allpaths.c

来自「PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统」· C语言 代码 · 共 1,160 行 · 第 1/3 页

	foreach(l, tlist)
	{
		TargetEntry *tle = (TargetEntry *) lfirst(l);

		if (tle->resjunk)
			continue;			/* ignore resjunk columns */
		if (colType == NULL)
			elog(ERROR, "wrong number of tlist entries");
		if (exprType((Node *) tle->expr) != lfirst_oid(colType))
			differentTypes[tle->resno] = true;
		colType = lnext(colType);
	}
	if (colType != NULL)
		elog(ERROR, "wrong number of tlist entries");
}

/*
 * qual_is_pushdown_safe - is a particular qual safe to push down?
 *
 * qual is a restriction clause applying to the given subquery (whose RTE
 * has index rti in the parent query).
 *
 * Conditions checked here:
 *
 * 1. The qual must not contain any subselects (mainly because I'm not sure
 * it will work correctly: sublinks will already have been transformed into
 * subplans in the qual, but not in the subquery).
 *
 * 2. The qual must not refer to the whole-row output of the subquery
 * (since there is no easy way to name that within the subquery itself).
 *
 * 3. The qual must not refer to any subquery output columns that were
 * found to have inconsistent types across a set operation tree by
 * subquery_is_pushdown_safe().
 *
 * 4. If the subquery uses DISTINCT ON, we must not push down any quals that
 * refer to non-DISTINCT output columns, because that could change the set
 * of rows returned.  This condition is vacuous for DISTINCT, because then
 * there are no non-DISTINCT output columns, but unfortunately it's fairly
 * expensive to tell the difference between DISTINCT and DISTINCT ON in the
 * parsetree representation.  It's cheaper to just make sure all the Vars
 * in the qual refer to DISTINCT columns.
 *
 * 5. We must not push down any quals that refer to subselect outputs that
 * return sets, else we'd introduce functions-returning-sets into the
 * subquery's WHERE/HAVING quals.
 */
static bool
qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
					  bool *differentTypes)
{
	bool		safe = true;
	List	   *vars;
	ListCell   *vl;
	Bitmapset  *tested = NULL;

	/* Refuse subselects (point 1) */
	if (contain_subplans(qual))
		return false;

	/*
	 * Examine all Vars used in clause; since it's a restriction clause, all
	 * such Vars must refer to subselect output columns.
	 */
	vars = pull_var_clause(qual, false);
	foreach(vl, vars)
	{
		Var		   *var = (Var *) lfirst(vl);
		TargetEntry *tle;

		Assert(var->varno == rti);

		/* Check point 2 */
		if (var->varattno == 0)
		{
			safe = false;
			break;
		}

		/*
		 * We use a bitmapset to avoid testing the same attno more than once.
		 * (NB: this only works because subquery outputs can't have negative
		 * attnos.)
		 */
		if (bms_is_member(var->varattno, tested))
			continue;
		tested = bms_add_member(tested, var->varattno);

		/* Check point 3 */
		if (differentTypes[var->varattno])
		{
			safe = false;
			break;
		}

		/* Must find the tlist element referenced by the Var */
		tle = get_tle_by_resno(subquery->targetList, var->varattno);
		Assert(tle != NULL);
		Assert(!tle->resjunk);

		/* If subquery uses DISTINCT or DISTINCT ON, check point 4 */
		if (subquery->distinctClause != NIL &&
			!targetIsInSortList(tle, subquery->distinctClause))
		{
			/* non-DISTINCT column, so fail */
			safe = false;
			break;
		}

		/* Refuse functions returning sets (point 5) */
		if (expression_returns_set((Node *) tle->expr))
		{
			safe = false;
			break;
		}
	}

	list_free(vars);
	bms_free(tested);

	return safe;
}

/*
 * subquery_push_qual - push down a qual that we have determined is safe
 */
static void
subquery_push_qual(Query *subquery, RangeTblEntry *rte, Index rti, Node *qual)
{
	if (subquery->setOperations != NULL)
	{
		/* Recurse to push it separately to each component query */
		recurse_push_qual(subquery->setOperations, subquery,
						  rte, rti, qual);
	}
	else
	{
		/*
		 * We need to replace Vars in the qual (which must refer to outputs of
		 * the subquery) with copies of the subquery's targetlist expressions.
		 * Note that at this point, any uplevel Vars in the qual should have
		 * been replaced with Params, so they need no work.
		 *
		 * This step also ensures that when we are pushing into a setop tree,
		 * each component query gets its own copy of the qual.
		 */
		qual = ResolveNew(qual, rti, 0, rte,
						  subquery->targetList,
						  CMD_SELECT, 0);

		/*
		 * Now attach the qual to the proper place: normally WHERE, but if the
		 * subquery uses grouping or aggregation, put it in HAVING (since the
		 * qual really refers to the group-result rows).
		 */
		if (subquery->hasAggs || subquery->groupClause || subquery->havingQual)
			subquery->havingQual = make_and_qual(subquery->havingQual, qual);
		else
			subquery->jointree->quals =
				make_and_qual(subquery->jointree->quals, qual);

		/*
		 * We need not change the subquery's hasAggs or hasSublinks flags,
		 * since we can't be pushing down any aggregates that weren't there
		 * before, and we don't push down subselects at all.
		 */
	}
}

