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Commit 182f7d76 authored by Sergey Petrunya's avatar Sergey Petrunya
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Revert these two changes (wrong push) : 

MDEV-5980: EITS: if condition is used for REF access, its selectivity is still in filtered%
MDEV-5985: EITS: selectivity estimates look illogical for join and non-key equalities
MDEV-6003: EITS: ref access, keypart2=const vs keypart2=expr - inconsistent filtered% value
- Made a number of fixes in table_cond_selectivity() so that it returns
  correct selectivity estimates.
- Added comments in related code.
Better comments
parent 46d1b845
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Showing with 14 additions and 346 deletions
mysql-test/r/selectivity_no_engine.result
View file @ 182f7d76
......@@ -139,118 +139,6 @@ Warnings:
Note 1003 select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`col1` AS `col1`,`test`.`t2`.`col2` AS `col2` from `test`.`t2` where ((`test`.`t2`.`a` in (1,2,3)) and (`test`.`t2`.`b` in (1,2,3)))
drop table t2, t1;
#
# MDEV-5980: EITS: if condition is used for REF access, its selectivity is still in filtered%
#
create table t0(a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1(key1 int, col1 int, key(key1));
insert into t1 select A.a, A.a from t0 A, t0 B, t0 C;
set histogram_size=100;
set use_stat_tables='preferably';
set optimizer_use_condition_selectivity=4;
analyze table t1 persistent for all;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status Table is already up to date
# 10% is ok
explain extended select * from t1 where col1=2;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 1000 9.90 Using where
Warnings:
Note 1003 select `test`.`t1`.`key1` AS `key1`,`test`.`t1`.`col1` AS `col1` from `test`.`t1` where (`test`.`t1`.`col1` = 2)
# Must show 100%, not 10%
explain extended select * from t1 where key1=2;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ref key1 key1 5 const 98 100.00
Warnings:
Note 1003 select `test`.`t1`.`key1` AS `key1`,`test`.`t1`.`col1` AS `col1` from `test`.`t1` where (`test`.`t1`.`key1` = 2)
drop table t0, t1;
#
# MDEV-5985: EITS: selectivity estimates look illogical for join and non-key equalities
#
create table t1(a int);
insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t2(a int);
insert into t2 select A.a + B.a* 10 + C.a * 100 from t1 A, t1 B, t1 C;
create table t3 as select * from t2;
set histogram_size=100;
set use_stat_tables='preferably';
set optimizer_use_condition_selectivity=4;
analyze table t2 persistent for all;
Table Op Msg_type Msg_text
test.t2 analyze status Engine-independent statistics collected
test.t2 analyze status OK
analyze table t3 persistent for all;
Table Op Msg_type Msg_text
test.t3 analyze status Engine-independent statistics collected
test.t3 analyze status OK
explain extended select * from t2 A where A.a < 40;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE A ALL NULL NULL NULL NULL 1000 4.95 Using where
Warnings:
Note 1003 select `test`.`A`.`a` AS `a` from `test`.`t2` `A` where (`test`.`A`.`a` < 40)
explain extended select * from t3 B where B.a < 100;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE B ALL NULL NULL NULL NULL 1000 9.90 Using where
Warnings:
Note 1003 select `test`.`B`.`a` AS `a` from `test`.`t3` `B` where (`test`.`B`.`a` < 100)
explain extended select * from t2 A, t3 B where A.a < 40 and B.a < 100;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE A ALL NULL NULL NULL NULL 1000 4.95 Using where
1 SIMPLE B ALL NULL NULL NULL NULL 1000 9.90 Using where; Using join buffer (flat, BNL join)
Warnings:
Note 1003 select `test`.`A`.`a` AS `a`,`test`.`B`.`a` AS `a` from `test`.`t2` `A` join `test`.`t3` `B` where ((`test`.`A`.`a` < 40) and (`test`.`B`.`a` < 100))
explain extended select * from t2 A, t3 B where A.a < 40 and B.a < 100 and B.a=A.a;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE A ALL NULL NULL NULL NULL 1000 4.95 Using where
1 SIMPLE B ALL NULL NULL NULL NULL 1000 4.95 Using where; Using join buffer (flat, BNL join)
Warnings:
Note 1003 select `test`.`A`.`a` AS `a`,`test`.`B`.`a` AS `a` from `test`.`t2` `A` join `test`.`t3` `B` where ((`test`.`B`.`a` = `test`.`A`.`a`) and (`test`.`A`.`a` < 40) and (`test`.`A`.`a` < 100))
drop table t1, t2, t3;
select 1;
1
1
#
# MDEV-6003: EITS: ref access, keypart2=const vs keypart2=expr - inconsistent filtered% value
#
create table t0(a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1 (
