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MDEV-5985: EITS: selectivity estimates look illogical for join and non-key equalities

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Part#1. 

table_cond_selectivity() should discount selectivity of table' 
conditions only when ity counts that selectivity to begin with. 

For non-ref-based access methods (ALL/range/index_merge/etc),
we start with sel=1.0 and hence do not need to discount any
selectivities.
This commit is contained in:
Sergey Petrunya
2014-06-10 12:25:16 +02:00
parent 349e31d5a7
commit aeb62282a2
3 changed files with 75 additions and 13 deletions
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33
sql/sql_select.cc
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@ -7436,21 +7436,28 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
If the field f from the table is equal to a field from one the
earlier joined tables then the selectivity of the range conditions
over the field f must be discounted.
*/
for (Field **f_ptr=table->field ; (field= *f_ptr) ; f_ptr++)
We need to discount selectivity only if we're using ref-based
access method (and have sel!=1).
If we use ALL/range/index_merge, then sel==1, and no need to discount.
*/
if (pos->key != NULL)
{
if (!bitmap_is_set(read_set, field->field_index) ||
!field->next_equal_field)
continue;
for (Field *next_field= field->next_equal_field;
next_field != field;
next_field= next_field->next_equal_field)
for (Field **f_ptr=table->field ; (field= *f_ptr) ; f_ptr++)
{
if (!(next_field->table->map & rem_tables) && next_field->table != table)
{
if (field->cond_selectivity > 0)
sel/= field->cond_selectivity;
break;
if (!bitmap_is_set(read_set, field->field_index) ||
!field->next_equal_field)
continue;
for (Field *next_field= field->next_equal_field;
next_field != field;
next_field= next_field->next_equal_field)
{
if (!(next_field->table->map & rem_tables) && next_field->table != table)
{
if (field->cond_selectivity > 0)
sel/= field->cond_selectivity;
break;
}
}
}
}