postgresql/src/backend/optimizer/path/costsize.c

/*-------------------------------------------------------------------------
 *
 * costsize.c--
 *    Routines to compute (and set) relation sizes and path costs
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.3 1996/07/22 23:30:50 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */
#include <math.h>
#ifdef WIN32
#include <float.h>
#include <limits.h>
#define MAXINT        INT_MAX
#else
# if defined(PORTNAME_BSD44_derived) || \
     defined(PORTNAME_bsdi) || \
     defined(PORTNAME_bsdi_2_1)
# include <machine/limits.h>
# define MAXINT	INT_MAX
# else
# include <values.h>
# endif /* !PORTNAME_BSD44_derived */
#endif /* WIN32 */

#include "postgres.h"

#include "nodes/relation.h"

#include "optimizer/cost.h"
#include "optimizer/internal.h"
#include "optimizer/keys.h"
#include "optimizer/tlist.h"

#include "storage/bufmgr.h"	/* for BLCKSZ */

static int compute_attribute_width(TargetEntry *tlistentry);
static double base_log(double x, double b);

int _disable_cost_ = 30000000;
 
bool _enable_seqscan_ =     true;
bool _enable_indexscan_ =   true;
bool _enable_sort_ =        true;
bool _enable_hash_ =        true;
bool _enable_nestloop_ =    true;
bool _enable_mergesort_ =   true;
bool _enable_hashjoin_ =    true;

/*    
 * cost_seqscan--
 *    Determines and returns the cost of scanning a relation sequentially.
 *    If the relation is a temporary to be materialized from a query
 *    embedded within a data field (determined by 'relid' containing an
 *    attribute reference), then a predetermined constant is returned (we
 *    have NO IDEA how big the result of a POSTQUEL procedure is going to
 *    be).
 *    
 *    	disk = p
 *    	cpu = *CPU-PAGE-WEIGHT* * t
 *    
 * 'relid' is the relid of the relation to be scanned
 * 'relpages' is the number of pages in the relation to be scanned
 *  	(as determined from the system catalogs)
 * 'reltuples' is the number of tuples in the relation to be scanned
 *    
 * Returns a flonum.
 *    
 */
Cost
cost_seqscan(int relid, int relpages, int reltuples)
{
    Cost temp = 0;

    if ( !_enable_seqscan_ )
	temp += _disable_cost_;

    if (relid < 0) {
	/*
	 * cost of sequentially scanning a materialized temporary relation
	 */
	temp += _TEMP_SCAN_COST_;
    } else {
	temp += relpages;
	temp += _CPU_PAGE_WEIGHT_ * reltuples;
    }
    Assert(temp >= 0);
    return(temp);
}


/*    
 * cost_index--
 *    Determines and returns the cost of scanning a relation using an index.
 *    
 *    	disk = expected-index-pages + expected-data-pages
 *    	cpu = *CPU-PAGE-WEIGHT* *
 *    		(expected-index-tuples + expected-data-tuples)
 *    
 * 'indexid' is the index OID
 * 'expected-indexpages' is the number of index pages examined in the scan
 * 'selec' is the selectivity of the index
 * 'relpages' is the number of pages in the main relation
 * 'reltuples' is the number of tuples in the main relation
 * 'indexpages' is the number of pages in the index relation
 * 'indextuples' is the number of tuples in the index relation
 *    
 * Returns a flonum.
 *    
 */
Cost
cost_index(Oid indexid,
	   int expected_indexpages,
	   Cost selec,
	   int relpages,
	   int reltuples,
	   int indexpages,
	   int indextuples,
	   bool is_injoin)
{
    Cost temp;
    Cost temp2;

    temp = temp2 = (Cost) 0;

    if (!_enable_indexscan_ && !is_injoin)
	temp += _disable_cost_;

    /* expected index relation pages */
    temp += expected_indexpages;

    /*   about one base relation page */
    temp += Min(relpages,(int)ceil((double)selec*indextuples));

    /*
     * per index tuple
     */
    temp2 += selec * indextuples;
    temp2 += selec * reltuples;

    temp =  temp + (_CPU_PAGE_WEIGHT_ * temp2);
    Assert(temp >= 0);
    return(temp);
}

