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MDEV-5992: EITS: Selectivity of non-indexed condition is counted twice in table's fanout

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MDEV-5984: EITS: Incorrect filtered% value for single-table select with range access
- Fix calculate_cond_selectivity_for_table() to work correctly with range accesses 
  over multi-component keys:
  = First, take selectivity of all possible range scans into account. Remember which 
    fields were used bt the range scans.
  = Then, calculate selectivity produced by sargable predicates on fields. If a 
    field was used in a possible range access, assume its selectivity is already
    taken into account.
- Fix table_cond_selectivity(): when quick select is used, selectivity of
  COND(table) is taken into account in matching_candidates_in_table(). In
  table_cond_selectivity() we should not apply it for the second time.
This commit is contained in:
Sergey Petrunya
2014-04-01 09:59:51 -07:00
parent 41a2ca5c16
commit 26a3d567c9
4 changed files with 173 additions and 60 deletions
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138
sql/opt_range.cc
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@ -3390,6 +3390,17 @@ double records_in_column_ranges(PARAM *param, uint idx,
on the rows of 'table' in the processed query.
The calculated selectivity is assigned to the field table->cond_selectivity.
Selectivity is calculated as a product of selectivities imposed by:
1. possible range accesses. (if multiple range accesses use the same
restrictions on the same field, we make adjustments for that)
2. Sargable conditions on fields for which we have column statistics (if
a field is used in a possible range access, we assume that selectivity
is already provided by the range access' estimates)
3. Reading a few records from the table pages and checking the condition
selectivity (this is used for conditions like "column LIKE '%val%'"
where approaches #1 and #2 do not provide selectivity data).
NOTE
Currently the selectivities of range conditions over different columns are
considered independent.
@ -3415,14 +3426,90 @@ bool calculate_cond_selectivity_for_table(THD *thd, TABLE *table, Item *cond)
if (table->pos_in_table_list->schema_table)
DBUG_RETURN(FALSE);
MY_BITMAP handled_columns;
my_bitmap_map* buf;
if (!(buf= (my_bitmap_map*)thd->alloc(table->s->column_bitmap_size)))
DBUG_RETURN(TRUE);
my_bitmap_init(&handled_columns, buf, table->s->fields, FALSE);
/*
First, take into account possible range accesses.
range access estimates are the most precise, we prefer them to any other
estimate sources.
*/
for (keynr= 0; keynr < table->s->keys; keynr++)
{
if (table->quick_keys.is_set(keynr))
set_if_bigger(max_quick_key_parts, table->quick_key_parts[keynr]);
}
/*
Walk through all indexes, indexes where range access uses more keyparts
go first.
*/
for (uint quick_key_parts= max_quick_key_parts;
quick_key_parts; quick_key_parts--)
{
for (keynr= 0; keynr < table->s->keys; keynr++)
{
if (table->quick_keys.is_set(keynr) &&
table->quick_key_parts[keynr] == quick_key_parts)
{
uint i;
uint used_key_parts= table->quick_key_parts[keynr];
double quick_cond_selectivity= table->quick_rows[keynr] /
table_records;
KEY *key_info= table->key_info + keynr;
KEY_PART_INFO* key_part= key_info->key_part;
/*
Suppose, there are range conditions on two keys
KEY1 (col1, col2)
KEY2 (col3, col2)
we don't want to count selectivity of condition on col2 twice.
First, find the longest key prefix that's made of columns whose
selectivity wasn't already accounted for.
*/
for (i= 0; i < used_key_parts; i++, key_part++)
{
if (bitmap_is_set(&handled_columns, key_part->fieldnr-1))
break;
bitmap_set_bit(&handled_columns, key_part->fieldnr-1);
}
if (i)
{
/*
There is at least 1-column prefix of columns whose selectivity has
not yet been accounted for.
*/
table->cond_selectivity*= quick_cond_selectivity;
if (i != used_key_parts)
{
/*
Range access got us estimate for #used_key_parts.
We need estimate for #(i-1) key parts.
*/
double f1= key_info->actual_rec_per_key(i-1);
double f2= key_info->actual_rec_per_key(i);
table->cond_selectivity*= f1 / f2;
}
}
}
}
}
/*
Second step: calculate the selectivity of the range conditions not
supported by any index
*/
bitmap_subtract(used_fields, &handled_columns);
/* no need to do: my_bitmap_free(&handled_columns); */
if (thd->variables.optimizer_use_condition_selectivity > 2 &&
!bitmap_is_clear_all(used_fields))
{
/*
Calculate the selectivity of the range conditions not supported
by any index
*/
PARAM param;
MEM_ROOT alloc;
SEL_TREE *tree;
@ -3509,47 +3596,8 @@ bool calculate_cond_selectivity_for_table(THD *thd, TABLE *table, Item *cond)
bitmap_clear_all(used_fields);
for (keynr= 0; keynr < table->s->keys; keynr++)
{
if (table->quick_keys.is_set(keynr))
set_if_bigger(max_quick_key_parts, table->quick_key_parts[keynr]);
}
for (uint quick_key_parts= max_quick_key_parts;
quick_key_parts; quick_key_parts--)
{
for (keynr= 0; keynr < table->s->keys; keynr++)
{
if (table->quick_keys.is_set(keynr) &&
table->quick_key_parts[keynr] == quick_key_parts)
{
uint i;
uint used_key_parts= table->quick_key_parts[keynr];
double quick_cond_selectivity= table->quick_rows[keynr] /
table_records;
KEY *key_info= table->key_info + keynr;
KEY_PART_INFO* key_part= key_info->key_part;
for (i= 0; i < used_key_parts; i++, key_part++)
{
if (bitmap_is_set(used_fields, key_part->fieldnr-1))
break;
bitmap_set_bit(used_fields, key_part->fieldnr-1);
}
if (i)
{
table->cond_selectivity*= quick_cond_selectivity;
if (i != used_key_parts)
{
double f1= key_info->actual_rec_per_key(i-1);
double f2= key_info->actual_rec_per_key(i);
table->cond_selectivity*= f1 / f2;
}
}
}
}
}
/* Calculate selectivity of probably highly selective predicates */
/* Check if we can improve selectivity estimates by using sampling */
ulong check_rows=
MY_MIN(thd->variables.optimizer_selectivity_sampling_limit,
(ulong) (table_records * SELECTIVITY_SAMPLING_SHARE));