restrictinfo.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

	restrictinfo->eval_cost.startup = -1;
	restrictinfo->this_selec = -1;

	restrictinfo->mergejoinoperator = InvalidOid;
	restrictinfo->left_sortop = InvalidOid;
	restrictinfo->right_sortop = InvalidOid;

	restrictinfo->left_pathkey = NIL;
	restrictinfo->right_pathkey = NIL;

	restrictinfo->left_mergescansel = -1;
	restrictinfo->right_mergescansel = -1;

	restrictinfo->hashjoinoperator = InvalidOid;

	restrictinfo->left_bucketsize = -1;
	restrictinfo->right_bucketsize = -1;

	return restrictinfo;
}

/*
 * Recursively insert sub-RestrictInfo nodes into a boolean expression.
 *
 * We put RestrictInfos above simple (non-AND/OR) clauses and above
 * sub-OR clauses, but not above sub-AND clauses, because there's no need.
 * This may seem odd but it is closely related to the fact that we use
 * implicit-AND lists at top level of RestrictInfo lists.  Only ORs and
 * simple clauses are valid RestrictInfos.
 *
 * The given required_relids are attached to our top-level output,
 * but any OR-clause constituents are allowed to default to just the
 * contained rels.
 */
static Expr *
make_sub_restrictinfos(Expr *clause,
					   bool is_pushed_down, bool outerjoin_delayed,
					   Relids required_relids)
{
	if (or_clause((Node *) clause))
	{
		List	   *orlist = NIL;
		ListCell   *temp;

		foreach(temp, ((BoolExpr *) clause)->args)
			orlist = lappend(orlist,
							 make_sub_restrictinfos(lfirst(temp),
													is_pushed_down,
													outerjoin_delayed,
													NULL));
		return (Expr *) make_restrictinfo_internal(clause,
												   make_orclause(orlist),
												   is_pushed_down,
												   outerjoin_delayed,
												   required_relids);
	}
	else if (and_clause((Node *) clause))
	{
		List	   *andlist = NIL;
		ListCell   *temp;

		foreach(temp, ((BoolExpr *) clause)->args)
			andlist = lappend(andlist,
							  make_sub_restrictinfos(lfirst(temp),
													 is_pushed_down,
													 outerjoin_delayed,
													 required_relids));
		return make_andclause(andlist);
	}
	else
		return (Expr *) make_restrictinfo_internal(clause,
												   NULL,
												   is_pushed_down,
												   outerjoin_delayed,
												   required_relids);
}

/*
 * restriction_is_or_clause
 *
 * Returns t iff the restrictinfo node contains an 'or' clause.
 */
bool
restriction_is_or_clause(RestrictInfo *restrictinfo)
{
	if (restrictinfo->orclause != NULL)
		return true;
	else
		return false;
}

/*
 * get_actual_clauses
 *
 * Returns a list containing the bare clauses from 'restrictinfo_list'.
 */
List *
get_actual_clauses(List *restrictinfo_list)
{
	List	   *result = NIL;
	ListCell   *temp;

	foreach(temp, restrictinfo_list)
	{
		RestrictInfo *rinfo = (RestrictInfo *) lfirst(temp);

		Assert(IsA(rinfo, RestrictInfo));

		result = lappend(result, rinfo->clause);
	}
	return result;
}

/*
 * get_actual_join_clauses
 *
 * Extract clauses from 'restrictinfo_list', separating those that
 * syntactically match the join level from those that were pushed down.
 */
void
get_actual_join_clauses(List *restrictinfo_list,
						List **joinquals, List **otherquals)
{
	ListCell   *temp;

	*joinquals = NIL;
	*otherquals = NIL;

	foreach(temp, restrictinfo_list)
	{
		RestrictInfo *clause = (RestrictInfo *) lfirst(temp);

		if (clause->is_pushed_down)
			*otherquals = lappend(*otherquals, clause->clause);
		else
			*joinquals = lappend(*joinquals, clause->clause);
	}
}

/*
 * remove_redundant_join_clauses
 *
 * Given a list of RestrictInfo clauses that are to be applied in a join,
 * remove any duplicate or redundant clauses.
 *
 * We must eliminate duplicates when forming the restrictlist for a joinrel,
 * since we will see many of the same clauses arriving from both input
 * relations. Also, if a clause is a mergejoinable clause, it's possible that
 * it is redundant with previous clauses (see optimizer/README for
 * discussion). We detect that case and omit the redundant clause from the
 * result list.
 *
 * The result is a fresh List, but it points to the same member nodes
 * as were in the input.
 */
List *
remove_redundant_join_clauses(PlannerInfo *root, List *restrictinfo_list,
							  bool isouterjoin)
{
	List	   *result = NIL;
	ListCell   *item;
	QualCost	cost;

	/*
	 * If there are any redundant clauses, we want to eliminate the ones that
	 * are more expensive in favor of the ones that are less so. Run
	 * cost_qual_eval() to ensure the eval_cost fields are set up.
	 */
	cost_qual_eval(&cost, restrictinfo_list);