kp1 int, kp2 int,
filler1 char(100),
filler2 char(100),
key(kp1, kp2)
);
insert into t1
select
A.a,
B.a,
'filler-data-1',
'filler-data-2'
from t0 A, t0 B, t0 C;
set histogram_size=100;
set use_stat_tables='preferably';
set optimizer_use_condition_selectivity=4;
analyze table t1 persistent for all;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status Table is already up to date
# NOTE: 10*100%, 10*100% rows is ok
explain extended select * from t0, t1 where t1.kp1=t0.a and t1.kp2=t0.a+1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t0 ALL NULL NULL NULL NULL 10 100.00 Using where
1 SIMPLE t1 ref kp1 kp1 10 test.t0.a,func 10 100.00 Using index condition
Warnings:
Note 1003 select `test`.`t0`.`a` AS `a`,`test`.`t1`.`kp1` AS `kp1`,`test`.`t1`.`kp2` AS `kp2`,`test`.`t1`.`filler1` AS `filler1`,`test`.`t1`.`filler2` AS `filler2` from `test`.`t0` join `test`.`t1` where ((`test`.`t1`.`kp1` = `test`.`t0`.`a`) and (`test`.`t1`.`kp2` = (`test`.`t0`.`a` + 1)))
# NOTE: t0: 10*100% is ok, t1: 10*9.90% is bad. t1 should have 10*100%.
explain extended select * from t0, t1 where t1.kp1=t0.a and t1.kp2=4;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t0 ALL NULL NULL NULL NULL 10 100.00 Using where
1 SIMPLE t1 ref kp1 kp1 10 test.t0.a,const 10 100.00
Warnings:
Note 1003 select `test`.`t0`.`a` AS `a`,`test`.`t1`.`kp1` AS `kp1`,`test`.`t1`.`kp2` AS `kp2`,`test`.`t1`.`filler1` AS `filler1`,`test`.`t1`.`filler2` AS `filler2` from `test`.`t0` join `test`.`t1` where ((`test`.`t1`.`kp1` = `test`.`t0`.`a`) and (`test`.`t1`.`kp2` = 4))
drop table t0, t1;
#
# End of the test file
#
set use_stat_tables= @save_use_stat_tables;
......
mysql-test/t/selectivity_no_engine.test
View file @ 182f7d76
......@@ -101,78 +101,6 @@ analyze table t2 persistent for all;
explain extended select * from t2 where a in (1,2,3) and b in (1,2,3);
drop table t2, t1;
--echo #
--echo # MDEV-5980: EITS: if condition is used for REF access, its selectivity is still in filtered%
--echo #
create table t0(a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1(key1 int, col1 int, key(key1));
insert into t1 select A.a, A.a from t0 A, t0 B, t0 C;
set histogram_size=100;
set use_stat_tables='preferably';
set optimizer_use_condition_selectivity=4;
analyze table t1 persistent for all;
--echo # 10% is ok
explain extended select * from t1 where col1=2;
--echo # Must show 100%, not 10%
explain extended select * from t1 where key1=2;
drop table t0, t1;
##--disable_parsing
--echo #
--echo # MDEV-5985: EITS: selectivity estimates look illogical for join and non-key equalities
--echo #
create table t1(a int);
insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t2(a int);
insert into t2 select A.a + B.a* 10 + C.a * 100 from t1 A, t1 B, t1 C;
create table t3 as select * from t2;
set histogram_size=100;
set use_stat_tables='preferably';
set optimizer_use_condition_selectivity=4;
analyze table t2 persistent for all;
analyze table t3 persistent for all;
explain extended select * from t2 A where A.a < 40;
explain extended select * from t3 B where B.a < 100;
explain extended select * from t2 A, t3 B where A.a < 40 and B.a < 100;
explain extended select * from t2 A, t3 B where A.a < 40 and B.a < 100 and B.a=A.a;
drop table t1, t2, t3;
## --enable_parsing
select 1;
##--disable_parsing
--echo #
--echo # MDEV-6003: EITS: ref access, keypart2=const vs keypart2=expr - inconsistent filtered% value
--echo #
create table t0(a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1 (
kp1 int, kp2 int,
filler1 char(100),
filler2 char(100),
key(kp1, kp2)
);
insert into t1
select
A.a,
B.a,
'filler-data-1',
'filler-data-2'
from t0 A, t0 B, t0 C;
set histogram_size=100;
set use_stat_tables='preferably';
set optimizer_use_condition_selectivity=4;
analyze table t1 persistent for all;
--echo # NOTE: 10*100%, 10*100% rows is ok
explain extended select * from t0, t1 where t1.kp1=t0.a and t1.kp2=t0.a+1;
--echo # NOTE: t0: 10*100% is ok, t1: 10*9.90% is bad. t1 should have 10*100%.
explain extended select * from t0, t1 where t1.kp1=t0.a and t1.kp2=4;
drop table t0, t1;
##--enable_parsing
--echo #
--echo # End of the test file
--echo #
......
sql/opt_range.cc
View file @ 182f7d76
......@@ -3406,10 +3406,6 @@ double records_in_column_ranges(PARAM *param, uint idx,
selectivity (this is used for conditions like "column LIKE '%val%'"
where approaches #1 and #2 do not provide selectivity data).
