joinpath.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

			 * Always consider a nestloop join with this outer and
			 * cheapest-total-cost inner.  When appropriate, also consider
			 * using the materialized form of the cheapest inner, the
			 * cheapest-startup-cost inner path, and the best innerjoin
			 * indexpath.
			 */
			add_path(joinrel, (Path *)
					 create_nestloop_path(root,
										  joinrel,
										  jointype,
										  outerpath,
										  inner_cheapest_total,
										  restrictlist,
										  merge_pathkeys));
			if (matpath != NULL)
				add_path(joinrel, (Path *)
						 create_nestloop_path(root,
											  joinrel,
											  jointype,
											  outerpath,
											  matpath,
											  restrictlist,
											  merge_pathkeys));
			if (inner_cheapest_startup != inner_cheapest_total)
				add_path(joinrel, (Path *)
						 create_nestloop_path(root,
											  joinrel,
											  jointype,
											  outerpath,
											  inner_cheapest_startup,
											  restrictlist,
											  merge_pathkeys));
			if (bestinnerjoin != NULL)
				add_path(joinrel, (Path *)
						 create_nestloop_path(root,
											  joinrel,
											  jointype,
											  outerpath,
											  bestinnerjoin,
											  restrictlist,
											  merge_pathkeys));
		}

		/* Can't do anything else if outer path needs to be unique'd */
		if (save_jointype == JOIN_UNIQUE_OUTER)
			continue;

		/* Look for useful mergeclauses (if any) */
		mergeclauses = find_mergeclauses_for_pathkeys(root,
													  outerpath->pathkeys,
													  mergeclause_list);

		/*
		 * Done with this outer path if no chance for a mergejoin.
		 *
		 * Special corner case: for "x FULL JOIN y ON true", there will be no
		 * join clauses at all.  Ordinarily we'd generate a clauseless
		 * nestloop path, but since mergejoin is our only join type that
		 * supports FULL JOIN, it's necessary to generate a clauseless
		 * mergejoin path instead.
		 */
		if (mergeclauses == NIL)
		{
			if (jointype == JOIN_FULL)
				 /* okay to try for mergejoin */ ;
			else
				continue;
		}
		if (useallclauses && list_length(mergeclauses) != list_length(mergeclause_list))
			continue;

		/* Compute the required ordering of the inner path */
		innersortkeys = make_pathkeys_for_mergeclauses(root,
													   mergeclauses,
													   innerrel);

		/*
		 * Generate a mergejoin on the basis of sorting the cheapest inner.
		 * Since a sort will be needed, only cheapest total cost matters. (But
		 * create_mergejoin_path will do the right thing if
		 * inner_cheapest_total is already correctly sorted.)
		 */
		add_path(joinrel, (Path *)
				 create_mergejoin_path(root,
									   joinrel,
									   jointype,
									   outerpath,
									   inner_cheapest_total,
									   restrictlist,
									   merge_pathkeys,
									   mergeclauses,
									   NIL,
									   innersortkeys));

		/* Can't do anything else if inner path needs to be unique'd */
		if (save_jointype == JOIN_UNIQUE_INNER)
			continue;

		/*
		 * Look for presorted inner paths that satisfy the innersortkey list
		 * --- or any truncation thereof, if we are allowed to build a
		 * mergejoin using a subset of the merge clauses.  Here, we consider
		 * both cheap startup cost and cheap total cost.  Ignore
		 * inner_cheapest_total, since we already made a path with it.
		 */
		num_sortkeys = list_length(innersortkeys);
		if (num_sortkeys > 1 && !useallclauses)
			trialsortkeys = list_copy(innersortkeys);	/* need modifiable copy */
		else
			trialsortkeys = innersortkeys;		/* won't really truncate */
		cheapest_startup_inner = NULL;
		cheapest_total_inner = NULL;

		for (sortkeycnt = num_sortkeys; sortkeycnt > 0; sortkeycnt--)
		{
			Path	   *innerpath;
			List	   *newclauses = NIL;

