make_sort(root, lefttree, numsortkeys,
sortColIdx, sortOperators, nullsFirst);
sortColIdx, sortOperators, nullsFirst, -1.0);
}
/*
@ -2919,7 +2928,7 @@ make_sort_from_groupcols(PlannerInfo *root,
Assert(numsortkeys > 0);
return make_sort(root, lefttree, numsortkeys,
sortColIdx, sortOperators, nullsFirst);
sortColIdx, sortOperators, nullsFirst, -1.0);
}
Material *