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MDEV-30812: Improve output cardinality estimates for hash join

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Introduce @@optimizer_switch flag: hash_join_cardinality

When it is on, use EITS statistics to produce tighter bounds for
hash join output cardinality.

Amended by Monty.

Reviewed by: Monty <monty@mariadb.org>
This commit is contained in:
Sergei Petrunia
2023-03-09 17:04:07 +03:00
parent 2eb7bf1ec3
commit 4329ec5d3b
10 changed files with 363 additions and 53 deletions
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41
mysql-test/main/join_cache_cardinality.test Normal file
View File

@ -0,0 +1,41 @@
--source include/have_sequence.inc
# Embedded doesn't have optimizer trace:
--source include/not_embedded.inc
create table t1 (a int, b int, c int);
insert into t1 select seq,seq/2, seq/4 from seq_1_to_100;
create table t2 (a int, b int, c int);
insert into t2 select seq, seq/2, seq/4 from seq_1_to_200;
analyze table t1,t2 persistent for all;
set optimizer_trace=1;
set join_cache_level=6;
set optimizer_switch='hash_join_cardinality=on';
explain select *
from t1, t2
where t1.a=t2.a and t1.a=t2.b and t1.c=t2.c;
set @json= (select trace from information_schema.optimizer_trace);
select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS;
select json_detailed(json_extract(@json, '$**.rest_of_plan[*].rows_for_plan'))
as ROWS_FOR_PLAN;
explain select *
from t1, t2 where t1.c=t2.c;
set @json= (select trace from information_schema.optimizer_trace);
select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS;
select json_detailed(json_extract(@json, '$**.rest_of_plan[*].rows_for_plan'))
as ROWS_FOR_PLAN;
explain select *
from t1 straight_join t2 where t1.c=t2.c and t2.a<30;
set @json= (select trace from information_schema.optimizer_trace);
--echo # Note that rows is the same:
select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS;
--echo # Despite available selectivity:
select json_detailed(json_extract(@json, '$**.selectivity_for_columns')) as JS;
drop table t1,t2;