clausesel.c

关系型数据库 Postgresql 6.5.2

/*-------------------------------------------------------------------------
 *
 * clausesel.c
 *	  Routines to compute and set clause selectivities
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /usr/local/cvsroot/pgsql/src/backend/optimizer/path/clausesel.c,v 1.20.2.1 1999/08/02 06:26:57 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_operator.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/internal.h"
#include "optimizer/plancat.h" 
#include "optimizer/restrictinfo.h"
#include "parser/parsetree.h" 
#include "utils/lsyscache.h"

static Cost compute_selec(Query *root, List *clauses, List *or_selectivities);

/****************************************************************************
 *		ROUTINES TO SET CLAUSE SELECTIVITIES
 ****************************************************************************/

/*
 * set_clause_selectivities -
 *	  Sets the selectivity field for each of clause in 'restrictinfo-list'
 *	  to 'new-selectivity'.  If the selectivity has already been set, reset
 *	  it only if the new one is better.
 *
 * Returns nothing of interest.
 *
 */
void
set_clause_selectivities(List *restrictinfo_list, Cost new_selectivity)
{
	List	   *temp;
	RestrictInfo *clausenode;
	Cost		cost_clause;

	foreach(temp, restrictinfo_list)
	{
		clausenode = (RestrictInfo *) lfirst(temp);
		cost_clause = clausenode->selectivity;
		if (cost_clause <= 0 || new_selectivity < cost_clause)
			clausenode->selectivity = new_selectivity;
	}
}

/*
 * product_selec -
 *	  Multiplies the selectivities of each clause in 'restrictinfo-list'.
 *
 * Returns a flonum corresponding to the selectivity of 'restrictinfo-list'.
 */
Cost
product_selec(List *restrictinfo_list)
{
	Cost		result = 1.0;

	if (restrictinfo_list != NIL)
	{
		List	   *xclausenode = NIL;
		Cost		temp;

		foreach(xclausenode, restrictinfo_list)
		{
			temp = ((RestrictInfo *) lfirst(xclausenode))->selectivity;
			result = result * temp;
		}
	}
	return result;
}

/*
 * set_rest_relselec -
 *	  Scans through clauses on each relation and assigns a selectivity to
 *	  those clauses that haven't been assigned a selectivity by an index.
 *
 * Returns nothing of interest.
 * MODIFIES: selectivities of the various rel's restrictinfo
 *		  slots.
 */
void
set_rest_relselec(Query *root, List *rel_list)
{
	RelOptInfo *rel;
	List	   *x;

	foreach(x, rel_list)
	{
		rel = (RelOptInfo *) lfirst(x);
		set_rest_selec(root, rel->restrictinfo);
	}
}

/*
 * set_rest_selec -
 *	  Sets the selectivity fields for those clauses within a single
 *	  relation's 'restrictinfo-list' that haven't already been set.
 *
 * Returns nothing of interest.
 *
 */
void
set_rest_selec(Query *root, List *restrictinfo_list)
{
	List	   *temp = NIL;
	RestrictInfo *clausenode = (RestrictInfo *) NULL;
	Cost		cost_clause;

	foreach(temp, restrictinfo_list)
	{
		clausenode = (RestrictInfo *) lfirst(temp);
		cost_clause = clausenode->selectivity;

		/*
		 * Check to see if the selectivity of this clause or any 'or'
		 * subclauses (if any) haven't been set yet.
		 */
		if (cost_clause <= 0 || valid_or_clause(clausenode))
		{
			clausenode->selectivity = compute_clause_selec(root,
											 (Node *) clausenode->clause,
									 lcons(makeFloat(cost_clause), NIL));
		}
	}
}

/****************************************************************************
 *		ROUTINES TO COMPUTE SELECTIVITIES
 ****************************************************************************/

/*
 * compute_clause_selec -
 *	  Given a clause, this routine will compute the selectivity of the
 *	  clause by calling 'compute_selec' with the appropriate parameters
 *	  and possibly use that return value to compute the real selectivity
 *	  of a clause.
 *
 * 'or-selectivities' are selectivities that have already been assigned
 *		to subclauses of an 'or' clause.
 *
 * Returns a flonum corresponding to the clause selectivity.
 *
 */
Cost
compute_clause_selec(Query *root, Node *clause, List *or_selectivities)
{
	if (is_opclause(clause))
		return compute_selec(root, lcons(clause, NIL), or_selectivities);
	else if (not_clause(clause))
	{

		/*
		 * 'not' gets "1.0 - selectivity-of-inner-clause".
		 */
		return (1.000000 - compute_selec(root,
								 lcons(get_notclausearg((Expr *) clause),
									   NIL),
										 or_selectivities));
	}
	else if (or_clause(clause))
	{

		/*
		 * Both 'or' and 'and' clauses are evaluated as described in
		 * (compute_selec).
		 */
		return compute_selec(root, ((Expr *) clause)->args, or_selectivities);
	}
	else
		return compute_selec(root, lcons(clause, NIL), or_selectivities);
}

