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BUG#29582: huge memory consumption with union, subselect, joins:

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- Don't call mysql_select() several times for the select that enumerates
  a temporary table with the results of the UNION. Making this call for
  every subquery execution caused O(#enumerated-rows-in-the-outer-query) 
  memory allocations.
- Instead, call join->reinit() and join->exec(), and
  = disable constant table detection for such joins,  
  = provide special handling for table-less constant subqueries.


sql/sql_select.cc:
  BUG#29582: huge memory consumption with union, subselect, joins:
   - Don't mark tables as constant if JOIN::no_const_tables flag is set
sql/sql_select.h:
  BUG#29582: huge memory consumption with union, subselect, joins:
   - Don't mark tables as constant if JOIN::no_const_tables flag is set
sql/sql_union.cc:
  BUG#29582: huge memory consumption with union, subselect, joins:
  - Don't call mysql_select() several times for the select that enumerates
    a temporary table with UNION results. 
  - Instead, call join->reinit() and join->exec().
  - Provide special handling for table-less constant subqueries.
This commit is contained in:
unknown
2007-07-31 15:19:06 +04:00
parent 2679e53a73
commit 8a68e7d2dc
3 changed files with 51 additions and 18 deletions
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57
sql/sql_union.cc
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@@ -545,6 +545,10 @@ bool st_select_lex_unit::exec()
/*
allocate JOIN for fake select only once (prevent
mysql_select automatic allocation)
TODO: The above is nonsense. mysql_select() will not allocate the
join if one already exists. There must be some other reason why we
don't let it allocate the join. Perhaps this is because we need
some special parameter values passed to join constructor?
*/
if (!(fake_select_lex->join= new JOIN(thd, item_list,
fake_select_lex->options, result)))
@@ -552,33 +556,52 @@ bool st_select_lex_unit::exec()
fake_select_lex->table_list.empty();
DBUG_RETURN(TRUE);
}
fake_select_lex->join->no_const_tables= TRUE;
/*
Fake st_select_lex should have item list for correctref_array
allocation.
*/
fake_select_lex->item_list= item_list;
saved_error= mysql_select(thd, &fake_select_lex->ref_pointer_array,
&result_table_list,
0, item_list, NULL,
global_parameters->order_list.elements,
(ORDER*)global_parameters->order_list.first,
(ORDER*) NULL, NULL, (ORDER*) NULL,
fake_select_lex->options | SELECT_NO_UNLOCK,
result, this, fake_select_lex);
}
else
{
JOIN_TAB *tab,*end;
for (tab=join->join_tab, end=tab+join->tables ;
tab && tab != end ;
tab++)
{
delete tab->select;
delete tab->quick;
}
join->init(thd, item_list, fake_select_lex->options, result);
if (describe)
{
/*
In EXPLAIN command, constant subqueries that do not use any
tables are executed two times:
- 1st time is a real evaluation to get the subquery value
- 2nd time is to produce EXPLAIN output rows.
1st execution sets certain members (e.g. select_result) to perform
subquery execution rather than EXPLAIN line production. In order
to reset them back, we re-do all of the actions (yes it is ugly):
*/
join->init(thd, item_list, fake_select_lex->options, result);
saved_error= mysql_select(thd, &fake_select_lex->ref_pointer_array,
&result_table_list,
0, item_list, NULL,
global_parameters->order_list.elements,
(ORDER*)global_parameters->order_list.first,
(ORDER*) NULL, NULL, (ORDER*) NULL,
fake_select_lex->options | SELECT_NO_UNLOCK,
result, this, fake_select_lex);
}
else
{
join->examined_rows= 0;
join->reinit();
saved_error= join->exec();
}
}
saved_error= mysql_select(thd, &fake_select_lex->ref_pointer_array,
&result_table_list,
0, item_list, NULL,
global_parameters->order_list.elements,
(ORDER*)global_parameters->order_list.first,
(ORDER*) NULL, NULL, (ORDER*) NULL,
fake_select_lex->options | SELECT_NO_UNLOCK,
result, this, fake_select_lex);
fake_select_lex->table_list.empty();
if (!saved_error)