geo_selfuncs.c

来自「postgresql8.3.4源码,开源数据库」· C语言 代码 · 共 96 行

/*-------------------------------------------------------------------------
 *
 * geo_selfuncs.c
 *	  Selectivity routines registered in the operator catalog in the
 *	  "oprrest" and "oprjoin" attributes.
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/utils/adt/geo_selfuncs.c,v 1.31 2008/01/01 19:45:52 momjian Exp $
 *
 *	XXX These are totally bogus.  Perhaps someone will make them do
 *	something reasonable, someday.
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "utils/geo_decls.h"


/*
 *	Selectivity functions for geometric operators.	These are bogus -- unless
 *	we know the actual key distribution in the index, we can't make a good
 *	prediction of the selectivity of these operators.
 *
 *	Note: the values used here may look unreasonably small.  Perhaps they
 *	are.  For now, we want to make sure that the optimizer will make use
 *	of a geometric index if one is available, so the selectivity had better
 *	be fairly small.
 *
 *	In general, GiST needs to search multiple subtrees in order to guarantee
 *	that all occurrences of the same key have been found.  Because of this,
 *	the estimated cost for scanning the index ought to be higher than the
 *	output selectivity would indicate.	gistcostestimate(), over in selfuncs.c,
 *	ought to be adjusted accordingly --- but until we can generate somewhat
 *	realistic numbers here, it hardly matters...
 */


/*
 * Selectivity for operators that depend on area, such as "overlap".
 */

Datum
areasel(PG_FUNCTION_ARGS)
{
	PG_RETURN_FLOAT8(0.005);
}

Datum
areajoinsel(PG_FUNCTION_ARGS)
{
	PG_RETURN_FLOAT8(0.005);
}

/*
 *	positionsel
 *
 * How likely is a box to be strictly left of (right of, above, below)
 * a given box?
 */

Datum
positionsel(PG_FUNCTION_ARGS)
{
	PG_RETURN_FLOAT8(0.1);
}

Datum
positionjoinsel(PG_FUNCTION_ARGS)
{
	PG_RETURN_FLOAT8(0.1);
}

/*
 *	contsel -- How likely is a box to contain (be contained by) a given box?
 *
 * This is a tighter constraint than "overlap", so produce a smaller
 * estimate than areasel does.
 */

Datum
contsel(PG_FUNCTION_ARGS)
{
	PG_RETURN_FLOAT8(0.001);
}

Datum
contjoinsel(PG_FUNCTION_ARGS)
{
	PG_RETURN_FLOAT8(0.001);
}