PostgreSQL/src/backend/optimizer/path/allpaths.c

/*-------------------------------------------------------------------------
 *
 * allpaths.c
 *	  Routines to find possible search paths for processing a query
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/allpaths.c,v 1.56 2000/01/22 23:50:14 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "optimizer/cost.h"
#include "optimizer/geqo.h"
#include "optimizer/internal.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"

#ifdef GEQO
bool		enable_geqo = true;
#else
bool		enable_geqo = false;
#endif

int			geqo_rels = GEQO_RELS;


static void set_base_rel_pathlist(Query *root, List *rels);
static RelOptInfo *make_one_rel_by_joins(Query *root, List *rels,
					  int levels_needed);

#ifdef OPTIMIZER_DEBUG
static void debug_print_rel(Query *root, RelOptInfo *rel);

#endif

/*
 * make_one_rel
 *	  Finds all possible access paths for executing a query, returning a
 *	  single rel.
 *
 * 'rels' is the list of single relation entries appearing in the query
 */
RelOptInfo *
make_one_rel(Query *root, List *rels)
{
	int			levels_needed;

	/*
	 * Set the number of join (not nesting) levels yet to be processed.
	 */
	levels_needed = length(rels);

	if (levels_needed <= 0)
		return NULL;

	/*
	 * Generate access paths for the base rels.
	 */
	set_base_rel_pathlist(root, rels);

	if (levels_needed <= 1)
	{
		/*
		 * Single relation, no more processing is required.
		 */
		return lfirst(rels);
	}
	else
	{
		/*
		 * Generate join tree.
		 */
		return make_one_rel_by_joins(root, rels, levels_needed);
	}
}

/*
 * set_base_rel_pathlist
 *	  Finds all paths available for scanning each relation entry in
 *	  'rels'.  Sequential scan and any available indices are considered
 *	  if possible (indices are not considered for lower nesting levels).
 *	  All useful paths are attached to the relation's 'pathlist' field.
 *
 *	  MODIFIES: rels
 */
static void
set_base_rel_pathlist(Query *root, List *rels)
{
	List	   *temp;

	foreach(temp, rels)
	{
		RelOptInfo *rel = (RelOptInfo *) lfirst(temp);
		List	   *indices = find_relation_indices(root, rel);
		List	   *sequential_scan_list;
		List	   *rel_index_scan_list;
		List	   *or_index_scan_list;
		List	   *tidscan_pathlist;

		sequential_scan_list = lcons(create_seqscan_path(rel), NIL);
		/* Tid Scan Pathlist add */
		tidscan_pathlist = create_tidscan_paths(root, rel);
		if (tidscan_pathlist)
			sequential_scan_list = nconc(sequential_scan_list,
										 tidscan_pathlist);
		rel_index_scan_list = create_index_paths(root,
												 rel,
												 indices,
												 rel->restrictinfo,
												 rel->joininfo);

		/* Note: create_or_index_paths depends on create_index_paths
		 * to have marked OR restriction clauses with relevant indices;
		 * this is why it doesn't need to be given the full list of indices.
		 */
		or_index_scan_list = create_or_index_paths(root, rel,
												   rel->restrictinfo);

		/* add_pathlist will discard any paths that are dominated by
		 * another available path, keeping only those paths that are
		 * superior along at least one dimension of cost or sortedness.
		 */
		rel->pathlist = add_pathlist(rel,
									 sequential_scan_list,
									 nconc(rel_index_scan_list,
										   or_index_scan_list));

		/* Now find the cheapest of the paths */
		set_cheapest(rel, rel->pathlist);
		/* Mark rel with estimated output rows and width */
		set_rel_rows_width(root, rel);
	}
}

/*
 * make_one_rel_by_joins
 *	  Find all possible joinpaths for a query by successively finding ways
 *	  to join single relations into join relations.
 *
 *	  Find all possible joinpaths(bushy trees) for a query by systematically
 *	  finding ways to join relations(both original and derived) together.
 *
 * 'rels' is the current list of relations for which join paths
 *				are to be found, i.e., the current list of relations that
 *				have already been derived.
 * 'levels_needed' is the number of iterations needed
 *
 * Returns the final level of join relations, i.e., the relation that is
 * the result of joining all the original relations together.
 */
static RelOptInfo *
make_one_rel_by_joins(Query *root, List *rels, int levels_needed)
{
	List	   *x;
	List	   *joined_rels = NIL;
	RelOptInfo *rel;

	/*******************************************
	 * genetic query optimizer entry point	   *
	 *	  <utesch@aut.tu-freiberg.de>		   *
	 *******************************************/
	if (enable_geqo && length(root->base_rel_list) >= geqo_rels)
		return geqo(root);

