prepjointree.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

				reduce_outer_joins_pass2(j->rarg, right_state, root,
										 pass_nonnullable);
			}
			bms_free(local_nonnullable);
		}
	}
	else
		elog(ERROR, "unrecognized node type: %d",
			 (int) nodeTag(jtnode));
}

/*
 * find_nonnullable_rels
 *		Determine which base rels are forced nonnullable by given quals
 *
 * We don't use expression_tree_walker here because we don't want to
 * descend through very many kinds of nodes; only the ones we can be sure
 * are strict.	We can descend through the top level of implicit AND'ing,
 * but not through any explicit ANDs (or ORs) below that, since those are not
 * strict constructs.  The List case handles the top-level implicit AND list
 * as well as lists of arguments to strict operators/functions.
 */
static Relids
find_nonnullable_rels(Node *node, bool top_level)
{
	Relids		result = NULL;

	if (node == NULL)
		return NULL;
	if (IsA(node, Var))
	{
		Var		   *var = (Var *) node;

		if (var->varlevelsup == 0)
			result = bms_make_singleton(var->varno);
	}
	else if (IsA(node, List))
	{
		ListCell   *l;

		foreach(l, (List *) node)
		{
			result = bms_join(result, find_nonnullable_rels(lfirst(l),
															top_level));
		}
	}
	else if (IsA(node, FuncExpr))
	{
		FuncExpr   *expr = (FuncExpr *) node;

		if (func_strict(expr->funcid))
			result = find_nonnullable_rels((Node *) expr->args, false);
	}
	else if (IsA(node, OpExpr))
	{
		OpExpr	   *expr = (OpExpr *) node;

		if (op_strict(expr->opno))
			result = find_nonnullable_rels((Node *) expr->args, false);
	}
	else if (IsA(node, BoolExpr))
	{
		BoolExpr   *expr = (BoolExpr *) node;

		/* NOT is strict, others are not */
		if (expr->boolop == NOT_EXPR)
			result = find_nonnullable_rels((Node *) expr->args, false);
	}
	else if (IsA(node, RelabelType))
	{
		RelabelType *expr = (RelabelType *) node;

		result = find_nonnullable_rels((Node *) expr->arg, top_level);
	}
	else if (IsA(node, ConvertRowtypeExpr))
	{
		/* not clear this is useful, but it can't hurt */
		ConvertRowtypeExpr *expr = (ConvertRowtypeExpr *) node;

		result = find_nonnullable_rels((Node *) expr->arg, top_level);
	}
	else if (IsA(node, NullTest))
	{
		NullTest   *expr = (NullTest *) node;

		/*
		 * IS NOT NULL can be considered strict, but only at top level; else
		 * we might have something like NOT (x IS NOT NULL).
		 */
		if (top_level && expr->nulltesttype == IS_NOT_NULL)
			result = find_nonnullable_rels((Node *) expr->arg, false);
	}
	else if (IsA(node, BooleanTest))
	{
		BooleanTest *expr = (BooleanTest *) node;

		/*
		 * Appropriate boolean tests are strict at top level.
		 */
		if (top_level &&
			(expr->booltesttype == IS_TRUE ||
			 expr->booltesttype == IS_FALSE ||
			 expr->booltesttype == IS_NOT_UNKNOWN))
			result = find_nonnullable_rels((Node *) expr->arg, false);
	}
	return result;
}

/*
 * simplify_jointree
 *		Attempt to simplify a query's jointree.
 *
 * If we succeed in pulling up a subquery then we might form a jointree
 * in which a FromExpr is a direct child of another FromExpr.  In that
 * case we can consider collapsing the two FromExprs into one.	This is
 * an optional conversion, since the planner will work correctly either
 * way.  But we may find a better plan (at the cost of more planning time)
 * if we merge the two nodes, creating a single join search space out of
 * two.  To allow the user to trade off planning time against plan quality,
 * we provide a control parameter from_collapse_limit that limits the size
 * of the join search space that can be created this way.
 *
 * We also consider flattening explicit inner JOINs into FromExprs (which
 * will in turn allow them to be merged into parent FromExprs).  The tradeoffs
 * here are the same as for flattening FromExprs, but we use a different
 * control parameter so that the user can use explicit JOINs to control the
 * join order even when they are inner JOINs.
 *
 * NOTE: don't try to do this in the same jointree scan that does subquery
 * pullup!	Since we're changing the jointree structure here, that wouldn't
 * work reliably --- see comments for pull_up_subqueries().
 */
Node *
simplify_jointree(PlannerInfo *root, Node *jtnode)
{
	if (jtnode == NULL)
		return NULL;
	if (IsA(jtnode, RangeTblRef))
	{
		/* nothing to do here... */
	}
	else if (IsA(jtnode, FromExpr))
	{
		FromExpr   *f = (FromExpr *) jtnode;
		List	   *newlist = NIL;
		int			children_remaining;
		ListCell   *l;

