planagg.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

 * Note: check_partial_indexes() must have been run previously.
 */
static bool
build_minmax_path(PlannerInfo *root, RelOptInfo *rel, MinMaxAggInfo *info)
{
	IndexPath  *best_path = NULL;
	Cost		best_cost = 0;
	ListCell   *l;

	foreach(l, rel->indexlist)
	{
		IndexOptInfo *index = (IndexOptInfo *) lfirst(l);
		ScanDirection indexscandir = NoMovementScanDirection;
		int			indexcol;
		int			prevcol;
		List	   *restrictclauses;
		IndexPath  *new_path;
		Cost		new_cost;
		bool		found_clause;

		/* Ignore non-btree indexes */
		if (index->relam != BTREE_AM_OID)
			continue;

		/* Ignore partial indexes that do not match the query */
		if (index->indpred != NIL && !index->predOK)
			continue;

		/*
		 * Look for a match to one of the index columns.  (In a stupidly
		 * designed index, there could be multiple matches, but we only care
		 * about the first one.)
		 */
		for (indexcol = 0; indexcol < index->ncolumns; indexcol++)
		{
			indexscandir = match_agg_to_index_col(info, index, indexcol);
			if (!ScanDirectionIsNoMovement(indexscandir))
				break;
		}
		if (ScanDirectionIsNoMovement(indexscandir))
			continue;

		/*
		 * If the match is not at the first index column, we have to verify
		 * that there are "x = something" restrictions on all the earlier
		 * index columns.  Since we'll need the restrictclauses list anyway to
		 * build the path, it's convenient to extract that first and then look
		 * through it for the equality restrictions.
		 */
		restrictclauses = group_clauses_by_indexkey(index,
												index->rel->baserestrictinfo,
													NIL,
													NULL,
													&found_clause);

		if (list_length(restrictclauses) < indexcol)
			continue;			/* definitely haven't got enough */
		for (prevcol = 0; prevcol < indexcol; prevcol++)
		{
			List	   *rinfos = (List *) list_nth(restrictclauses, prevcol);
			ListCell   *ll;

			foreach(ll, rinfos)
			{
				RestrictInfo *rinfo = (RestrictInfo *) lfirst(ll);
				int			strategy;

				Assert(is_opclause(rinfo->clause));
				strategy =
					get_op_opclass_strategy(((OpExpr *) rinfo->clause)->opno,
											index->classlist[prevcol]);
				if (strategy == BTEqualStrategyNumber)
					break;
			}
			if (ll == NULL)
				break;			/* none are Equal for this index col */
		}
		if (prevcol < indexcol)
			continue;			/* didn't find all Equal clauses */

		/*
		 * Build the access path.  We don't bother marking it with pathkeys.
		 */
		new_path = create_index_path(root, index,
									 restrictclauses,
									 NIL,
									 indexscandir,
									 false);

		/*
		 * Estimate actual cost of fetching just one row.
		 */
		if (new_path->rows > 1.0)
			new_cost = new_path->path.startup_cost +
				(new_path->path.total_cost - new_path->path.startup_cost)
				* 1.0 / new_path->rows;
		else
			new_cost = new_path->path.total_cost;

		/*
		 * Keep if first or if cheaper than previous best.
		 */
		if (best_path == NULL || new_cost < best_cost)
		{
			best_path = new_path;
			best_cost = new_cost;
		}
	}

	info->path = best_path;
	info->pathcost = best_cost;
	return (best_path != NULL);
}

/*
 * match_agg_to_index_col
 *		Does an aggregate match an index column?
 *
 * It matches if its argument is equal to the index column's data and its
 * sortop is either the LessThan or GreaterThan member of the column's opclass.
 *
 * We return ForwardScanDirection if match the LessThan member,
 * BackwardScanDirection if match the GreaterThan member,
 * and NoMovementScanDirection if there's no match.
 */
static ScanDirection
match_agg_to_index_col(MinMaxAggInfo *info, IndexOptInfo *index, int indexcol)
{
	int			strategy;

	/* Check for data match */
	if (!match_index_to_operand((Node *) info->target, indexcol, index))
		return NoMovementScanDirection;

	/* Look up the operator in the opclass */
	strategy = get_op_opclass_strategy(info->aggsortop,
									   index->classlist[indexcol]);
	if (strategy == BTLessStrategyNumber)
		return ForwardScanDirection;
	if (strategy == BTGreaterStrategyNumber)
		return BackwardScanDirection;
	return NoMovementScanDirection;
}