SEE ALSO
table_cond_selectivity()
matching_candidates_in_table()
NOTE
Currently the selectivities of range conditions over different columns are
considered independent.
......
sql/sql_select.cc
View file @ 182f7d76
......@@ -7135,15 +7135,6 @@ double JOIN::get_examined_rows()
@param rem_tables The bitmap of tables to be joined later
@param keyparts The number of key parts to used when joining s
@param ref_keyuse_steps Array of references to keyuses employed to join s
@detail
Basic idea: if the WHERE clause has an equality in form
tbl.column= ...
then this condition will have selectivity 1/#distinct_values(tbl.column),
unless the equality was used by ref access. If the equality is used by ref
access, we only get rows that satisfy it, and so its selectivity=1.
*/
static
......@@ -7174,18 +7165,8 @@ double table_multi_eq_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
the current value of sel by this selectivity
*/
table_map used_tables= item_equal->used_tables();
/*
Equalities that do not include fields in this table do not matter
*/
if (!(used_tables & table_bit))
continue;
/*
Equalities that include a constant are taken into account in
table->cond_selectivity. Selectivity from there is taken into account
in matching_candidates_in_table() and/or table_cond_selectivity().
*/
if (item_equal->get_const())
continue;
......@@ -7197,23 +7178,14 @@ double table_multi_eq_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
Field *fld= fi.get_curr_field();
if (fld->table->map != table_bit)
continue;
if (pos->key == 0)
{
/*
No ref access used (and no const in the multi-equality). We will
need to adjust the selectivity.
*/
adjust_sel= TRUE;
}
else
{
/* Ok, [eq]ref access is used */
uint i;
KEYUSE *keyuse= pos->key;
uint key= keyuse->key;
/* Find which keypart participates in the equality */
for (i= 0; i < keyparts; i++)
{
uint fldno;
......@@ -7224,7 +7196,6 @@ double table_multi_eq_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
if (fld->field_index == fldno)
break;
}
if (i == keyparts)
{
/*
......@@ -7250,7 +7221,6 @@ double table_multi_eq_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
}
}
}
if (adjust_sel)
{
/*
......@@ -7296,10 +7266,6 @@ double table_multi_eq_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
For other access methods, we need to calculate selectivity of the whole
condition, "COND(this_table) AND COND(this_table, previous_tables)".
@seealso
calculate_cond_selectivity_for_table()
matching_candidates_in_table()
@retval
selectivity of the conditions imposed on the rows of s
......@@ -7310,90 +7276,34 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
table_map rem_tables)
{
uint16 ref_keyuse_steps[MAX_REF_PARTS - 1];
Field *field;
TABLE *table= s->table;
double sel;
MY_BITMAP *read_set= table->read_set;
double sel= s->table->cond_selectivity;
POSITION *pos= &join->positions[idx];
uint keyparts= 0;
uint found_part_ref_or_null= 0;
if (pos->key != 0)
{
sel= s->table->cond_selectivity;
/*
A ref access or hash join is used for this table. ref access is created
from
A ref access or hash join is used for this table.
tbl.keypart1=expr1 AND tbl.keypart2=expr2 AND ...
and it will only return rows for which this condition is satisified.
Suppose, certain expr{i} is a constant. Since ref access only returns
rows that satisfy
tbl.keypart{i}=const (*)
then selectivity of this equality should not be counted in return value
of this function. This function uses the value of
table->cond_selectivity=selectivity(COND(tbl)) (**)
as a starting point. This value includes selectivity of equality (*). We
should somehow discount it.
Looking at calculate_cond_selectivity_for_table(), one can see that that
the value is not necessarily a direct multiplicand in
table->cond_selectivity
There are three possible ways to discount
1. There is a potential range access on t.keypart{i}=const.
(an important special case: the used ref access has a const prefix for
which a range estimate is available)
It could have some parts with "t.key_part=const". Using ref access
means that we will only get records where the condition holds, so we
should remove its selectivity from the condition selectivity.
