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/* -*- mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; -*-
* vim:expandtab:shiftwidth=2:tabstop=2:smarttab:
*
* Copyright (C) 2009 Sun Microsystems, Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#pragma once
#include <drizzled/join_table.h>
namespace drizzled
{
namespace optimizer
{
/**
* Information about a position of table within a join order. Used in join
* optimization.
*/
class Position
{
public:
Position()
:
records_read(0),
read_time(0),
table(NULL),
key(NULL),
ref_depend_map(0)
{}
Position(double in_records_read,
double in_read_time,
JoinTable *in_table,
KeyUse *in_key,
table_map in_ref_depend_map)
:
records_read(in_records_read),
read_time(in_read_time),
table(in_table),
key(in_key),
ref_depend_map(in_ref_depend_map)
{}
Position(const Position &rhs)
:
records_read(rhs.records_read),
read_time(rhs.read_time),
table(rhs.table),
key(rhs.key),
ref_depend_map(rhs.ref_depend_map)
{}
Position &operator=(const Position &rhs)
{
if (this == &rhs)
{
return *this;
}
records_read= rhs.records_read;
read_time= rhs.read_time;
table= rhs.table;
key= rhs.key;
ref_depend_map= rhs.ref_depend_map;
return *this;
}
/**
* Determine whether the table this particular position is representing in
* the query plan is a const table or not. A constant table is defined as
* (taken from the MySQL optimizer internals document on MySQL forge):
*
* 1) A table with zero rows, or with only one row
* 2) A table expression that is restricted with a WHERE condition
*
* Based on the definition above, when records_read is set to 1.0 in the
* Position class, it infers that this position in the partial plan
* represents a const table.
*
* @return true if this position represents a const table; false otherwise
*/
bool isConstTable() const
{
return (records_read < 2.0);
}
double getFanout() const
{
return records_read;
}
void setFanout(double in_records_read)
{
records_read= in_records_read;
}
double getCost() const
{
return read_time;
}
JoinTable *getJoinTable()
{
return table;
}
/**
* Check to see if the table attached to the JoinTable for this position
* has an index that can produce an ordering.
*
* @return true if the table attached to the JoinTable for this position
* does not have an index that can produce an ordering; false otherwise
*/
bool hasTableForSorting(Table *cmp_table) const
{
return (cmp_table != table->table);
}
bool examinePosition(table_map found_ref);
KeyUse *getKeyUse()
{
return key;
}
table_map getRefDependMap() const
{
return ref_depend_map;
}
void clearRefDependMap()
{
ref_depend_map= 0;
}
private:
/**
The "fanout": number of output rows that will be produced (after
pushed down selection condition is applied) per each row combination of
previous tables. The value is an in-precise estimate.
*/
double records_read;
/**
Cost accessing the table in course of the entire complete join execution,
i.e. cost of one access method use (e.g. 'range' or 'ref' scan ) times
number the access method will be invoked.
*/
double read_time;
JoinTable *table;
/**
NULL - 'index' or 'range' or 'index_merge' or 'ALL' access is used.
Other - [eq_]ref[_or_null] access is used. Pointer to {t.keypart1 = expr}
*/
KeyUse *key;
/** If ref-based access is used: bitmap of tables this table depends on */
table_map ref_depend_map;
};
} /* end namespace optimizer */
} /* end namespace drizzled */
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