			/*
			 * Look for an inner path ordered well enough for the first
			 * 'sortkeycnt' innersortkeys.	NB: trialsortkeys list is modified
			 * destructively, which is why we made a copy...
			 */
			trialsortkeys = list_truncate(trialsortkeys, sortkeycnt);
			innerpath = get_cheapest_path_for_pathkeys(innerrel->pathlist,
													   trialsortkeys,
													   TOTAL_COST);
			if (innerpath != NULL &&
				innerpath != inner_cheapest_total &&
				(cheapest_total_inner == NULL ||
				 compare_path_costs(innerpath, cheapest_total_inner,
									TOTAL_COST) < 0))
			{
				/* Found a cheap (or even-cheaper) sorted path */
				/* Select the right mergeclauses, if we didn't already */
				if (sortkeycnt < num_sortkeys)
				{
					newclauses =
						find_mergeclauses_for_pathkeys(root,
													   trialsortkeys,
													   mergeclauses);
					Assert(newclauses != NIL);
				}
				else
					newclauses = mergeclauses;
				add_path(joinrel, (Path *)
						 create_mergejoin_path(root,
											   joinrel,
											   jointype,
											   outerpath,
											   innerpath,
											   restrictlist,
											   merge_pathkeys,
											   newclauses,
											   NIL,
											   NIL));
				cheapest_total_inner = innerpath;
			}
			/* Same on the basis of cheapest startup cost ... */
			innerpath = get_cheapest_path_for_pathkeys(innerrel->pathlist,
													   trialsortkeys,
													   STARTUP_COST);
			if (innerpath != NULL &&
				innerpath != inner_cheapest_total &&
				(cheapest_startup_inner == NULL ||
				 compare_path_costs(innerpath, cheapest_startup_inner,
									STARTUP_COST) < 0))
			{
				/* Found a cheap (or even-cheaper) sorted path */
				if (innerpath != cheapest_total_inner)
				{
					/*
					 * Avoid rebuilding clause list if we already made one;
					 * saves memory in big join trees...
					 */
					if (newclauses == NIL)
					{
						if (sortkeycnt < num_sortkeys)
						{
							newclauses =
								find_mergeclauses_for_pathkeys(root,
															   trialsortkeys,
															   mergeclauses);
							Assert(newclauses != NIL);
						}
						else
							newclauses = mergeclauses;
					}
					add_path(joinrel, (Path *)
							 create_mergejoin_path(root,
												   joinrel,
												   jointype,
												   outerpath,
												   innerpath,
												   restrictlist,
												   merge_pathkeys,
												   newclauses,
												   NIL,
												   NIL));
				}
				cheapest_startup_inner = innerpath;
			}

			/*
			 * Don't consider truncated sortkeys if we need all clauses.
			 */
			if (useallclauses)
				break;
		}
	}
}

/*
 * hash_inner_and_outer
 *	  Create hashjoin join paths by explicitly hashing both the outer and
 *	  inner keys of each available hash clause.
 *
 * 'joinrel' is the join relation
 * 'outerrel' is the outer join relation
 * 'innerrel' is the inner join relation
 * 'restrictlist' contains all of the RestrictInfo nodes for restriction
 *		clauses that apply to this join
 * 'jointype' is the type of join to do
 */
static void
hash_inner_and_outer(PlannerInfo *root,
					 RelOptInfo *joinrel,
					 RelOptInfo *outerrel,
					 RelOptInfo *innerrel,
					 List *restrictlist,
					 JoinType jointype)
{
	bool		isouterjoin;
	List	   *hashclauses;
	ListCell   *l;

	/*
	 * Hashjoin only supports inner, left, and IN joins.
	 */
	switch (jointype)
	{
		case JOIN_INNER:
		case JOIN_IN:
		case JOIN_UNIQUE_OUTER:
		case JOIN_UNIQUE_INNER:
			isouterjoin = false;
			break;
		case JOIN_LEFT:
			isouterjoin = true;
			break;
		default:
			return;
	}

	/*
	 * We need to build only one hashpath for any given pair of outer and
	 * inner relations; all of the hashable clauses will be used as keys.
	 *
	 * Scan the join's restrictinfo list to find hashjoinable clauses that are
	 * usable with this pair of sub-relations.
	 */
	hashclauses = NIL;
	foreach(l, restrictlist)
	{
		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(l);

		if (!restrictinfo->can_join ||
			restrictinfo->hashjoinoperator == InvalidOid)
			continue;			/* not hashjoinable */

		/*
		 * If processing an outer join, only use its own join clauses for
		 * hashing.  For inner joins we need not be so picky.
		 */
		if (isouterjoin && restrictinfo->is_pushed_down)
			continue;