		children_remaining = list_length(f->fromlist);
		foreach(l, f->fromlist)
		{
			Node	   *child = (Node *) lfirst(l);

			children_remaining--;
			/* Recursively simplify this child... */
			child = simplify_jointree(root, child);
			/* Now, is it a FromExpr? */
			if (child && IsA(child, FromExpr))
			{
				/*
				 * Yes, so do we want to merge it into parent?	Always do so
				 * if child has just one element (since that doesn't make the
				 * parent's list any longer).  Otherwise merge if the
				 * resulting join list would be no longer than
				 * from_collapse_limit.
				 */
				FromExpr   *subf = (FromExpr *) child;
				int			childlen = list_length(subf->fromlist);
				int			myothers = list_length(newlist) + children_remaining;

				if (childlen <= 1 ||
					(childlen + myothers) <= from_collapse_limit)
				{
					newlist = list_concat(newlist, subf->fromlist);

					/*
					 * By now, the quals have been converted to implicit-AND
					 * lists, so we just need to join the lists.  NOTE: we put
					 * the pulled-up quals first.
					 */
					f->quals = (Node *) list_concat((List *) subf->quals,
													(List *) f->quals);
				}
				else
					newlist = lappend(newlist, child);
			}
			else
				newlist = lappend(newlist, child);
		}
		f->fromlist = newlist;
	}
	else if (IsA(jtnode, JoinExpr))
	{
		JoinExpr   *j = (JoinExpr *) jtnode;

		/* Recursively simplify the children... */
		j->larg = simplify_jointree(root, j->larg);
		j->rarg = simplify_jointree(root, j->rarg);

		/*
		 * If it is an outer join, we must not flatten it.	An inner join is
		 * semantically equivalent to a FromExpr; we convert it to one,
		 * allowing it to be flattened into its parent, if the resulting
		 * FromExpr would have no more than join_collapse_limit members.
		 */
		if (j->jointype == JOIN_INNER && join_collapse_limit > 1)
		{
			int			leftlen,
						rightlen;

			if (j->larg && IsA(j->larg, FromExpr))
				leftlen = list_length(((FromExpr *) j->larg)->fromlist);
			else
				leftlen = 1;
			if (j->rarg && IsA(j->rarg, FromExpr))
				rightlen = list_length(((FromExpr *) j->rarg)->fromlist);
			else
				rightlen = 1;
			if ((leftlen + rightlen) <= join_collapse_limit)
			{
				FromExpr   *f = makeNode(FromExpr);

				f->fromlist = NIL;
				f->quals = NULL;

				if (j->larg && IsA(j->larg, FromExpr))
				{
					FromExpr   *subf = (FromExpr *) j->larg;

					f->fromlist = subf->fromlist;
					f->quals = subf->quals;
				}
				else
					f->fromlist = list_make1(j->larg);

				if (j->rarg && IsA(j->rarg, FromExpr))
				{
					FromExpr   *subf = (FromExpr *) j->rarg;

					f->fromlist = list_concat(f->fromlist,
											  subf->fromlist);
					f->quals = (Node *) list_concat((List *) f->quals,
													(List *) subf->quals);
				}
				else
					f->fromlist = lappend(f->fromlist, j->rarg);

				/* pulled-up quals first */
				f->quals = (Node *) list_concat((List *) f->quals,
												(List *) j->quals);

				return (Node *) f;
			}
		}
	}
	else
		elog(ERROR, "unrecognized node type: %d",
			 (int) nodeTag(jtnode));
	return jtnode;
}

