initsplan.c

来自「postgresql8.3.4源码,开源数据库」· C语言 代码 · 共 1,362 行 · 第 1/4 页

/*
 * check_outerjoin_delay
 *		Detect whether a qual referencing the given relids must be delayed
 *		in application due to the presence of a lower outer join, and/or
 *		may force extra delay of higher-level outer joins.
 *
 * If the qual must be delayed, add relids to *relids_p to reflect the lowest
 * safe level for evaluating the qual, and return TRUE.  Any extra delay for
 * higher-level joins is reflected by setting delay_upper_joins to TRUE in
 * OuterJoinInfo structs.
 *
 * For an is_pushed_down qual, we can evaluate the qual as soon as (1) we have
 * all the rels it mentions, and (2) we are at or above any outer joins that
 * can null any of these rels and are below the syntactic location of the
 * given qual.	We must enforce (2) because pushing down such a clause below
 * the OJ might cause the OJ to emit null-extended rows that should not have
 * been formed, or that should have been rejected by the clause.  (This is
 * only an issue for non-strict quals, since if we can prove a qual mentioning
 * only nullable rels is strict, we'd have reduced the outer join to an inner
 * join in reduce_outer_joins().)
 *
 * To enforce (2), scan the oj_info_list and merge the required-relid sets of
 * any such OJs into the clause's own reference list.  At the time we are
 * called, the oj_info_list contains only outer joins below this qual.	We
 * have to repeat the scan until no new relids get added; this ensures that
 * the qual is suitably delayed regardless of the order in which OJs get
 * executed.  As an example, if we have one OJ with LHS=A, RHS=B, and one with
 * LHS=B, RHS=C, it is implied that these can be done in either order; if the
 * B/C join is done first then the join to A can null C, so a qual actually
 * mentioning only C cannot be applied below the join to A.
 *
 * For a non-pushed-down qual, this isn't going to determine where we place the
 * qual, but we need to determine outerjoin_delayed anyway for possible use
 * in reconsider_outer_join_clauses().
 *
 * Lastly, a pushed-down qual that references the nullable side of any current
 * oj_info_list member and has to be evaluated above that OJ (because its
 * required relids overlap the LHS too) causes that OJ's delay_upper_joins
 * flag to be set TRUE.  This will prevent any higher-level OJs from
 * being interchanged with that OJ, which would result in not having any
 * correct place to evaluate the qual.	(The case we care about here is a
 * sub-select WHERE clause within the RHS of some outer join.  The WHERE
 * clause must effectively be treated as a degenerate clause of that outer
 * join's condition.  Rather than trying to match such clauses with joins
 * directly, we set delay_upper_joins here, and when the upper outer join
 * is processed by make_outerjoininfo, it will refrain from allowing the
 * two OJs to commute.)
 */
static bool
check_outerjoin_delay(PlannerInfo *root, Relids *relids_p,
					  bool is_pushed_down)
{
	Relids		relids = *relids_p;
	bool		outerjoin_delayed;
	bool		found_some;

	outerjoin_delayed = false;
	do
	{
		ListCell   *l;

		found_some = false;
		foreach(l, root->oj_info_list)
		{
			OuterJoinInfo *ojinfo = (OuterJoinInfo *) lfirst(l);

			/* do we reference any nullable rels of this OJ? */
			if (bms_overlap(relids, ojinfo->min_righthand) ||
				(ojinfo->is_full_join &&
				 bms_overlap(relids, ojinfo->min_lefthand)))
			{
				/* yes, so set the result flag */
				outerjoin_delayed = true;
				/* have we included all its rels in relids? */
				if (!bms_is_subset(ojinfo->min_lefthand, relids) ||
					!bms_is_subset(ojinfo->min_righthand, relids))
				{
					/* no, so add them in */
					relids = bms_add_members(relids, ojinfo->min_lefthand);
					relids = bms_add_members(relids, ojinfo->min_righthand);
					/* we'll need another iteration */
					found_some = true;
				}
				/* set delay_upper_joins if needed */
				if (is_pushed_down && !ojinfo->is_full_join &&
					bms_overlap(relids, ojinfo->min_lefthand))
					ojinfo->delay_upper_joins = true;
			}
		}
	} while (found_some);

