pathnode.c

来自「PostgreSQL7.4.6 for Linux」· C语言 代码 · 共 863 行 · 第 1/2 页

	{
		Path	   *subpath = (Path *) lfirst(l);

		if (l == subpaths)		/* first node? */
			pathnode->path.startup_cost = subpath->startup_cost;
		pathnode->path.total_cost += subpath->total_cost;
	}

	return pathnode;
}

/*
 * create_result_path
 *	  Creates a path corresponding to a Result plan, returning the
 *	  pathnode.
 */
ResultPath *
create_result_path(RelOptInfo *rel, Path *subpath, List *constantqual)
{
	ResultPath *pathnode = makeNode(ResultPath);

	pathnode->path.pathtype = T_Result;
	pathnode->path.parent = rel;	/* may be NULL */

	if (subpath)
		pathnode->path.pathkeys = subpath->pathkeys;
	else
		pathnode->path.pathkeys = NIL;

	pathnode->subpath = subpath;
	pathnode->constantqual = constantqual;

	/* Ideally should define cost_result(), but I'm too lazy */
	if (subpath)
	{
		pathnode->path.startup_cost = subpath->startup_cost;
		pathnode->path.total_cost = subpath->total_cost;
	}
	else
	{
		pathnode->path.startup_cost = 0;
		pathnode->path.total_cost = cpu_tuple_cost;
	}

	return pathnode;
}

/*
 * create_material_path
 *	  Creates a path corresponding to a Material plan, returning the
 *	  pathnode.
 */
MaterialPath *
create_material_path(RelOptInfo *rel, Path *subpath)
{
	MaterialPath *pathnode = makeNode(MaterialPath);

	pathnode->path.pathtype = T_Material;
	pathnode->path.parent = rel;

	pathnode->path.pathkeys = subpath->pathkeys;

	pathnode->subpath = subpath;

	cost_material(&pathnode->path,
				  subpath->total_cost,
				  rel->rows,
				  rel->width);

	return pathnode;
}

/*
 * create_unique_path
 *	  Creates a path representing elimination of distinct rows from the
 *	  input data.
 *
 * If used at all, this is likely to be called repeatedly on the same rel;
 * and the input subpath should always be the same (the cheapest_total path
 * for the rel).  So we cache the result.
 */
UniquePath *
create_unique_path(Query *root, RelOptInfo *rel, Path *subpath)
{
	UniquePath *pathnode;
	Path		sort_path;		/* dummy for result of cost_sort */
	Path		agg_path;		/* dummy for result of cost_agg */
	MemoryContext oldcontext;
	List	   *sub_targetlist;
	List	   *l;
	int			numCols;

	/* Caller made a mistake if subpath isn't cheapest_total */
	Assert(subpath == rel->cheapest_total_path);

	/* If result already cached, return it */
	if (rel->cheapest_unique_path)
		return (UniquePath *) rel->cheapest_unique_path;

	/*
	 * We must ensure path struct is allocated in same context as parent
	 * rel; otherwise GEQO memory management causes trouble.  (Compare
	 * best_inner_indexscan().)
	 */
	oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel));

	pathnode = makeNode(UniquePath);

	/* There is no substructure to allocate, so can switch back right away */
	MemoryContextSwitchTo(oldcontext);

	pathnode->path.pathtype = T_Unique;
	pathnode->path.parent = rel;

	/*
	 * Treat the output as always unsorted, since we don't necessarily
	 * have pathkeys to represent it.
	 */
	pathnode->path.pathkeys = NIL;

	pathnode->subpath = subpath;

	/*
	 * Try to identify the targetlist that will actually be unique-ified.
	 * In current usage, this routine is only used for sub-selects of IN
	 * clauses, so we should be able to find the tlist in in_info_list.
	 */
	sub_targetlist = NIL;
	foreach(l, root->in_info_list)
	{
		InClauseInfo *ininfo = (InClauseInfo *) lfirst(l);

		if (bms_equal(ininfo->righthand, rel->relids))
		{
			sub_targetlist = ininfo->sub_targetlist;
			break;
		}
	}

	/*
	 * If we know the targetlist, try to estimate number of result rows;
	 * otherwise punt.
	 */
	if (sub_targetlist)
	{
		pathnode->rows = estimate_num_groups(root, sub_targetlist, rel->rows);
		numCols = length(sub_targetlist);
	}
	else
	{
		pathnode->rows = rel->rows;
		numCols = length(FastListValue(&rel->reltargetlist));
	}