/*
 * Construct a suitable plan for a converted aggregate query
 */
static void
make_agg_subplan(PlannerInfo *root, MinMaxAggInfo *info, List *constant_quals)
{
	PlannerInfo subroot;
	Query	   *subparse;
	Plan	   *plan;
	TargetEntry *tle;
	SortClause *sortcl;
	NullTest   *ntest;

	/*
	 * Generate a suitably modified query.	Much of the work here is probably
	 * unnecessary in the normal case, but we want to make it look good if
	 * someone tries to EXPLAIN the result.
	 */
	memcpy(&subroot, root, sizeof(PlannerInfo));
	subroot.parse = subparse = (Query *) copyObject(root->parse);
	subparse->commandType = CMD_SELECT;
	subparse->resultRelation = 0;
	subparse->resultRelations = NIL;
	subparse->into = NULL;
	subparse->hasAggs = false;
	subparse->groupClause = NIL;
	subparse->havingQual = NULL;
	subparse->distinctClause = NIL;
	subroot.hasHavingQual = false;

	/* single tlist entry that is the aggregate target */
	tle = makeTargetEntry(copyObject(info->target),
						  1,
						  pstrdup("agg_target"),
						  false);
	subparse->targetList = list_make1(tle);

	/* set up the appropriate ORDER BY entry */
	sortcl = makeNode(SortClause);
	sortcl->tleSortGroupRef = assignSortGroupRef(tle, subparse->targetList);
	sortcl->sortop = info->aggsortop;
	subparse->sortClause = list_make1(sortcl);

	/* set up LIMIT 1 */
	subparse->limitOffset = NULL;
	subparse->limitCount = (Node *) makeConst(INT4OID, sizeof(int4),
											  Int32GetDatum(1),
											  false, true);

	/*
	 * Generate the plan for the subquery.	We already have a Path for the
	 * basic indexscan, but we have to convert it to a Plan and attach a LIMIT
	 * node above it.  We might need a gating Result, too, to handle any
	 * non-variable qual clauses.
	 *
	 * Also we must add a "WHERE foo IS NOT NULL" restriction to the
	 * indexscan, to be sure we don't return a NULL, which'd be contrary to
	 * the standard behavior of MIN/MAX.  XXX ideally this should be done
	 * earlier, so that the selectivity of the restriction could be included
	 * in our cost estimates.  But that looks painful, and in most cases the
	 * fraction of NULLs isn't high enough to change the decision.
	 */
	plan = create_plan(&subroot, (Path *) info->path);

	plan->targetlist = copyObject(subparse->targetList);

	ntest = makeNode(NullTest);
	ntest->nulltesttype = IS_NOT_NULL;
	ntest->arg = copyObject(info->target);

	plan->qual = lcons(ntest, plan->qual);

	if (constant_quals)
		plan = (Plan *) make_result(copyObject(plan->targetlist),
									copyObject(constant_quals),
									plan);

	plan = (Plan *) make_limit(plan,
							   subparse->limitOffset,
							   subparse->limitCount,
							   0, 1);

	/*
	 * Convert the plan into an InitPlan, and make a Param for its result.
	 */
	info->param = SS_make_initplan_from_plan(&subroot, plan,
											 exprType((Node *) tle->expr),
											 -1);
}

/*
 * Replace original aggregate calls with subplan output Params
 */
static Node *
replace_aggs_with_params_mutator(Node *node, List **context)
{
	if (node == NULL)
		return NULL;
	if (IsA(node, Aggref))
	{
		Aggref	   *aggref = (Aggref *) node;
		ListCell   *l;

		foreach(l, *context)
		{
			MinMaxAggInfo *info = (MinMaxAggInfo *) lfirst(l);

			if (info->aggfnoid == aggref->aggfnoid &&
				equal(info->target, aggref->target))
				return (Node *) info->param;
		}
		elog(ERROR, "failed to re-find aggregate info record");
	}
	Assert(!IsA(node, SubLink));
	return expression_tree_mutator(node, replace_aggs_with_params_mutator,
								   (void *) context);
}

/*
 * Get the OID of the sort operator, if any, associated with an aggregate.
 * Returns InvalidOid if there is no such operator.
 */
static Oid
fetch_agg_sort_op(Oid aggfnoid)
{
	HeapTuple	aggTuple;
	Form_pg_aggregate aggform;
	Oid			aggsortop;

	/* fetch aggregate entry from pg_aggregate */
	aggTuple = SearchSysCache(AGGFNOID,
							  ObjectIdGetDatum(aggfnoid),
							  0, 0, 0);
	if (!HeapTupleIsValid(aggTuple))
		return InvalidOid;
	aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple);
	aggsortop = aggform->aggsortop;
	ReleaseSysCache(aggTuple);

	return aggsortop;
}