	/*******************************************
	 * rest will be skipped in case of GEQO    *
	 *******************************************/

	while (--levels_needed)
	{

		/*
		 * Determine all possible pairs of relations to be joined at this
		 * level.  Determine paths for joining these relation pairs and
		 * modify 'joined_rels' accordingly, then eliminate redundant join
		 * relations.
		 */
		joined_rels = make_rels_by_joins(root, rels);

		update_rels_pathlist_for_joins(root, joined_rels);

		merge_rels_with_same_relids(joined_rels);

		root->join_rel_list = rels = joined_rels;

#ifdef NOT_USED

		/*
		 * * for each expensive predicate in each path in each distinct
		 * rel, * consider doing pullup  -- JMH
		 */
		if (XfuncMode != XFUNC_NOPULL && XfuncMode != XFUNC_OFF)
			foreach(x, joined_rels)
				xfunc_trypullup((RelOptInfo *) lfirst(x));
#endif

		rels_set_cheapest(root, joined_rels);

		foreach(x, joined_rels)
		{
			rel = (RelOptInfo *) lfirst(x);

#ifdef OPTIMIZER_DEBUG
			printf("levels left: %d\n", levels_needed);
			debug_print_rel(root, rel);
#endif
		}

	}

	return get_cheapest_complete_rel(rels);
}

/*****************************************************************************
 *
 *****************************************************************************/

#ifdef OPTIMIZER_DEBUG
static void
print_joinclauses(Query *root, List *clauses)
{
	List	   *l;
	extern void print_expr(Node *expr, List *rtable);	/* in print.c */

	foreach(l, clauses)
	{
		RestrictInfo *c = lfirst(l);

		print_expr((Node *) c->clause, root->rtable);
		if (lnext(l))
			printf(" ");
	}
}

static void
print_path(Query *root, Path *path, int indent)
{
	char	   *ptype = NULL;
	JoinPath   *jp;
	bool		join = false;
	int			i;

	for (i = 0; i < indent; i++)
		printf("\t");

	switch (nodeTag(path))
	{
		case T_Path:
			ptype = "SeqScan";
			join = false;
			break;
		case T_IndexPath:
			ptype = "IdxScan";
			join = false;
			break;
		case T_NestPath:
			ptype = "Nestloop";
			join = true;
			break;
		case T_MergePath:
			ptype = "MergeJoin";
			join = true;
			break;
		case T_HashPath:
			ptype = "HashJoin";
			join = true;
			break;
		default:
			break;
	}
	if (join)
	{
		jp = (JoinPath *) path;
		printf("%s rows=%.0f cost=%f\n",
			   ptype, path->parent->rows, path->path_cost);
		switch (nodeTag(path))
		{
			case T_MergePath:
			case T_HashPath:
				for (i = 0; i < indent + 1; i++)
					printf("\t");
				printf("   clauses=(");
				print_joinclauses(root, jp->path.parent->restrictinfo);
				printf(")\n");

				if (nodeTag(path) == T_MergePath)
				{
					MergePath  *mp = (MergePath *) path;

					if (mp->outersortkeys || mp->innersortkeys)
					{
						for (i = 0; i < indent + 1; i++)
							printf("\t");
						printf("   sortouter=%d sortinner=%d\n",
							   ((mp->outersortkeys) ? 1 : 0),
							   ((mp->innersortkeys) ? 1 : 0));
					}
				}
				break;
			default:
				break;
		}
		print_path(root, jp->outerjoinpath, indent + 1);
		print_path(root, jp->innerjoinpath, indent + 1);
	}
	else
	{
		int			relid = lfirsti(path->parent->relids);

		printf("%s(%d) rows=%.0f cost=%f\n",
			   ptype, relid, path->parent->rows, path->path_cost);

		if (IsA(path, IndexPath))
		{
			printf("  pathkeys=");
			print_pathkeys(path->pathkeys, root->rtable);
		}
	}
}

static void
debug_print_rel(Query *root, RelOptInfo *rel)
{
	List	   *l;

	printf("(");
	foreach(l, rel->relids)
		printf("%d ", lfirsti(l));
	printf("): rows=%.0f width=%d\n", rel->rows, rel->width);

	printf("\tpath list:\n");
	foreach(l, rel->pathlist)
		print_path(root, lfirst(l), 1);
	printf("\tcheapest path:\n");
	print_path(root, rel->cheapestpath, 1);
}

#endif	 /* OPTIMIZER_DEBUG */