	/*
	 * We don't have enough knowledge yet to be able to estimate the number of
	 * times a clause might be evaluated, so it's hard to weight the startup
	 * and per-tuple costs appropriately.  For now just weight 'em the same.
	 */
#define CLAUSECOST(r)  ((r)->eval_cost.startup + (r)->eval_cost.per_tuple)

	foreach(item, restrictinfo_list)
	{
		RestrictInfo *rinfo = (RestrictInfo *) lfirst(item);
		RestrictInfo *prevrinfo;

		/* is it redundant with any prior clause? */
		prevrinfo = join_clause_is_redundant(root, rinfo, result, isouterjoin);
		if (prevrinfo == NULL)
		{
			/* no, so add it to result list */
			result = lappend(result, rinfo);
		}
		else if (CLAUSECOST(rinfo) < CLAUSECOST(prevrinfo))
		{
			/* keep this one, drop the previous one */
			result = list_delete_ptr(result, prevrinfo);
			result = lappend(result, rinfo);
		}
		/* else, drop this one */
	}

	return result;
}

/*
 * select_nonredundant_join_clauses
 *
 * Given a list of RestrictInfo clauses that are to be applied in a join,
 * select the ones that are not redundant with any clause in the
 * reference_list.
 *
 * This is similar to remove_redundant_join_clauses, but we are looking for
 * redundancies with a separate list of clauses (i.e., clauses that have
 * already been applied below the join itself).
 *
 * Note that we assume the given restrictinfo_list has already been checked
 * for local redundancies, so we don't check again.
 */
List *
select_nonredundant_join_clauses(PlannerInfo *root,
								 List *restrictinfo_list,
								 List *reference_list,
								 bool isouterjoin)
{
	List	   *result = NIL;
	ListCell   *item;

	foreach(item, restrictinfo_list)
	{
		RestrictInfo *rinfo = (RestrictInfo *) lfirst(item);

		/* drop it if redundant with any reference clause */
		if (join_clause_is_redundant(root, rinfo, reference_list, isouterjoin) != NULL)
			continue;

		/* otherwise, add it to result list */
		result = lappend(result, rinfo);
	}

	return result;
}

/*
 * join_clause_is_redundant
 *		If rinfo is redundant with any clause in reference_list,
 *		return one such clause; otherwise return NULL.
 *
 * This is the guts of both remove_redundant_join_clauses and
 * select_nonredundant_join_clauses.  See the docs above for motivation.
 *
 * We can detect redundant mergejoinable clauses very cheaply by using their
 * left and right pathkeys, which uniquely identify the sets of equijoined
 * variables in question.  All the members of a pathkey set that are in the
 * left relation have already been forced to be equal; likewise for those in
 * the right relation.	So, we need to have only one clause that checks
 * equality between any set member on the left and any member on the right;
 * by transitivity, all the rest are then equal.
 *
 * However, clauses that are of the form "var expr = const expr" cannot be
 * eliminated as redundant.  This is because when there are const expressions
 * in a pathkey set, generate_implied_equalities() suppresses "var = var"
 * clauses in favor of "var = const" clauses.  We cannot afford to drop any
 * of the latter, even though they might seem redundant by the pathkey
 * membership test.
 *
 * Weird special case: if we have two clauses that seem redundant
 * except one is pushed down into an outer join and the other isn't,
 * then they're not really redundant, because one constrains the
 * joined rows after addition of null fill rows, and the other doesn't.
 */
static RestrictInfo *
join_clause_is_redundant(PlannerInfo *root,
						 RestrictInfo *rinfo,
						 List *reference_list,
						 bool isouterjoin)
{
	ListCell   *refitem;

	/* always consider exact duplicates redundant */
	foreach(refitem, reference_list)
	{
		RestrictInfo *refrinfo = (RestrictInfo *) lfirst(refitem);

		if (equal(rinfo, refrinfo))
			return refrinfo;
	}

	/* check for redundant merge clauses */
	if (rinfo->mergejoinoperator != InvalidOid)
	{
		/* do the cheap test first: is it a "var = const" clause? */
		if (bms_is_empty(rinfo->left_relids) ||
			bms_is_empty(rinfo->right_relids))
			return NULL;		/* var = const, so not redundant */

		cache_mergeclause_pathkeys(root, rinfo);

		foreach(refitem, reference_list)
		{
			RestrictInfo *refrinfo = (RestrictInfo *) lfirst(refitem);

			if (refrinfo->mergejoinoperator != InvalidOid)
			{
				cache_mergeclause_pathkeys(root, refrinfo);

				if (rinfo->left_pathkey == refrinfo->left_pathkey &&
					rinfo->right_pathkey == refrinfo->right_pathkey &&
					(rinfo->is_pushed_down == refrinfo->is_pushed_down ||
					 !isouterjoin))
				{
					/* Yup, it's redundant */
					return refrinfo;
				}
			}
		}
	}

	/* otherwise, not redundant */
	return NULL;
}