/*
 * compute_selec -
 *	  Computes the selectivity of a clause.
 *
 *	  If there is more than one clause in the argument 'clauses', then the
 *	  desired selectivity is that of an 'or' clause.  Selectivities for an
 *	  'or' clause such as (OR a b) are computed by finding the selectivity
 *	  of a (s1) and b (s2) and computing s1+s2 - s1*s2.
 *
 *	  In addition, if the clause is an 'or' clause, individual selectivities
 *	  may have already been assigned by indices to subclauses.	These values
 *	  are contained in the list 'or-selectivities'.
 *
 * Returns the clause selectivity as a flonum.
 *
 */
static Cost
compute_selec(Query *root, List *clauses, List *or_selectivities)
{
	Cost		s1 = 0;
	List	   *clause = lfirst(clauses);

	if (clause == NULL)
		s1 = 1.0;
	else if (IsA(clause, Param))
	{
		/* XXX How're we handling this before?? -ay */
		s1 = 1.0;
	}
	else if (IsA(clause, Const))
		s1 = ((bool) ((Const *) clause)->constvalue) ? 1.0 : 0.0;
	else if (IsA(clause, Var))
	{
		Oid			relid = getrelid(((Var *) clause)->varno,
									 root->rtable);

		/*
		 * we have a bool Var.	This is exactly equivalent to the clause:
		 * reln.attribute = 't' so we compute the selectivity as if that
		 * is what we have. The magic #define constants are a hack.  I
		 * didn't want to have to do system cache look ups to find out all
		 * of that info.
		 */

		s1 = restriction_selectivity(F_EQSEL,
									 BooleanEqualOperator,
									 relid,
									 ((Var *) clause)->varoattno,
									 "t",
									 _SELEC_CONSTANT_RIGHT_);
	}
	else if (or_selectivities)
	{
		/* If s1 has already been assigned by an index, use that value. */
		List	   *this_sel = lfirst(or_selectivities);

		s1 = floatVal(this_sel);
	}
	else if (is_funcclause((Node *) clause))
	{
		/* this isn't an Oper, it's a Func!! */

		/*
		 * This is not an operator, so we guess at the selectivity. THIS
		 * IS A HACK TO GET V4 OUT THE DOOR.  FUNCS SHOULD BE ABLE TO HAVE
		 * SELECTIVITIES THEMSELVES.	   -- JMH 7/9/92
		 */
		s1 = 0.1;
	}
	else if (not_clause((Node *) clause))
	{
		/* negate this baby */
		return 1 - compute_selec(root, ((Expr *) clause)->args, or_selectivities);
	}
	else if (is_subplan((Node *) clause))
	{

		/*
		 * Just for the moment! FIX ME! - vadim 02/04/98
		 */
		s1 = 1.0;
	}
	else if (NumRelids((Node *) clause) == 1)
	{

		/*
		 * ...otherwise, calculate s1 from 'clauses'. The clause is not a
		 * join clause, since there is only one relid in the clause.  The
		 * clause selectivity will be based on the operator selectivity
		 * and operand values.
		 */
		Oid			opno = ((Oper *) ((Expr *) clause)->oper)->opno;
		RegProcedure oprrest = get_oprrest(opno);
		Oid			relid;
		int			relidx;
		AttrNumber	attno;
		Datum		constval;
		int			flag;

		get_relattval((Node *) clause, &relidx, &attno, &constval, &flag);
		relid = getrelid(relidx, root->rtable);

		/*
		 * if the oprrest procedure is missing for whatever reason, use a
		 * selectivity of 0.5
		 */
		if (!oprrest)
			s1 = (Cost) (0.5);
		else if (attno == InvalidAttrNumber)
		{

			/*
			 * attno can be Invalid if the clause had a function in it,
			 * i.e.   WHERE myFunc(f) = 10
			 */
			/* this should be FIXED somehow to use function selectivity */
			s1 = (Cost) (0.5);
		}
		else
			s1 = (Cost) restriction_selectivity(oprrest,
												opno,
												relid,
												attno,
												(char *) constval,
												flag);

	}
	else
	{

		/*
		 * The clause must be a join clause.  The clause selectivity will
		 * be based on the relations to be scanned and the attributes they
		 * are to be joined on.
		 */
		Oid			opno = ((Oper *) ((Expr *) clause)->oper)->opno;
		RegProcedure oprjoin = get_oprjoin(opno);
		int			relid1,
					relid2;
		AttrNumber	attno1,
					attno2;

		get_rels_atts((Node *) clause, &relid1, &attno1, &relid2, &attno2);
		relid1 = getrelid(relid1, root->rtable);
		relid2 = getrelid(relid2, root->rtable);

		/*
		 * if the oprjoin procedure is missing for whatever reason, use a
		 * selectivity of 0.5
		 */
		if (!oprjoin)
			s1 = (Cost) (0.5);
		else
			s1 = (Cost) join_selectivity(oprjoin,
										 opno,
										 relid1,
										 attno1,
										 relid2,
										 attno2);
	}

	/*
	 * A null clause list eliminates no tuples, so return a selectivity of
	 * 1.0.  If there is only one clause, the selectivity is not that of
	 * an 'or' clause, but rather that of the single clause.
	 */

	if (lnext(clauses) == NIL)
		return s1;
	else
	{
		/* Compute selectivity of the 'or'ed subclauses. */
		/* Added check for taking lnext(NIL).  -- JMH 3/9/92 */
		Cost		s2;

		if (or_selectivities != NIL)
			s2 = compute_selec(root, lnext(clauses), lnext(or_selectivities));
		else
			s2 = compute_selec(root, lnext(clauses), NIL);
		return s1 + s2 - s1 * s2;
	}
}