pathnode.c

关系型数据库 Postgresql 6.5.2

/*-------------------------------------------------------------------------
 *
 * pathnode.c
 *	  Routines to manipulate pathlists and create path nodes
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /usr/local/cvsroot/pgsql/src/backend/optimizer/util/pathnode.c,v 1.42.2.1 1999/08/02 06:27:08 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */
#include <math.h>

#include "postgres.h"

#include "optimizer/cost.h"
#include "optimizer/keys.h"
#include "optimizer/ordering.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/plancat.h"
#include "optimizer/restrictinfo.h"
#include "parser/parsetree.h"

static Path *better_path(Path *new_path, List *unique_paths, bool *is_new);


/*****************************************************************************
 *		MISC. PATH UTILITIES
 *****************************************************************************/

/*
 * path_is_cheaper
 *	  Returns t iff 'path1' is cheaper than 'path2'.
 *
 */
bool
path_is_cheaper(Path *path1, Path *path2)
{
	Cost		cost1 = path1->path_cost;
	Cost		cost2 = path2->path_cost;

	return (bool) (cost1 < cost2);
}

/*
 * set_cheapest
 *	  Finds the minimum cost path from among a relation's paths.
 *
 * 'parent_rel' is the parent relation
 * 'pathlist' is a list of path nodes corresponding to 'parent_rel'
 *
 * Returns and sets the relation entry field with the pathnode that
 * is minimum.
 *
 */
Path *
set_cheapest(RelOptInfo *parent_rel, List *pathlist)
{
	List	   *p;
	Path	   *cheapest_so_far;

	Assert(pathlist != NIL);
	Assert(IsA(parent_rel, RelOptInfo));

	cheapest_so_far = (Path *) lfirst(pathlist);

	foreach(p, lnext(pathlist))
	{
		Path	   *path = (Path *) lfirst(p);

		if (path_is_cheaper(path, cheapest_so_far))
			cheapest_so_far = path;
	}

	parent_rel->cheapestpath = cheapest_so_far;

	return cheapest_so_far;
}

/*
 * add_pathlist
 *	  For each path in the list 'new_paths', add to the list 'unique_paths'
 *	  only those paths that are unique (i.e., unique ordering and ordering
 *	  keys).  Should a conflict arise, the more expensive path is thrown out,
 *	  thereby pruning the plan space.  But we don't prune if xfunc
 *	  told us not to.
 *
 * 'parent_rel' is the relation entry to which these paths correspond.
 *
 * Returns the list of unique pathnodes.
 *
 */
List *
add_pathlist(RelOptInfo *parent_rel, List *unique_paths, List *new_paths)
{
	List	   *p1;

	foreach(p1, new_paths)
	{
		Path	   *new_path = (Path *) lfirst(p1);
		Path	   *old_path;
		bool		is_new;

		/* Is this new path already in unique_paths? */
		if (member(new_path, unique_paths))
			continue;

		/* Find best matching path */
		old_path = better_path(new_path, unique_paths, &is_new);

		if (is_new)
		{
			/* This is a brand new path.  */
			new_path->parent = parent_rel;
			unique_paths = lcons(new_path, unique_paths);
		}
		else if (old_path == NULL)
		{
			;					/* do nothing if path is not cheaper */
		}
		else if (old_path != NULL)
		{						/* (IsA(old_path,Path)) { */
			new_path->parent = parent_rel;
			if (!parent_rel->pruneable)
				unique_paths = lcons(new_path, unique_paths);
			else
				unique_paths = lcons(new_path,
									 LispRemove(old_path, unique_paths));
		}
	}
	return unique_paths;
}

/*
 * better_path
 *	  Determines whether 'new_path' has the same ordering and keys as some
 *	  path in the list 'unique_paths'.	If there is a redundant path,
 *	  eliminate the more expensive path.
 *
 * Returns:
 *	  The old path - if 'new_path' matches some path in 'unique_paths' and is
 *				cheaper
 *	  nil - if 'new_path' matches but isn't cheaper
 *	  t - if there is no path in the list with the same ordering and keys
 *
 */
static Path *
better_path(Path *new_path, List *unique_paths, bool *is_new)
{
	Path	   *path = (Path *) NULL;
	List	   *temp = NIL;
	int			better_key;
	int			better_sort;

#ifdef OPTDUP_DEBUG
	printf("better_path entry\n");
	printf("new\n");
	pprint(new_path);
	printf("unique_paths\n");
	pprint(unique_paths);
#endif

	foreach(temp, unique_paths)
	{
		path = (Path *) lfirst(temp);