	/*
	 * Estimate cost for sort+unique implementation
	 */
	cost_sort(&sort_path, root, NIL,
			  subpath->total_cost,
			  rel->rows,
			  rel->width);

	/*
	 * Charge one cpu_operator_cost per comparison per input tuple. We
	 * assume all columns get compared at most of the tuples.  (XXX
	 * probably this is an overestimate.)  This should agree with
	 * make_unique.
	 */
	sort_path.total_cost += cpu_operator_cost * rel->rows * numCols;

	/*
	 * Is it safe to use a hashed implementation?  If so, estimate and
	 * compare costs.  We only try this if we know the targetlist for sure
	 * (else we can't be sure about the datatypes involved).
	 */
	pathnode->use_hash = false;
	if (enable_hashagg && sub_targetlist && hash_safe_tlist(sub_targetlist))
	{
		/*
		 * Estimate the overhead per hashtable entry at 64 bytes (same as
		 * in planner.c).
		 */
		int			hashentrysize = rel->width + 64;

		if (hashentrysize * pathnode->rows <= SortMem * 1024L)
		{
			cost_agg(&agg_path, root,
					 AGG_HASHED, 0,
					 numCols, pathnode->rows,
					 subpath->startup_cost,
					 subpath->total_cost,
					 rel->rows);
			if (agg_path.total_cost < sort_path.total_cost)
				pathnode->use_hash = true;
		}
	}

	if (pathnode->use_hash)
	{
		pathnode->path.startup_cost = agg_path.startup_cost;
		pathnode->path.total_cost = agg_path.total_cost;
	}
	else
	{
		pathnode->path.startup_cost = sort_path.startup_cost;
		pathnode->path.total_cost = sort_path.total_cost;
	}

	rel->cheapest_unique_path = (Path *) pathnode;

	return pathnode;
}

/*
 * hash_safe_tlist - can datatypes of given tlist be hashed?
 *
 * We assume hashed aggregation will work if the datatype's equality operator
 * is marked hashjoinable.
 *
 * XXX this probably should be somewhere else.	See also hash_safe_grouping
 * in plan/planner.c.
 */
static bool
hash_safe_tlist(List *tlist)
{
	List	   *tl;

	foreach(tl, tlist)
	{
		Node	   *expr = (Node *) lfirst(tl);
		Operator	optup;
		bool		oprcanhash;

		optup = equality_oper(exprType(expr), true);
		if (!optup)
			return false;
		oprcanhash = ((Form_pg_operator) GETSTRUCT(optup))->oprcanhash;
		ReleaseSysCache(optup);
		if (!oprcanhash)
			return false;
	}
	return true;
}

/*
 * create_subqueryscan_path
 *	  Creates a path corresponding to a sequential scan of a subquery,
 *	  returning the pathnode.
 */
Path *
create_subqueryscan_path(RelOptInfo *rel, List *pathkeys)
{
	Path	   *pathnode = makeNode(Path);

	pathnode->pathtype = T_SubqueryScan;
	pathnode->parent = rel;
	pathnode->pathkeys = pathkeys;

	cost_subqueryscan(pathnode, rel);

	return pathnode;
}

/*
 * create_functionscan_path
 *	  Creates a path corresponding to a sequential scan of a function,
 *	  returning the pathnode.
 */
Path *
create_functionscan_path(Query *root, RelOptInfo *rel)
{
	Path	   *pathnode = makeNode(Path);

	pathnode->pathtype = T_FunctionScan;
	pathnode->parent = rel;
	pathnode->pathkeys = NIL;	/* for now, assume unordered result */

	cost_functionscan(pathnode, root, rel);

	return pathnode;
}

/*
 * create_nestloop_path
 *	  Creates a pathnode corresponding to a nestloop join between two
 *	  relations.
 *
 * 'joinrel' is the join relation.
 * 'jointype' is the type of join required
 * 'outer_path' is the outer path
 * 'inner_path' is the inner path
 * 'restrict_clauses' are the RestrictInfo nodes to apply at the join
 * 'pathkeys' are the path keys of the new join path
 *
 * Returns the resulting path node.
 */
NestPath *
create_nestloop_path(Query *root,
					 RelOptInfo *joinrel,
					 JoinType jointype,
					 Path *outer_path,
					 Path *inner_path,
					 List *restrict_clauses,
					 List *pathkeys)
{
	NestPath   *pathnode = makeNode(NestPath);