	*relids_p = relids;
	return outerjoin_delayed;
}

/*
 * distribute_restrictinfo_to_rels
 *	  Push a completed RestrictInfo into the proper restriction or join
 *	  clause list(s).
 *
 * This is the last step of distribute_qual_to_rels() for ordinary qual
 * clauses.  Clauses that are interesting for equivalence-class processing
 * are diverted to the EC machinery, but may ultimately get fed back here.
 */
void
distribute_restrictinfo_to_rels(PlannerInfo *root,
								RestrictInfo *restrictinfo)
{
	Relids		relids = restrictinfo->required_relids;
	RelOptInfo *rel;

	switch (bms_membership(relids))
	{
		case BMS_SINGLETON:

			/*
			 * There is only one relation participating in the clause, so it
			 * is a restriction clause for that relation.
			 */
			rel = find_base_rel(root, bms_singleton_member(relids));

			/* Add clause to rel's restriction list */
			rel->baserestrictinfo = lappend(rel->baserestrictinfo,
											restrictinfo);
			break;
		case BMS_MULTIPLE:

			/*
			 * The clause is a join clause, since there is more than one rel
			 * in its relid set.
			 */

			/*
			 * Check for hashjoinable operators.  (We don't bother setting the
			 * hashjoin info if we're not going to need it.)
			 */
			if (enable_hashjoin)
				check_hashjoinable(restrictinfo);

			/*
			 * Add clause to the join lists of all the relevant relations.
			 */
			add_join_clause_to_rels(root, restrictinfo, relids);
			break;
		default:

			/*
			 * clause references no rels, and therefore we have no place to
			 * attach it.  Shouldn't get here if callers are working properly.
			 */
			elog(ERROR, "cannot cope with variable-free clause");
			break;
	}
}

/*
 * process_implied_equality
 *	  Create a restrictinfo item that says "item1 op item2", and push it
 *	  into the appropriate lists.  (In practice opno is always a btree
 *	  equality operator.)
 *
 * "qualscope" is the nominal syntactic level to impute to the restrictinfo.
 * This must contain at least all the rels used in the expressions, but it
 * is used only to set the qual application level when both exprs are
 * variable-free.  Otherwise the qual is applied at the lowest join level
 * that provides all its variables.
 *
 * "both_const" indicates whether both items are known pseudo-constant;
 * in this case it is worth applying eval_const_expressions() in case we
 * can produce constant TRUE or constant FALSE.  (Otherwise it's not,
 * because the expressions went through eval_const_expressions already.)
 *
 * This is currently used only when an EquivalenceClass is found to
 * contain pseudoconstants.  See path/pathkeys.c for more details.
 */
void
process_implied_equality(PlannerInfo *root,
						 Oid opno,
						 Expr *item1,
						 Expr *item2,
						 Relids qualscope,
						 bool below_outer_join,
						 bool both_const)
{
	Expr	   *clause;

	/*
	 * Build the new clause.  Copy to ensure it shares no substructure with
	 * original (this is necessary in case there are subselects in there...)
	 */
	clause = make_opclause(opno,
						   BOOLOID,		/* opresulttype */
						   false,		/* opretset */
						   (Expr *) copyObject(item1),
						   (Expr *) copyObject(item2));

	/* If both constant, try to reduce to a boolean constant. */
	if (both_const)
	{
		clause = (Expr *) eval_const_expressions(root, (Node *) clause);

		/* If we produced const TRUE, just drop the clause */
		if (clause && IsA(clause, Const))
		{
			Const	   *cclause = (Const *) clause;

			Assert(cclause->consttype == BOOLOID);
			if (!cclause->constisnull && DatumGetBool(cclause->constvalue))
				return;
		}
	}