/*
 * Helper routine to recurse through setOperations tree
 */
static void
recurse_push_qual(Node *setOp, Query *topquery,
				  RangeTblEntry *rte, Index rti, Node *qual)
{
	if (IsA(setOp, RangeTblRef))
	{
		RangeTblRef *rtr = (RangeTblRef *) setOp;
		RangeTblEntry *subrte = rt_fetch(rtr->rtindex, topquery->rtable);
		Query	   *subquery = subrte->subquery;

		Assert(subquery != NULL);
		subquery_push_qual(subquery, rte, rti, qual);
	}
	else if (IsA(setOp, SetOperationStmt))
	{
		SetOperationStmt *op = (SetOperationStmt *) setOp;

		recurse_push_qual(op->larg, topquery, rte, rti, qual);
		recurse_push_qual(op->rarg, topquery, rte, rti, qual);
	}
	else
	{
		elog(ERROR, "unrecognized node type: %d",
			 (int) nodeTag(setOp));
	}
}

/*****************************************************************************
 *			DEBUG SUPPORT
 *****************************************************************************/

#ifdef OPTIMIZER_DEBUG

static void
print_relids(Relids relids)
{
	Relids		tmprelids;
	int			x;
	bool		first = true;

	tmprelids = bms_copy(relids);
	while ((x = bms_first_member(tmprelids)) >= 0)
	{
		if (!first)
			printf(" ");
		printf("%d", x);
		first = false;
	}
	bms_free(tmprelids);
}

static void
print_restrictclauses(PlannerInfo *root, List *clauses)
{
	ListCell   *l;

	foreach(l, clauses)
	{
		RestrictInfo *c = lfirst(l);

		print_expr((Node *) c->clause, root->parse->rtable);
		if (lnext(l))
			printf(", ");
	}
}

static void
print_path(PlannerInfo *root, Path *path, int indent)
{
	const char *ptype;
	bool		join = false;
	Path	   *subpath = NULL;
	int			i;

	switch (nodeTag(path))
	{
		case T_Path:
			ptype = "SeqScan";
			break;
		case T_IndexPath:
			ptype = "IdxScan";
			break;
		case T_BitmapHeapPath:
			ptype = "BitmapHeapScan";
			break;
		case T_BitmapAndPath:
			ptype = "BitmapAndPath";
			break;
		case T_BitmapOrPath:
			ptype = "BitmapOrPath";
			break;
		case T_TidPath:
			ptype = "TidScan";
			break;
		case T_AppendPath:
			ptype = "Append";
			break;
		case T_ResultPath:
			ptype = "Result";
			subpath = ((ResultPath *) path)->subpath;
			break;
		case T_MaterialPath:
			ptype = "Material";
			subpath = ((MaterialPath *) path)->subpath;
			break;
		case T_UniquePath:
			ptype = "Unique";
			subpath = ((UniquePath *) path)->subpath;
			break;
		case T_NestPath:
			ptype = "NestLoop";
			join = true;
			break;
		case T_MergePath:
			ptype = "MergeJoin";
			join = true;
			break;
		case T_HashPath:
			ptype = "HashJoin";
			join = true;
			break;
		default:
			ptype = "???Path";
			break;
	}

	for (i = 0; i < indent; i++)
		printf("\t");
	printf("%s", ptype);

	if (path->parent)
	{
		printf("(");
		print_relids(path->parent->relids);
		printf(") rows=%.0f", path->parent->rows);
	}
	printf(" cost=%.2f..%.2f\n", path->startup_cost, path->total_cost);

	if (path->pathkeys)
	{
		for (i = 0; i < indent; i++)
			printf("\t");
		printf("  pathkeys: ");
		print_pathkeys(path->pathkeys, root->parse->rtable);
	}

	if (join)
	{
		JoinPath   *jp = (JoinPath *) path;

		for (i = 0; i < indent; i++)
			printf("\t");
		printf("  clauses: ");
		print_restrictclauses(root, jp->joinrestrictinfo);
		printf("\n");

		if (IsA(path, MergePath))
		{
			MergePath  *mp = (MergePath *) path;

			if (mp->outersortkeys || mp->innersortkeys)
			{
				for (i = 0; i < indent; i++)
					printf("\t");
				printf("  sortouter=%d sortinner=%d\n",
					   ((mp->outersortkeys) ? 1 : 0),
					   ((mp->innersortkeys) ? 1 : 0));
			}
		}

		print_path(root, jp->outerjoinpath, indent + 1);
		print_path(root, jp->innerjoinpath, indent + 1);
	}

	if (subpath)
		print_path(root, subpath, indent + 1);
}

void
debug_print_rel(PlannerInfo *root, RelOptInfo *rel)
{
	ListCell   *l;

	printf("RELOPTINFO (");
	print_relids(rel->relids);
	printf("): rows=%.0f width=%d\n", rel->rows, rel->width);

	if (rel->baserestrictinfo)
	{
		printf("\tbaserestrictinfo: ");
		print_restrictclauses(root, rel->baserestrictinfo);
		printf("\n");
	}

	if (rel->joininfo)
	{
		printf("\tjoininfo: ");
		print_restrictclauses(root, rel->joininfo);
		printf("\n");
	}

	printf("\tpath list:\n");
	foreach(l, rel->pathlist)
		print_path(root, lfirst(l), 1);
	printf("\n\tcheapest startup path:\n");
	print_path(root, rel->cheapest_startup_path, 1);
	printf("\n\tcheapest total path:\n");
	print_path(root, rel->cheapest_total_path, 1);
	printf("\n");
	fflush(stdout);
}

#endif   /* OPTIMIZER_DEBUG */