Sort node for ORDER BY is suppressed if choosen index scan will
allways present tuples in the requested order. Jan
This commit is contained in:
Jan Wieck
parent
724119a979
commit
f3a6b38e32
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@ -7,7 +7,7 @@
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.39 1999/02/02 17:46:14 momjian Exp $
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* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.40 1999/02/03 19:31:24 wieck Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -50,6 +50,12 @@
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#include "executor/executor.h"
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#include "utils/builtins.h"
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#include "utils/syscache.h"
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#include "access/genam.h"
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#include "parser/parse_oper.h"
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static bool need_sortplan(List *sortcls, Plan *plan);
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static Plan *make_sortplan(List *tlist, List *sortcls, Plan *plannode);
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extern Plan *make_groupPlan(List **tlist, bool tuplePerGroup,
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List *groupClause, Plan *subplan);
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@ -344,7 +350,7 @@ union_planner(Query *parse)
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}
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else
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{
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if (parse->sortClause)
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if (parse->sortClause && need_sortplan(parse->sortClause, result_plan))
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return (make_sortplan(tlist, parse->sortClause, result_plan));
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else
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return ((Plan *) result_plan);
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@ -572,3 +578,170 @@ pg_checkretval(Oid rettype, QueryTreeList *queryTreeList)
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/* success */
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return;
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}
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/* ----------
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* Support function for need_sortplan
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* ----------
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*/
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static TargetEntry *
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get_matching_tle(Plan *plan, Resdom *resdom)
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{
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List *i;
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TargetEntry *tle;
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foreach (i, plan->targetlist) {
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tle = (TargetEntry *)lfirst(i);
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if (tle->resdom->resno == resdom->resno)
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return tle;
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}
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return NULL;
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}
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/* ----------
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* Check if a user requested ORDER BY is already satisfied by
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* the choosen index scan.
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*
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* Returns TRUE if sort is required, FALSE if can be omitted.
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* ----------
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*/
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static bool
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need_sortplan(List *sortcls, Plan *plan)
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{
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Relation indexRel;
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IndexScan *indexScan;
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Oid indexId;
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List *i;
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HeapTuple htup;
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Form_pg_index index_tup;
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int key_no = 0;
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/* ----------
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* Must be an IndexScan
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* ----------
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*/
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if (nodeTag(plan) != T_IndexScan) {
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return TRUE;
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}
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indexScan = (IndexScan *)plan;
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/* ----------
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* Should not have left- or righttree
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* ----------
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*/
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if (plan->lefttree != NULL) {
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return TRUE;
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}
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if (plan->righttree != NULL) {
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return TRUE;
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}
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/* ----------
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* Must be a single index scan
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* ----------
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*/
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if (length(indexScan->indxid) != 1) {
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return TRUE;
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}
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/* ----------
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* Indices can only have up to 8 attributes. So an ORDER BY using
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* more that 8 attributes could never be satisfied by an index.
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* ----------
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*/
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if (length(sortcls) > 8) {
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return TRUE;
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}
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/* ----------
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* The choosen Index must be a btree
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* ----------
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*/
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indexId = lfirsti(indexScan->indxid);
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indexRel = index_open(indexId);
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if (strcmp(nameout(&(indexRel->rd_am->amname)), "btree") != 0) {
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heap_close(indexRel);
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return TRUE;
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}
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heap_close(indexRel);
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/* ----------
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* Fetch the index tuple
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* ----------
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*/
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htup = SearchSysCacheTuple(INDEXRELID,
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ObjectIdGetDatum(indexId), 0, 0, 0);
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if (!HeapTupleIsValid(htup)) {
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elog(ERROR, "cache lookup for index %d failed", indexId);
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}
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index_tup = (Form_pg_index) GETSTRUCT(htup);
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/* ----------
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* Check if all the sort clauses match the attributes in the index
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* ----------
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*/
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foreach (i, sortcls) {
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SortClause *sortcl;
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Resdom *resdom;
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TargetEntry *tle;
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Var *var;
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sortcl = (SortClause *) lfirst(i);
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resdom = sortcl->resdom;
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tle = get_matching_tle(plan, resdom);
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if (tle == NULL) {
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/* ----------
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* Could this happen?
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* ----------
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*/
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return TRUE;
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}
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if (nodeTag(tle->expr) != T_Var) {
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/* ----------
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* The target list expression isn't a var, so it
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* cannot be the indexed attribute
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* ----------
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*/
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return TRUE;
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}
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var = (Var *)(tle->expr);
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if (var->varno != indexScan->scan.scanrelid) {
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/* ----------
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* This Var isn't from the scan relation. So it isn't
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* that of the index
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* ----------
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*/
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return TRUE;
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}
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if (var->varattno != index_tup->indkey[key_no]) {
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/* ----------
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* It isn't the indexed attribute.
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* ----------
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*/
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return TRUE;
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}
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if (oprid(oper("<", resdom->restype, resdom->restype, FALSE)) != sortcl->opoid) {
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/* ----------
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* Sort order isn't in ascending order.
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* ----------
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*/
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return TRUE;
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}
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key_no++;
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}
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/* ----------
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* Index matches ORDER BY - sort not required
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* ----------
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*/
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return FALSE;
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}
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