MySQL Cost-Based Optimizer 模型
MySQL Cost_estimate 定义了多种消耗类型
1. io_cost cost of I/O operations IO操作消耗
2. cpu_cost cost of CPU operations CPU操作消耗
3. import_cost cost of remote operations 远程操作消耗
4. mem_cost memory used (bytes) 内存消耗
KEY_COMPARE_COST= 0.1
MEMORY_TEMPTABLE_CREATE_COST= 2.0
MEMORY_TEMPTABLE_ROW_COST= 0.2
DISK_TEMPTABLE_CREATE_COST= 40.0
DISK_TEMPTABLE_ROW_COST= 1.0
ROW_EVALUATE_COST= 0.2
MEMORY_BLOCK_READ_COST= 1.0
IO_BLOCK_READ_COST= 1.0
io_block_read_cost
memory_block_read_cost
disk_temptable_create_cost
disk_temptable_row_cost
key_compare_cost
memory_temptable_create_cost
memory_temptable_row_cost
row_evaluate_cost
MySQL目前版本只使用了 io_cost,cpu_cost
io_cost 定义了以下三种方法: 表扫、索引扫、读取消耗
Cost_estimate handler::table_scan_cost()
{
/*
This function returns a Cost_estimate object. The function should be
implemented in a way that allows the compiler to use "return value
optimization" to avoid creating the temporary object for the return value
and use of the copy constructor.
*/
const double io_cost= scan_time() * table->cost_model()->page_read_cost(1.0);
Cost_estimate cost;
cost.add_io(io_cost);
return cost;
}
Cost_estimate handler::index_scan_cost(uint index, double ranges, double rows)
{
/*
This function returns a Cost_estimate object. The function should be
implemented in a way that allows the compiler to use "return value
optimization" to avoid creating the temporary object for the return value
and use of the copy constructor.
*/
DBUG_ASSERT(ranges >= 0.0);
DBUG_ASSERT(rows >= 0.0);
const double io_cost= index_only_read_time(index, rows) *
table->cost_model()->page_read_cost_index(index, 1.0);
Cost_estimate cost;
cost.add_io(io_cost);
return cost;
}
Cost_estimate handler::read_cost(uint index, double ranges, double rows)
{
/*
This function returns a Cost_estimate object. The function should be
implemented in a way that allows the compiler to use "return value
optimization" to avoid creating the temporary object for the return value
and use of the copy constructor.
*/
DBUG_ASSERT(ranges >= 0.0);
DBUG_ASSERT(rows >= 0.0);
const double io_cost= read_time(index, static_cast<uint>(ranges),
static_cast<ha_rows>(rows)) *
table->cost_model()->page_read_cost(1.0);
Cost_estimate cost;
cost.add_io(io_cost);
return cost;
}
cpu_cost
MySQL Cost-Based Optimizer 模型
MySQL Cost_estimate 定义了多种消耗类型
1. io_cost cost of I/O operations IO操作消耗
2. cpu_cost cost of CPU operations CPU操作消耗
3. import_cost cost of remote operations 远程操作消耗
4. mem_cost memory used (bytes) 内存消耗
KEY_COMPARE_COST= 0.1
MEMORY_TEMPTABLE_CREATE_COST= 2.0
MEMORY_TEMPTABLE_ROW_COST= 0.2
DISK_TEMPTABLE_CREATE_COST= 40.0
DISK_TEMPTABLE_ROW_COST= 1.0
ROW_EVALUATE_COST= 0.2
MEMORY_BLOCK_READ_COST= 1.0
IO_BLOCK_READ_COST= 1.0
io_block_read_cost
memory_block_read_cost
disk_temptable_create_cost
disk_temptable_row_cost
key_compare_cost
memory_temptable_create_cost
memory_temptable_row_cost
row_evaluate_cost
MySQL目前版本只使用了 io_cost,cpu_cost
io_cost 定义了以下三种方法: 表扫、索引扫、读取消耗
Cost_estimate handler::table_scan_cost()
{
/*
This function returns a Cost_estimate object. The function should be
implemented in a way that allows the compiler to use "return value
optimization" to avoid creating the temporary object for the return value
and use of the copy constructor.
*/
const double io_cost= scan_time() * table->cost_model()->page_read_cost(1.0);
Cost_estimate cost;
cost.add_io(io_cost);
return cost;
}
Cost_estimate handler::index_scan_cost(uint index, double ranges, double rows)
{
/*
This function returns a Cost_estimate object. The function should be
implemented in a way that allows the compiler to use "return value
optimization" to avoid creating the temporary object for the return value
and use of the copy constructor.
*/
DBUG_ASSERT(ranges >= 0.0);
DBUG_ASSERT(rows >= 0.0);
const double io_cost= index_only_read_time(index, rows) *
table->cost_model()->page_read_cost_index(index, 1.0);
Cost_estimate cost;
cost.add_io(io_cost);
return cost;
}
Cost_estimate handler::read_cost(uint index, double ranges, double rows)
{
/*
This function returns a Cost_estimate object. The function should be
implemented in a way that allows the compiler to use "return value
optimization" to avoid creating the temporary object for the return value
and use of the copy constructor.
*/
DBUG_ASSERT(ranges >= 0.0);
DBUG_ASSERT(rows >= 0.0);
const double io_cost= read_time(index, static_cast<uint>(ranges),
static_cast<ha_rows>(rows)) *
table->cost_model()->page_read_cost(1.0);
Cost_estimate cost;
cost.add_io(io_cost);
return cost;
}