2. The field has a histogram. field[x]->cond_selectivity has the data.
3. Use index stats on this index:
rec_per_key[key_part+1]/rec_per_key[key_part]
(TODO: more details about the "t.key=othertable.col" case)
*/
KEYUSE *keyuse= pos->key;
KEYUSE *prev_ref_keyuse= keyuse;
uint key= keyuse->key;
/*
Check if we have a prefix of key=const that matches a quick select.
*/
if (!is_hash_join_key_no(key))
{
table_map quick_key_map= (table_map(1) << table->quick_key_parts[key]) - 1;
if (table->quick_rows[key] &&
!(quick_key_map & ~table->const_key_parts[key]))
{
/*
Ok, there is an equality for each of the key parts used by the
quick select. This means, quick select's estimate can be reused to
discount the selectivity of a prefix of a ref access.
*/
for (; quick_key_map & 1 ; quick_key_map>>= 1)
{
while (keyuse->keypart == keyparts)
keyuse++;
keyparts++;
}
sel /= table->quick_rows[key] / table->stat_records();
}
}
/*
Go through the "keypart{N}=..." equalities and find those that were
already taken into account in table->cond_selectivity.
*/
while (keyuse->table == table && keyuse->key == key)
do
{
if (!(keyuse->used_tables & (rem_tables | table->map)))
{
if (are_tables_local(s, keyuse->val->used_tables()))
{ /// ^^ why val->used_tables here but just
/// used_tables above?
{
if (is_hash_join_key_no(key))
{
if (keyparts == keyuse->keypart)
......@@ -7402,39 +7312,22 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
else
{
if (keyparts == keyuse->keypart &&
!((keyuse->val->used_tables()) & ~pos->ref_depend_map) &&
!(~(keyuse->val->used_tables()) & pos->ref_depend_map) &&
!(found_part_ref_or_null & keyuse->optimize))
{
/* Found a KEYUSE object that will be used by ref access */
keyparts++;
found_part_ref_or_null|= keyuse->optimize & ~KEY_OPTIMIZE_EQ;
}
}
if (keyparts > keyuse->keypart)
{
/* Ok this is the keyuse that will be used for ref access */
uint fldno;
if (is_hash_join_key_no(key))
fldno= keyuse->keypart;
else
fldno= table->key_info[key].key_part[keyparts-1].fieldnr - 1;
if (keyuse->val->const_item())
{
// psergey: not multiply, divide instead.
// before, we've had:
// sel*= table->field[fldno]->cond_selectivity;
sel /= table->field[fldno]->cond_selectivity;
/*
TODO: we could do better here:
1. cond_selectivity might be =1 (the default) because quick
select on some index prevented us from analyzing
histogram for this column.
2. we could get an estimate through this?
rec_per_key[key_part-1] / rec_per_key[key_part]
*/
}
sel*= table->field[fldno]->cond_selectivity;
if (keyparts > 1)
{
ref_keyuse_steps[keyparts-2]= keyuse - prev_ref_keyuse;
......@@ -7444,59 +7337,23 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
}
}
keyuse++;
}
} while (keyuse->table == table && keyuse->key == key);
}
else
{
/*
The table is accessed with full table scan, or quick select.
Selectivity of COND(this_table) is already accounted for in
Selectivity of COND(table) is already accounted for in
matching_candidates_in_table().
For COND(this_table, previous_tables) we don't have any meaningful
estimates.
*/
sel= 1;
}
/*
Selectivity and multiple equalities. Consider an example:
select * from t1, t2 where t1.col=t2.col and t2.col<5
Suppose the join order is t1, t2. When equality propagation is used, we
get:
t1: t1.col<5
t2: t2.col<5 // not generated: AND t2.col=t1.col
if we use ref access on table t2, we will not get records for which
"t2.col<5"
when we get to table t2, we will not get records that have "t2.col < 5"
COND(t2) = "t2.col<5"
## a variant with key:
select * from t1, t2 where t1.col=t2.col and t2.col<5 and t2.key=t1.col2
/*
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.
Suppose, we're now looking at selectivity for table t2.
- in case t2 uses full table scan (or quick select): all selectivity is
already accounted for in matching_candidates_in_table().
- in case t2 uses ref access
= if the equality is used for ref access, we have already
discounted its selectivity above
(However, we have not discounted selectivity of the induced
equalities)
= if the equality is not used for ref access, we should still count its
selectivity.
*/
#if 0
for (Field **f_ptr=table->field ; (field= *f_ptr) ; f_ptr++)
{
if (!bitmap_is_set(read_set, field->field_index) ||
......@@ -7514,7 +7371,6 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
}
}
}
#endif
sel*= table_multi_eq_cond_selectivity(join, idx, s, rem_tables,
keyparts, ref_keyuse_steps);
......
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