	pathnode->path.pathtype = T_NestLoop;
	pathnode->path.parent = joinrel;
	pathnode->jointype = jointype;
	pathnode->outerjoinpath = outer_path;
	pathnode->innerjoinpath = inner_path;
	pathnode->joinrestrictinfo = restrict_clauses;
	pathnode->path.pathkeys = pathkeys;

	cost_nestloop(pathnode, root);

	return pathnode;
}

/*
 * create_mergejoin_path
 *	  Creates a pathnode corresponding to a mergejoin join between
 *	  two relations
 *
 * 'joinrel' is the join relation
 * 'jointype' is the type of join required
 * 'outer_path' is the outer path
 * 'inner_path' is the inner path
 * 'restrict_clauses' are the RestrictInfo nodes to apply at the join
 * 'pathkeys' are the path keys of the new join path
 * 'mergeclauses' are the RestrictInfo nodes to use as merge clauses
 *		(this should be a subset of the restrict_clauses list)
 * 'outersortkeys' are the sort varkeys for the outer relation
 * 'innersortkeys' are the sort varkeys for the inner relation
 */
MergePath *
create_mergejoin_path(Query *root,
					  RelOptInfo *joinrel,
					  JoinType jointype,
					  Path *outer_path,
					  Path *inner_path,
					  List *restrict_clauses,
					  List *pathkeys,
					  List *mergeclauses,
					  List *outersortkeys,
					  List *innersortkeys)
{
	MergePath  *pathnode = makeNode(MergePath);

	/*
	 * If the given paths are already well enough ordered, we can skip
	 * doing an explicit sort.
	 */
	if (outersortkeys &&
		pathkeys_contained_in(outersortkeys, outer_path->pathkeys))
		outersortkeys = NIL;
	if (innersortkeys &&
		pathkeys_contained_in(innersortkeys, inner_path->pathkeys))
		innersortkeys = NIL;

	/*
	 * If we are not sorting the inner path, we may need a materialize
	 * node to ensure it can be marked/restored.  (Sort does support
	 * mark/restore, so no materialize is needed in that case.)
	 *
	 * Since the inner side must be ordered, and only Sorts and IndexScans
	 * can create order to begin with, you might think there's no problem
	 * --- but you'd be wrong.  Nestloop and merge joins can *preserve*
	 * the order of their inputs, so they can be selected as the input of
	 * a mergejoin, and they don't support mark/restore at present.
	 */
	if (innersortkeys == NIL &&
		!ExecSupportsMarkRestore(inner_path->pathtype))
		inner_path = (Path *)
			create_material_path(inner_path->parent, inner_path);

	pathnode->jpath.path.pathtype = T_MergeJoin;
	pathnode->jpath.path.parent = joinrel;
	pathnode->jpath.jointype = jointype;
	pathnode->jpath.outerjoinpath = outer_path;
	pathnode->jpath.innerjoinpath = inner_path;
	pathnode->jpath.joinrestrictinfo = restrict_clauses;
	pathnode->jpath.path.pathkeys = pathkeys;
	pathnode->path_mergeclauses = mergeclauses;
	pathnode->outersortkeys = outersortkeys;
	pathnode->innersortkeys = innersortkeys;

	cost_mergejoin(pathnode, root);

	return pathnode;
}

/*
 * create_hashjoin_path
 *	  Creates a pathnode corresponding to a hash join between two relations.
 *
 * 'joinrel' is the join relation
 * 'jointype' is the type of join required
 * 'outer_path' is the cheapest outer path
 * 'inner_path' is the cheapest inner path
 * 'restrict_clauses' are the RestrictInfo nodes to apply at the join
 * 'hashclauses' are the RestrictInfo nodes to use as hash clauses
 *		(this should be a subset of the restrict_clauses list)
 */
HashPath *
create_hashjoin_path(Query *root,
					 RelOptInfo *joinrel,
					 JoinType jointype,
					 Path *outer_path,
					 Path *inner_path,
					 List *restrict_clauses,
					 List *hashclauses)
{
	HashPath   *pathnode = makeNode(HashPath);

	pathnode->jpath.path.pathtype = T_HashJoin;
	pathnode->jpath.path.parent = joinrel;
	pathnode->jpath.jointype = jointype;
	pathnode->jpath.outerjoinpath = outer_path;
	pathnode->jpath.innerjoinpath = inner_path;
	pathnode->jpath.joinrestrictinfo = restrict_clauses;
	/* A hashjoin never has pathkeys, since its ordering is unpredictable */
	pathnode->jpath.path.pathkeys = NIL;
	pathnode->path_hashclauses = hashclauses;

	cost_hashjoin(pathnode, root);

	return pathnode;
}