/*    
 * cost_sort--
 *    Determines and returns the cost of sorting a relation by considering
 *    1. the cost of doing an external sort:	XXX this is probably too low
 *    		disk = (p lg p)
 *    		cpu = *CPU-PAGE-WEIGHT* * (t lg t)
 *    2. the cost of reading the sort result into memory (another seqscan)
 *       unless 'noread' is set
 *    
 * 'keys' is a list of sort keys
 * 'tuples' is the number of tuples in the relation
 * 'width' is the average tuple width in bytes
 * 'noread' is a flag indicating that the sort result can remain on disk
 * 		(i.e., the sort result is the result relation)
 *    
 * Returns a flonum.
 *    
 */
Cost
cost_sort(List *keys, int tuples, int width, bool noread)
{
    Cost temp = 0;
    int npages = page_size (tuples,width);
    Cost pages = (Cost)npages;
    Cost numTuples = tuples;
    
    if ( !_enable_sort_ ) 
	temp += _disable_cost_ ;
    if (tuples == 0 || keys==NULL)
	{
	    Assert(temp >= 0);
	    return(temp);
	}
    temp += pages * base_log((double)pages, (double)2.0);

    /*
     * could be base_log(pages, NBuffers), but we are only doing 2-way merges
     */
    temp += _CPU_PAGE_WEIGHT_ *
	numTuples * base_log((double)pages,(double)2.0);

    if( !noread )
	temp = temp + cost_seqscan(_TEMP_RELATION_ID_, npages, tuples);
    Assert(temp >= 0);

    return(temp);
}


/*    
 * cost_result--
 *    Determines and returns the cost of writing a relation of 'tuples'
 *    tuples of 'width' bytes out to a result relation.
 *    
 * Returns a flonum.
 *
 */
Cost
cost_result(int tuples, int width)
{
    Cost temp =0;
    temp = temp + page_size(tuples,width);
    temp = temp + _CPU_PAGE_WEIGHT_ * tuples;
    Assert(temp >= 0);
    return(temp);
}

/*    
 * cost_nestloop--
 *    Determines and returns the cost of joining two relations using the 
 *    nested loop algorithm.
 *    
 * 'outercost' is the (disk+cpu) cost of scanning the outer relation
 * 'innercost' is the (disk+cpu) cost of scanning the inner relation
 * 'outertuples' is the number of tuples in the outer relation
 *    
 * Returns a flonum.
 *
 */
Cost
cost_nestloop(Cost outercost,
	      Cost innercost,
	      int outertuples,
	      int innertuples,
	      int outerpages,
	      bool is_indexjoin)
{
    Cost temp =0;

    if ( !_enable_nestloop_ ) 
	temp += _disable_cost_;
    temp += outercost;
    temp += outertuples * innercost;
    Assert(temp >= 0);

    return(temp);
}

/*    
 * cost_mergesort--
 *    'outercost' and 'innercost' are the (disk+cpu) costs of scanning the
 *    		outer and inner relations
 *    'outersortkeys' and 'innersortkeys' are lists of the keys to be used
 *    		to sort the outer and inner relations
 *    'outertuples' and 'innertuples' are the number of tuples in the outer
 *    		and inner relations
 *    'outerwidth' and 'innerwidth' are the (typical) widths (in bytes)
 *    		of the tuples of the outer and inner relations
 *    
 * Returns a flonum.
 *    
 */
Cost
cost_mergesort(Cost outercost,
	       Cost innercost,
	       List *outersortkeys,
	       List *innersortkeys,
	       int outersize,
	       int innersize,
	       int outerwidth,
	       int innerwidth)
{
    Cost temp = 0;

    if ( !_enable_mergesort_ ) 
	temp += _disable_cost_;
	
    temp += outercost;
    temp += innercost;
    temp += cost_sort(outersortkeys,outersize,outerwidth,false);
    temp += cost_sort(innersortkeys,innersize,innerwidth,false);
    temp += _CPU_PAGE_WEIGHT_ * (outersize + innersize);
    Assert(temp >= 0);

    return(temp);
}

/*    
 * cost_hashjoin--		XXX HASH
 *    'outercost' and 'innercost' are the (disk+cpu) costs of scanning the
 *    		outer and inner relations
 *    'outerkeys' and 'innerkeys' are lists of the keys to be used
 *    		to hash the outer and inner relations
 *    'outersize' and 'innersize' are the number of tuples in the outer
 *    		and inner relations
 *    'outerwidth' and 'innerwidth' are the (typical) widths (in bytes)
 *    		of the tuples of the outer and inner relations
 *    
 * Returns a flonum.
 */
Cost
cost_hashjoin(Cost outercost,
	      Cost innercost,
	      List *outerkeys,
	      List *innerkeys,
	      int outersize,
	      int innersize,
	      int outerwidth,
	      int innerwidth)
{
    Cost temp = 0;
    int outerpages = page_size (outersize,outerwidth);
    int innerpages = page_size (innersize,innerwidth);
    int nrun = ceil((double)outerpages/(double)NBuffers);

