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Fixed bug mdev-277 as part of the fix for lp:944706

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The cause for this bug is that the method JOIN::get_examined_rows iterates over all
JOIN_TABs of the join assuming they are just a sequence. In the query above, the
innermost subquery is merged into its parent query. When we call
JOIN::get_examined_rows for the second-level subquery, the iteration that
assumes sequential order of join tabs goes outside the join_tab array and calls
the method JOIN_TAB::get_examined_rows on uninitialized memory. 

The fix is to iterate over JOIN_TABs in a way that takes into account the nested
semi-join structure of JOIN_TABs. In particular iterate as select_describe.
This commit is contained in:
unknown
2012-05-18 14:52:01 +03:00
parent da5214831d
commit e5bca74bfb
7 changed files with 133 additions and 9 deletions
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19
sql/sql_select.cc
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@ -270,6 +270,8 @@ Item_equal *find_item_equal(COND_EQUAL *cond_equal, Field *field,
bool *inherited_fl);
JOIN_TAB *first_depth_first_tab(JOIN* join);
JOIN_TAB *next_depth_first_tab(JOIN* join, JOIN_TAB* tab);
JOIN_TAB *first_breadth_first_tab(JOIN *join);
JOIN_TAB *next_breadth_first_tab(JOIN *join, JOIN_TAB *tab);
/**
This handles SELECT with and without UNION.
@ -6615,19 +6617,18 @@ void JOIN::get_prefix_cost_and_fanout(uint n_tables,
double JOIN::get_examined_rows()
{
/* Each constant table examines one row, and the result is at most one row. */
ha_rows examined_rows= const_tables;
uint i= const_tables;
ha_rows examined_rows;
double prev_fanout= 1;
JOIN_TAB *tab= first_breadth_first_tab(this);
JOIN_TAB *prev_tab= tab;
if (table_count == const_tables)
return examined_rows;
examined_rows= tab->get_examined_rows();
examined_rows+= join_tab[i++].get_examined_rows();
for (; i < table_count ; i++)
while ((tab= next_breadth_first_tab(this, tab)))
{
prev_fanout *= best_positions[i-1].records_read;
examined_rows+= join_tab[i].get_examined_rows() * prev_fanout;
prev_fanout *= prev_tab->records_read;
examined_rows+= tab->get_examined_rows() * prev_fanout;
prev_tab= tab;
}
return examined_rows;
}