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MDEV-9750: Quick memory exhaustion with 'extended_keys=on' ...

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(Variant #5, full patch, for 10.5)

Do not produce SEL_ARG graphs that would yield huge numbers of ranges.
Introduce a concept of SEL_ARG graph's "weight". If we are about to
produce a graph whose "weight" exceeds the limit, remove the parts
of SEL_ARG graph that represent the biggest key parts. Do so until
the graph's is within the limit.

Includes
- debug code to verify SEL_ARG graph weight
- A user-visible @@optimizer_max_sel_arg_weight to control the optimization
- Logging the optimization into the optimizer trace.
This commit is contained in:
Sergei Petrunia
2021-01-28 21:43:55 +03:00
parent a2eb974b50
commit c36720388d
11 changed files with 811 additions and 158 deletions
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66
mysql-test/main/range_notembedded.test
View File

@ -31,3 +31,69 @@ from information_schema.optimizer_trace;
set optimizer_trace=@tmp_21958;
drop table t2;
--echo #
--echo # MDEV-9750: Quick memory exhaustion with 'extended_keys=on'...
--echo #
create table t1 (
kp1 int,
kp2 int,
kp3 int,
kp4 int,
key key1(kp1, kp2, kp3,kp4)
);
insert into t1 values (1,1,1,1),(2,2,2,2),(3,3,3,3);
analyze table t1;
show variables like 'optimizer_max_sel_arg_weight';
# 20 * 20 * 20 *20 = 400*400 = 160,000 ranges
set @tmp_9750=@@optimizer_trace;
set optimizer_trace=1;
explain select * from t1 where
kp1 in (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20) and
kp2 in (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20) and
kp3 in (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20) and
kp4 in (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20)
;
set @json= (select json_detailed(JSON_EXTRACT(trace, '$**.range_scan_alternatives'))
from information_schema.optimizer_trace);
--echo # This will show 3-component ranges.
--echo # The ranges were produced, but the optimizer has cut away kp4
--echo # to keep the number of ranges at manageable level:
select left(@json, 500);
--echo ## Repeat the above with low max_weight:
set @tmp9750_weight=@@optimizer_max_sel_arg_weight;
set optimizer_max_sel_arg_weight=20;
explain select * from t1 where
kp1 in (1,2,3,4,5,6,7,8,9,10) and
kp2 in (1,2,3,4,5,6,7,8,9,10) and
kp3 in (1,2,3,4,5,6,7,8,9,10) and
kp4 in (1,2,3,4,5,6,7,8,9,10)
;
set @trace= (select trace from information_schema.optimizer_trace);
set @json= json_detailed(json_extract(@trace, '$**.range_scan_alternatives'));
select left(@json, 500);
set @json= json_detailed(json_extract(@trace, '$**.setup_range_conditions'));
select left(@json, 2500);
--echo ## Repeat the above with a bit higher max_weight:
set @tmp9750_weight=@@optimizer_max_sel_arg_weight;
set optimizer_max_sel_arg_weight=120;
explain select * from t1 where
kp1 in (1,2,3,4,5,6,7,8,9,10) and
kp2 in (1,2,3,4,5,6,7,8,9,10) and
kp3 in (1,2,3,4,5,6,7,8,9,10) and
kp4 in (1,2,3,4,5,6,7,8,9,10)
;
set @json= (select json_detailed(JSON_EXTRACT(trace, '$**.range_scan_alternatives'))
from information_schema.optimizer_trace);
select left(@json, 1500);
set optimizer_max_sel_arg_weight= @tmp9750_weight;
set optimizer_trace=@tmp_9750;
drop table t1;