	/* Make a copy of qualscope to avoid problems if source EC changes */
	qualscope = bms_copy(qualscope);

	/*
	 * Push the new clause into all the appropriate restrictinfo lists.
	 */
	distribute_qual_to_rels(root, (Node *) clause,
							true, below_outer_join,
							qualscope, NULL, NULL);
}

/*
 * build_implied_join_equality --- build a RestrictInfo for a derived equality
 *
 * This overlaps the functionality of process_implied_equality(), but we
 * must return the RestrictInfo, not push it into the joininfo tree.
 */
RestrictInfo *
build_implied_join_equality(Oid opno,
							Expr *item1,
							Expr *item2,
							Relids qualscope)
{
	RestrictInfo *restrictinfo;
	Expr	   *clause;

	/*
	 * Build the new clause.  Copy to ensure it shares no substructure with
	 * original (this is necessary in case there are subselects in there...)
	 */
	clause = make_opclause(opno,
						   BOOLOID,		/* opresulttype */
						   false,		/* opretset */
						   (Expr *) copyObject(item1),
						   (Expr *) copyObject(item2));

	/* Make a copy of qualscope to avoid problems if source EC changes */
	qualscope = bms_copy(qualscope);

	/*
	 * Build the RestrictInfo node itself.
	 */
	restrictinfo = make_restrictinfo(clause,
									 true,		/* is_pushed_down */
									 false,		/* outerjoin_delayed */
									 false,		/* pseudoconstant */
									 qualscope);

	/* Set mergejoinability info always, and hashjoinability if enabled */
	check_mergejoinable(restrictinfo);
	if (enable_hashjoin)
		check_hashjoinable(restrictinfo);

	return restrictinfo;
}


/*****************************************************************************
 *
 *	 CHECKS FOR MERGEJOINABLE AND HASHJOINABLE CLAUSES
 *
 *****************************************************************************/

/*
 * check_mergejoinable
 *	  If the restrictinfo's clause is mergejoinable, set the mergejoin
 *	  info fields in the restrictinfo.
 *
 *	  Currently, we support mergejoin for binary opclauses where
 *	  the operator is a mergejoinable operator.  The arguments can be
 *	  anything --- as long as there are no volatile functions in them.
 */
static void
check_mergejoinable(RestrictInfo *restrictinfo)
{
	Expr	   *clause = restrictinfo->clause;
	Oid			opno;

	if (restrictinfo->pseudoconstant)
		return;
	if (!is_opclause(clause))
		return;
	if (list_length(((OpExpr *) clause)->args) != 2)
		return;

	opno = ((OpExpr *) clause)->opno;

	if (op_mergejoinable(opno) &&
		!contain_volatile_functions((Node *) clause))
		restrictinfo->mergeopfamilies = get_mergejoin_opfamilies(opno);

	/*
	 * Note: op_mergejoinable is just a hint; if we fail to find the operator
	 * in any btree opfamilies, mergeopfamilies remains NIL and so the clause
	 * is not treated as mergejoinable.
	 */
}

/*
 * check_hashjoinable
 *	  If the restrictinfo's clause is hashjoinable, set the hashjoin
 *	  info fields in the restrictinfo.
 *
 *	  Currently, we support hashjoin for binary opclauses where
 *	  the operator is a hashjoinable operator.	The arguments can be
 *	  anything --- as long as there are no volatile functions in them.
 */
static void
check_hashjoinable(RestrictInfo *restrictinfo)
{
	Expr	   *clause = restrictinfo->clause;
	Oid			opno;

	if (restrictinfo->pseudoconstant)
		return;
	if (!is_opclause(clause))
		return;
	if (list_length(((OpExpr *) clause)->args) != 2)
		return;

	opno = ((OpExpr *) clause)->opno;

	if (op_hashjoinable(opno) &&
		!contain_volatile_functions((Node *) clause))
		restrictinfo->hashjoinoperator = opno;
}