Drizzled Public API Documentation

drizzled::optimizer::Position Class Reference

#include <position.h>

Public Member Functions

 Position (double in_records_read, double in_read_time, JoinTable *in_table, KeyUse *in_key, table_map in_ref_depend_map)
 
 Position (const Position &rhs)
 
Positionoperator= (const Position &rhs)
 
bool isConstTable () const
 
double getFanout () const
 
void setFanout (double in_records_read)
 
double getCost () const
 
JoinTablegetJoinTable ()
 
bool hasTableForSorting (Table *cmp_table) const
 
bool examinePosition (table_map found_ref)
 
KeyUsegetKeyUse ()
 
table_map getRefDependMap () const
 
void clearRefDependMap ()
 

Private Attributes

double records_read
 
double read_time
 
JoinTabletable
 
KeyUsekey
 
table_map ref_depend_map
 

Detailed Description

Information about a position of table within a join order. Used in join optimization.

Definition at line 33 of file position.h.

Member Function Documentation

bool drizzled::optimizer::Position::hasTableForSorting ( Table cmp_table) const
inline

Check to see if the table attached to the JoinTable for this position has an index that can produce an ordering.

Returns
true if the table attached to the JoinTable for this position does not have an index that can produce an ordering; false otherwise

Definition at line 128 of file position.h.

Referenced by drizzled::best_extension_by_limited_search(), and drizzled::optimize_straight_join().

bool drizzled::optimizer::Position::isConstTable ( ) const
inline

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.

Returns
true if this position represents a const table; false otherwise

Definition at line 96 of file position.h.

References records_read.

Referenced by drizzled::best_extension_by_limited_search().

Member Data Documentation

KeyUse* drizzled::optimizer::Position::key
private

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}

Definition at line 172 of file position.h.

double drizzled::optimizer::Position::read_time
private

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.

Definition at line 164 of file position.h.

double drizzled::optimizer::Position::records_read
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.

Definition at line 157 of file position.h.

Referenced by isConstTable().

table_map drizzled::optimizer::Position::ref_depend_map
private

If ref-based access is used: bitmap of tables this table depends on

Definition at line 175 of file position.h.


The documentation for this class was generated from the following files: