database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2026-01-06 05:22:24 +03:00
Code Activity

Make first_value and last_value computation efficient

Browse Source 
With clever use of partition bounds, we only need to add one row to the
items at a time. This way we remove the need to "reset" the item and run
through the full partition again.
This commit is contained in:
Vicențiu Ciorbaru
2016-09-20 22:12:48 +02:00
parent 15b8a772cc
commit a2bafbabe2
2 changed files with 91 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

105
sql/sql_window.cc
View File

@@ -824,6 +824,17 @@ protected:
}
}
/* Clear all sum functions handled by this cursor. */
void clear_sum_functions()
{
List_iterator_fast<Item_sum> iter_sum_func(sum_functions);
Item_sum *sum_func;
while ((sum_func= iter_sum_func++))
{
sum_func->clear();
}
}
/* Sum functions that this cursor handles. */
List<Item_sum> sum_functions;
@@ -1847,17 +1858,6 @@ private:
Table_read_cursor cursor;
ha_rows curr_rownum;
/* Clear all sum functions handled by this cursor. */
void clear_sum_functions()
{
List_iterator_fast<Item_sum> iter_sum_func(sum_functions);
Item_sum *sum_func;
while ((sum_func= iter_sum_func++))
{
sum_func->clear();
}
}
/* Scan the rows between the top bound and bottom bound. Add all the values
between them, top bound row and bottom bound row inclusive. */
void compute_values_for_current_row()
@@ -1883,6 +1883,55 @@ private:
}
};
/* A cursor that follows a target cursor. Each time a new row is added,
the window functions are cleared and only have the row at which the target
is point at added to them.
*/
class Frame_positional_cursor : public Frame_cursor
{
public:
Frame_positional_cursor(const Frame_cursor &position_cursor) :
position_cursor(position_cursor) {}
void init(READ_RECORD *info)
{
cursor.init(info);
}
void pre_next_partition(ha_rows rownum)
{
clear_sum_functions();
}
void next_partition(ha_rows rownum)
{
cursor.move_to(position_cursor.get_curr_rownum());
add_value_to_items();
}
void pre_next_row()
{
}
void next_row()
{
if (position_cursor.is_outside_computation_bounds())
clear_sum_functions();
cursor.move_to(position_cursor.get_curr_rownum());
add_value_to_items();
}
ha_rows get_curr_rownum() const
{
return position_cursor.get_curr_rownum();
}
private:
const Frame_cursor &position_cursor;
Table_read_cursor cursor;
};
/*
Get a Frame_cursor for a frame bound. This is a "factory function".
@@ -1990,8 +2039,9 @@ Frame_cursor *get_frame_cursor(THD *thd, Window_spec *spec, bool is_top_bound)
return NULL;
}
void add_extra_frame_cursors(THD *thd, Cursor_manager *cursor_manager,
Item_window_func *window_func)
static
void add_special_frame_cursors(THD *thd, Cursor_manager *cursor_manager,
Item_window_func *window_func)
{
Window_spec *spec= window_func->window_spec;
Item_sum *item_sum= window_func->window_func();
@@ -2010,6 +2060,19 @@ void add_extra_frame_cursors(THD *thd, Cursor_manager *cursor_manager,
fc->add_sum_func(item_sum);
cursor_manager->add_cursor(fc);
break;
case Item_sum::FIRST_VALUE_FUNC:
fc= get_frame_cursor(thd, spec, true);
fc->set_no_action();
cursor_manager->add_cursor(fc);
fc= new Frame_positional_cursor(*fc);
fc->add_sum_func(item_sum);
cursor_manager->add_cursor(fc);
break;
case Item_sum::LAST_VALUE_FUNC:
fc= get_frame_cursor(thd, spec, false);
fc->add_sum_func(item_sum);
cursor_manager->add_cursor(fc);
break;
default:
fc= new Frame_unbounded_preceding(
thd, spec->partition_list, spec->order_list);
@@ -2032,6 +2095,8 @@ static bool is_computed_with_remove(Item_sum::Sumfunctype sum_func)
case Item_sum::RANK_FUNC:
case Item_sum::DENSE_RANK_FUNC:
case Item_sum::NTILE_FUNC:
case Item_sum::FIRST_VALUE_FUNC:
case Item_sum::LAST_VALUE_FUNC:
return false;
default:
return true;
@@ -2071,12 +2136,20 @@ void get_window_functions_required_cursors(
/*
If it is not a regular window function that follows frame specifications,
specific cursors are required. ROW_NUM, RANK, NTILE and others follow
such rules. Check is_frame_prohibited check for the full list.
and/or specific cursors are required. ROW_NUM, RANK, NTILE and others
follow such rules. Check is_frame_prohibited check for the full list.
TODO(cvicentiu) This approach is messy. Every time a function allows
computation in a certain way, we have to add an extra method to this
factory function. It is better to have window functions output
their own cursors, as needed. This way, the logic is bound
only to the implementation of said window function. Regular aggregate
functions can keep the default frame generating code, overwrite it or
add to it.
*/
if (item_win_func->is_frame_prohibited())
{
add_extra_frame_cursors(thd, cursor_manager, item_win_func);
add_special_frame_cursors(thd, cursor_manager, item_win_func);
cursor_managers->push_back(cursor_manager);
continue;
}