    if (outerpages < innerpages)
	return _disable_cost_;
    if ( !_enable_hashjoin_ ) 
	temp += _disable_cost_;
/*    temp += outercost + (nrun + 1) * innercost; */
    /* 
       the innercost shouldn't be used it.  Instead the 
       cost of hashing the innerpath should be used
       
       ASSUME innercost is 1 for now -- a horrible hack 
                                  - jolly
    */
    temp += outercost + (nrun + 1);

    temp += _CPU_PAGE_WEIGHT_ * (outersize + nrun * innersize);
    Assert(temp >= 0);

    return(temp);
}

/*    
 * compute-rel-size--
 *    Computes the size of each relation in 'rel-list' (after applying 
 *    restrictions), by multiplying the selectivity of each restriction 
 *    by the original size of the relation.  
 *    
 *    Sets the 'size' field for each relation entry with this computed size.
 *    
 * Returns the size.
 */
int compute_rel_size(Rel *rel)
{
    Cost temp;
    int temp1;

    temp = rel->tuples * product_selec(rel->clauseinfo); 
    Assert(temp >= 0);
    if (temp >= (MAXINT - 1)) {
	temp1 = MAXINT;
    } else {
	temp1 = ceil((double) temp);
    }
    Assert(temp1 >= 0);
    Assert(temp1 <= MAXINT);
    return(temp1);
}

/*    
 * compute-rel-width--
 *    Computes the width in bytes of a tuple from 'rel'.
 *    
 * Returns the width of the tuple as a fixnum.
 */
int
compute_rel_width(Rel *rel)
{
    return (compute_targetlist_width(get_actual_tlist(rel->targetlist)));
}

/*    
 * compute-targetlist-width--
 *    Computes the width in bytes of a tuple made from 'targetlist'.
 *    
 * Returns the width of the tuple as a fixnum.
 */
int
compute_targetlist_width(List *targetlist)
{
    List *temp_tl;
    int tuple_width = 0;

    foreach (temp_tl, targetlist) {
	tuple_width = tuple_width + 
	    compute_attribute_width(lfirst(temp_tl));
    }
    return(tuple_width);
}

/*    
 * compute-attribute-width--
 *    Given a target list entry, find the size in bytes of the attribute.
 *    
 *    If a field is variable-length, it is assumed to be at least the size
 *    of a TID field.
 *    
 * Returns the width of the attribute as a fixnum.
 */
static int
compute_attribute_width(TargetEntry *tlistentry)
{
    int width = get_typlen(tlistentry->resdom->restype);
    if (width < 0) 
	return(_DEFAULT_ATTRIBUTE_WIDTH_);
    else 
	return(width);
}

/*    
 * compute-joinrel-size--
 *    Computes the size of the join relation 'joinrel'.
 *    
 * Returns a fixnum.
 */
int
compute_joinrel_size(JoinPath *joinpath)
{
    Cost temp = 1.0;
    int temp1 = 0;

    temp *= ((Path*)joinpath->outerjoinpath)->parent->size;
    temp *= ((Path*)joinpath->innerjoinpath)->parent->size;
		      
    temp = temp * product_selec(joinpath->pathclauseinfo);
    if (temp >= (MAXINT -1)) {
	temp1 = MAXINT;
    } else {
	/* should be ceil here, we don't want joinrel size's of one, do we? */
	temp1 = ceil((double)temp);
    }
    Assert(temp1 >= 0);

    return(temp1);
}

/*    
 * page-size--
 *    Returns an estimate of the number of pages covered by a given
 *    number of tuples of a given width (size in bytes).
 */
int page_size(int tuples, int width)
{
    int temp =0;

    temp = ceil((double)(tuples * (width + sizeof(HeapTupleData))) 
		/ BLCKSZ);
    Assert(temp >= 0);
    return(temp);
}

static double
base_log(double x, double b)
{
    return(log(x)/log(b));
}