/*
 * fix_in_clause_relids: update RT-index sets of InClauseInfo nodes
 *
 * When we pull up a subquery, any InClauseInfo references to the subquery's
 * RT index have to be replaced by the set of substituted relids.
 *
 * We assume we may modify the InClauseInfo nodes in-place.
 */
static void
fix_in_clause_relids(List *in_info_list, int varno, Relids subrelids)
{
	ListCell   *l;

	foreach(l, in_info_list)
	{
		InClauseInfo *ininfo = (InClauseInfo *) lfirst(l);

		if (bms_is_member(varno, ininfo->lefthand))
		{
			ininfo->lefthand = bms_del_member(ininfo->lefthand, varno);
			ininfo->lefthand = bms_add_members(ininfo->lefthand, subrelids);
		}
		if (bms_is_member(varno, ininfo->righthand))
		{
			ininfo->righthand = bms_del_member(ininfo->righthand, varno);
			ininfo->righthand = bms_add_members(ininfo->righthand, subrelids);
		}
	}
}

/*
 * get_relids_in_jointree: get set of base RT indexes present in a jointree
 */
Relids
get_relids_in_jointree(Node *jtnode)
{
	Relids		result = NULL;

	if (jtnode == NULL)
		return result;
	if (IsA(jtnode, RangeTblRef))
	{
		int			varno = ((RangeTblRef *) jtnode)->rtindex;

		result = bms_make_singleton(varno);
	}
	else if (IsA(jtnode, FromExpr))
	{
		FromExpr   *f = (FromExpr *) jtnode;
		ListCell   *l;

		foreach(l, f->fromlist)
		{
			result = bms_join(result,
							  get_relids_in_jointree(lfirst(l)));
		}
	}
	else if (IsA(jtnode, JoinExpr))
	{
		JoinExpr   *j = (JoinExpr *) jtnode;

		/* join's own RT index is not wanted in result */
		result = get_relids_in_jointree(j->larg);
		result = bms_join(result, get_relids_in_jointree(j->rarg));
	}
	else
		elog(ERROR, "unrecognized node type: %d",
			 (int) nodeTag(jtnode));
	return result;
}

/*
 * get_relids_for_join: get set of base RT indexes making up a join
 *
 * NB: this will not work reliably after simplify_jointree() is run,
 * since that may eliminate join nodes from the jointree.
 */
Relids
get_relids_for_join(PlannerInfo *root, int joinrelid)
{
	Node	   *jtnode;

	jtnode = find_jointree_node_for_rel((Node *) root->parse->jointree,
										joinrelid);
	if (!jtnode)
		elog(ERROR, "could not find join node %d", joinrelid);
	return get_relids_in_jointree(jtnode);
}

/*
 * find_jointree_node_for_rel: locate jointree node for a base or join RT index
 *
 * Returns NULL if not found
 */
static Node *
find_jointree_node_for_rel(Node *jtnode, int relid)
{
	if (jtnode == NULL)
		return NULL;
	if (IsA(jtnode, RangeTblRef))
	{
		int			varno = ((RangeTblRef *) jtnode)->rtindex;

		if (relid == varno)
			return jtnode;
	}
	else if (IsA(jtnode, FromExpr))
	{
		FromExpr   *f = (FromExpr *) jtnode;
		ListCell   *l;

		foreach(l, f->fromlist)
		{
			jtnode = find_jointree_node_for_rel(lfirst(l), relid);
			if (jtnode)
				return jtnode;
		}
	}
	else if (IsA(jtnode, JoinExpr))
	{
		JoinExpr   *j = (JoinExpr *) jtnode;

		if (relid == j->rtindex)
			return jtnode;
		jtnode = find_jointree_node_for_rel(j->larg, relid);
		if (jtnode)
			return jtnode;
		jtnode = find_jointree_node_for_rel(j->rarg, relid);
		if (jtnode)
			return jtnode;
	}
	else
		elog(ERROR, "unrecognized node type: %d",
			 (int) nodeTag(jtnode));
	return NULL;
}