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Change cost for REF to take into account cost for 1 extra key read_next

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The main difference in code path between EQ_REF and REF is that for
REF we have to do an extra read_next on the index to check that there
is no more matching rows.

Before this patch we added a preference of EQ_REF by ensuring that REF
would always estimate to find at least 2 rows.

This patch adds the cost of the extra key read_next to REF access and
removes the code that limited REF to at least 2 rows. For some queries
this can have a big effect as the total estimated rows will be halved
for each REF table with 1 rows.

multi_range cost calculations are also changed to take into account
the difference between EQ_REF and REF.

The effect of the patch to the test suite:
- About 80 test case changed
- Almost all changes where for EXPLAIN where estimated rows for REF
  where changed from 2 to 1.
- A few test cases using explain extended had a change of 'filtered'.
  This is because of the estimated rows are now closer to the
  calculated selectivity.
- A very few test had a change of table order.
  This is because the change of estimated rows from 2 to 1 or the small
  cost change for REF
  (main.subselect_sj_jcl6, main.group_by, main.dervied_cond_pushdown,
  main.distinct, main.join_nested, main.order_by, main.join_cache)
- No key statistics and the estimated rows are now smaller which cased
  estimated filtering to be lower.
  (main.subselect_sj_mat)
- The number of total rows are halved.
  (main.derived_cond_pushdown)
- Plans with 1 row changed to use RANGE instead of REF.
  (main.group_min_max)
- ALL changed to REF
  (main.key_diff)
- Key changed from ref + index_only to PRIMARY key for InnoDB, as
  OPTIMIZER_ROW_LOOKUP_COST + OPTIMIZER_ROW_NEXT_FIND_COST is smaller than
  OPTIMIZER_KEY_LOOKUP_COST + OPTIMIZER_KEY_NEXT_FIND_COST.
  (main.join_outer_innodb)
- Cost changes printouts
  (main.opt_trace*)
- Result order change
  (innodb_gis.rtree)
This commit is contained in:
Monty
2022-12-27 14:49:27 +02:00
parent b5df077e85
commit 3fa99f0c0e
81 changed files with 765 additions and 740 deletions
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12
mysql-test/main/subselect_exists2in.result
View File

@ -52,7 +52,7 @@ explain extended
SELECT * FROM t1 WHERE EXISTS ( SELECT a FROM t3 WHERE t3.b = t1.a);
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 index aa aa 4 NULL 2 100.00 Using where; Using index
1 PRIMARY t3 ref bb bb 4 test.t1.a 2 50.00 FirstMatch(t1)
1 PRIMARY t3 ref bb bb 4 test.t1.a 1 100.00 FirstMatch(t1)
Warnings:
Note 1276 Field or reference 'test.t1.a' of SELECT #2 was resolved in SELECT #1
Note 1003 select `test`.`t1`.`a` AS `a` from `test`.`t1` semi join (`test`.`t3`) where `test`.`t3`.`b` = `test`.`t1`.`a`
@ -65,7 +65,7 @@ explain extended
SELECT * FROM t1 WHERE EXISTS ( SELECT a FROM t3 WHERE t3.b = t1.a);
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 index NULL aa 4 NULL 2 100.00 Using where; Using index
2 DEPENDENT SUBQUERY t3 index_subquery bb bb 4 func 2 100.00
2 DEPENDENT SUBQUERY t3 index_subquery bb bb 4 func 1 100.00
Warnings:
Note 1276 Field or reference 'test.t1.a' of SELECT #2 was resolved in SELECT #1
Note 1003 /* select#1 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where <in_optimizer>(`test`.`t1`.`a`,<exists>(<index_lookup>(<cache>(`test`.`t1`.`a`) in t3 on bb)))
@ -91,7 +91,7 @@ explain extended
SELECT * FROM t1 WHERE EXISTS ( SELECT a FROM t3 WHERE t3.b = t1.a);
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 index NULL aa 4 NULL 2 100.00 Using where; Using index
2 DEPENDENT SUBQUERY t3 ref bb bb 4 test.t1.a 2 100.00
2 DEPENDENT SUBQUERY t3 ref bb bb 4 test.t1.a 1 100.00
Warnings:
Note 1276 Field or reference 'test.t1.a' of SELECT #2 was resolved in SELECT #1
Note 1003 /* select#1 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where exists(/* select#2 */ select `test`.`t3`.`a` from `test`.`t3` where `test`.`t3`.`b` = `test`.`t1`.`a` limit 1)
@ -391,7 +391,7 @@ explain extended
SELECT * FROM t1 WHERE EXISTS ( SELECT * FROM t3 WHERE t3.b = t1.a and t3.b1 = t1.a1);
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t3 index bb bb 8 NULL 2 100.00 Using where; Using index; LooseScan
1 PRIMARY t1 ref aa aa 8 test.t3.b,test.t3.b1 2 50.00 Using index
1 PRIMARY t1 ref aa aa 8 test.t3.b,test.t3.b1 1 50.00 Using index
Warnings:
Note 1276 Field or reference 'test.t1.a' of SELECT #2 was resolved in SELECT #1
Note 1276 Field or reference 'test.t1.a1' of SELECT #2 was resolved in SELECT #1
@ -405,7 +405,7 @@ explain extended
SELECT * FROM t1 WHERE EXISTS ( SELECT * FROM t3 WHERE t3.b = t1.a and t3.b1 = t1.a1);
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 index NULL aa 8 NULL 2 100.00 Using where; Using index
2 DEPENDENT SUBQUERY t3 index_subquery bb bb 8 func,func 2 100.00 Using index; Using where
2 DEPENDENT SUBQUERY t3 index_subquery bb bb 8 func,func 1 100.00 Using index; Using where
Warnings:
Note 1276 Field or reference 'test.t1.a' of SELECT #2 was resolved in SELECT #1
Note 1276 Field or reference 'test.t1.a1' of SELECT #2 was resolved in SELECT #1
@ -433,7 +433,7 @@ explain extended
SELECT * FROM t1 WHERE EXISTS ( SELECT * FROM t3 WHERE t3.b = t1.a and t3.b1 = t1.a1);
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 index NULL aa 8 NULL 2 100.00 Using where; Using index
2 DEPENDENT SUBQUERY t3 ref bb bb 8 test.t1.a,test.t1.a1 2 100.00 Using index
2 DEPENDENT SUBQUERY t3 ref bb bb 8 test.t1.a,test.t1.a1 1 100.00 Using index
Warnings:
Note 1276 Field or reference 'test.t1.a' of SELECT #2 was resolved in SELECT #1
Note 1276 Field or reference 'test.t1.a1' of SELECT #2 was resolved in SELECT #1