		/*
		 * Check if clause is usable with these input rels.
		 */
		if (bms_is_subset(restrictinfo->left_relids, outerrel->relids) &&
			bms_is_subset(restrictinfo->right_relids, innerrel->relids))
		{
			/* righthand side is inner */
		}
		else if (bms_is_subset(restrictinfo->left_relids, innerrel->relids) &&
				 bms_is_subset(restrictinfo->right_relids, outerrel->relids))
		{
			/* lefthand side is inner */
		}
		else
			continue;			/* no good for these input relations */

		hashclauses = lappend(hashclauses, restrictinfo);
	}

	/* If we found any usable hashclauses, make a path */
	if (hashclauses)
	{
		/*
		 * We consider both the cheapest-total-cost and cheapest-startup-cost
		 * outer paths.  There's no need to consider any but the
		 * cheapest-total-cost inner path, however.
		 */
		Path	   *cheapest_startup_outer = outerrel->cheapest_startup_path;
		Path	   *cheapest_total_outer = outerrel->cheapest_total_path;
		Path	   *cheapest_total_inner = innerrel->cheapest_total_path;

		/* Unique-ify if need be */
		if (jointype == JOIN_UNIQUE_OUTER)
		{
			cheapest_total_outer = (Path *)
				create_unique_path(root, outerrel, cheapest_total_outer);
			cheapest_startup_outer = cheapest_total_outer;
			jointype = JOIN_INNER;
		}
		else if (jointype == JOIN_UNIQUE_INNER)
		{
			cheapest_total_inner = (Path *)
				create_unique_path(root, innerrel, cheapest_total_inner);
			jointype = JOIN_INNER;
		}

		add_path(joinrel, (Path *)
				 create_hashjoin_path(root,
									  joinrel,
									  jointype,
									  cheapest_total_outer,
									  cheapest_total_inner,
									  restrictlist,
									  hashclauses));
		if (cheapest_startup_outer != cheapest_total_outer)
			add_path(joinrel, (Path *)
					 create_hashjoin_path(root,
										  joinrel,
										  jointype,
										  cheapest_startup_outer,
										  cheapest_total_inner,
										  restrictlist,
										  hashclauses));
	}
}

/*
 * select_mergejoin_clauses
 *	  Select mergejoin clauses that are usable for a particular join.
 *	  Returns a list of RestrictInfo nodes for those clauses.
 *
 * We examine each restrictinfo clause known for the join to see
 * if it is mergejoinable and involves vars from the two sub-relations
 * currently of interest.
 */
static List *
select_mergejoin_clauses(RelOptInfo *joinrel,
						 RelOptInfo *outerrel,
						 RelOptInfo *innerrel,
						 List *restrictlist,
						 JoinType jointype)
{
	List	   *result_list = NIL;
	bool		isouterjoin = IS_OUTER_JOIN(jointype);
	bool		have_nonmergeable_joinclause = false;
	ListCell   *l;

	foreach(l, restrictlist)
	{
		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(l);

		/*
		 * If processing an outer join, only use its own join clauses in the
		 * merge.  For inner joins we can use pushed-down clauses too. (Note:
		 * we don't set have_nonmergeable_joinclause here because pushed-down
		 * clauses will become otherquals not joinquals.)
		 */
		if (isouterjoin && restrictinfo->is_pushed_down)
			continue;

		if (!restrictinfo->can_join ||
			restrictinfo->mergejoinoperator == InvalidOid)
		{
			have_nonmergeable_joinclause = true;
			continue;			/* not mergejoinable */
		}

		/*
		 * Check if clause is usable with these input rels.  All the vars
		 * needed on each side of the clause must be available from one or the
		 * other of the input rels.
		 */
		if (bms_is_subset(restrictinfo->left_relids, outerrel->relids) &&
			bms_is_subset(restrictinfo->right_relids, innerrel->relids))
		{
			/* righthand side is inner */
		}
		else if (bms_is_subset(restrictinfo->left_relids, innerrel->relids) &&
				 bms_is_subset(restrictinfo->right_relids, outerrel->relids))
		{
			/* lefthand side is inner */
		}
		else
		{
			have_nonmergeable_joinclause = true;
			continue;			/* no good for these input relations */
		}

		result_list = lcons(restrictinfo, result_list);
	}

	/*
	 * If it is a right/full join then *all* the explicit join clauses must be
	 * mergejoinable, else the executor will fail. If we are asked for a right
	 * join then just return NIL to indicate no mergejoin is possible (we can
	 * handle it as a left join instead). If we are asked for a full join then
	 * emit an error, because there is no fallback.
	 */
	if (have_nonmergeable_joinclause)
	{
		switch (jointype)
		{
			case JOIN_RIGHT:
				return NIL;		/* not mergejoinable */
			case JOIN_FULL:
				ereport(ERROR,
						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						 errmsg("FULL JOIN is only supported with merge-joinable join conditions")));
				break;
			default:
				/* otherwise, it's OK to have nonmergeable join quals */
				break;
		}
	}

	return result_list;
}