#ifdef OPTDUP_DEBUG
		if (!pathkeys_match(new_path->pathkeys, path->pathkeys, &better_key) ||
			better_key != 0)
		{
			printf("betterkey = %d\n", better_key);
			printf("newpath\n");
			pprint(new_path->pathkeys);
			printf("oldpath\n");
			pprint(path->pathkeys);
			if (path->pathkeys && new_path->pathkeys &&
				length(lfirst(path->pathkeys)) >= 2		/* &&
														 * length(lfirst(path->pa
														 * thkeys)) <
														 * length(lfirst(new_path
					->pathkeys)) */ )
				sleep(0);		/* set breakpoint here */
		}
		if (!pathorder_match(new_path->pathorder, path->pathorder,
							 &better_sort) ||
			better_sort != 0)
		{
			printf("neword\n");
			pprint(new_path->pathorder);
			printf("oldord\n");
			pprint(path->pathorder);
		}
#endif

		if (pathkeys_match(new_path->pathkeys, path->pathkeys,
						   &better_key) &&
			pathorder_match(new_path->pathorder, path->pathorder,
							&better_sort))
		{

			/*
			 * Replace pathkeys that match exactly, {{1,2}}, {{1,2}}
			 * Replace pathkeys {{1,2}} with {{1,2,3}}} if the latter is
			 * not more expensive and replace unordered path with ordered
			 * path if it is not more expensive.  Favor sorted keys over
			 * unsorted keys in the same way.
			 */
			/* same keys, and new is cheaper, use it */
			if ((better_key == 0 && better_sort == 0 &&
				 new_path->path_cost < path->path_cost) ||

			/* new is better, and cheaper, use it */
				(((better_key == 1 && better_sort != 2) ||
				  (better_key != 2 && better_sort == 1)) &&
				 new_path->path_cost <= path->path_cost))
			{
#ifdef OPTDUP_DEBUG
				printf("replace with new %p old %p better key %d better sort %d\n", &new_path, &path, better_key, better_sort);
				printf("new\n");
				pprint(new_path);
				printf("old\n");
				pprint(path);
#endif
				*is_new = false;
				return path;
			}

			/* same keys, new is more expensive, stop */
			if ((better_key == 0 && better_sort == 0 &&
				 new_path->path_cost >= path->path_cost) ||

			/* old is better, and less expensive, stop */
				(((better_key == 2 && better_sort != 1) ||
				  (better_key != 1 && better_sort == 2)) &&
				 new_path->path_cost >= path->path_cost))
			{
#ifdef OPTDUP_DEBUG
				printf("skip new %p old %p better key %d better sort %d\n", &new_path, &path, better_key, better_sort);
				printf("new\n");
				pprint(new_path);
				printf("old\n");
				pprint(path);
#endif
				*is_new = false;
				return NULL;
			}
		}
	}

#ifdef OPTDUP_DEBUG
	printf("add new %p old %p better key %d better sort %d\n", &new_path, &path, better_key, better_sort);
	printf("new\n");
	pprint(new_path);
#endif

	*is_new = true;
	return NULL;
}



/*****************************************************************************
 *		PATH NODE CREATION ROUTINES
 *****************************************************************************/

/*
 * create_seqscan_path
 *	  Creates a path corresponding to a sequential scan, returning the
 *	  pathnode.
 *
 */
Path *
create_seqscan_path(RelOptInfo *rel)
{
	int			relid = 0;

	Path	   *pathnode = makeNode(Path);

	pathnode->pathtype = T_SeqScan;
	pathnode->parent = rel;
	pathnode->path_cost = 0.0;
	pathnode->pathorder = makeNode(PathOrder);
	pathnode->pathorder->ordtype = SORTOP_ORDER;
	pathnode->pathorder->ord.sortop = NULL;
	pathnode->pathkeys = NIL;

	/*
	 * copy restrictinfo list into path for expensive function processing
	 * JMH, 7/7/92
	 */
	pathnode->loc_restrictinfo = (List *) copyObject((Node *) rel->restrictinfo);

	if (rel->relids != NULL)
		relid = lfirsti(rel->relids);

	pathnode->path_cost = cost_seqscan(relid,
									   rel->pages, rel->tuples);
	/* add in expensive functions cost!  -- JMH, 7/7/92 */
#ifdef NOT_USED
	if (XfuncMode != XFUNC_OFF)
		pathnode->path_cost += xfunc_get_path_cost(pathnode);
#endif
	return pathnode;
}

/*
 * create_index_path
 *	  Creates a single path node for an index scan.
 *
 * 'rel' is the parent rel
 * 'index' is the pathnode for the index on 'rel'
 * 'restriction_clauses' is a list of restriction clause nodes.
 * 'is_join_scan' is a flag indicating whether or not the index is being
 *		considered because of its sort order.
 *
 * Returns the new path node.
 *
 */
IndexPath  *
create_index_path(Query *root,