~drizzle-trunk/drizzle/development

/* -*- 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 */