Details
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Bug
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Status: Closed (View Workflow)
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Critical
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Resolution: Duplicate
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10.5, 10.6, 10.11, 11.1, 11.2, 11.4, 11.5, 11.6
Description
2024-06-21 Update
This issue appeared to be a combination of two problems:
MDEV-34417Wrong result set with utf8mb4_danish_ci and BNLH join- MDEV-34427 BNL-H has not optimal implementation for varchar type
All further work will be done under terms of the above two tickets.
The original report
Testcase:
1. Enable Block Nested Loop Hash (BNLH):
set join_cache_level =3; |
2. Variables join_buffer_size and join_buffer_space_limit were used with default value (They can be changed, but the difference in execution time will still remain)
+-------------------------+----------------------+ |
| Variable_name | Value |
|
+-------------------------+----------------------+ |
| join_buffer_size | 262144 |
|
| join_buffer_space_limit | 2097152 |
|
+-------------------------+----------------------+ |
3. Create table with charset=latin1 or charset=utf8mb4:
CREATE TABLE t1(col1 VARCHAR(500)) engine=INNODB character set latin1 collate latin1_swedish_ci; |
CREATE TABLE t2(col2 VARCHAR(500)) engine=INNODB character set latin1 collate latin1_swedish_ci; |
or
CREATE TABLE t1(col1 VARCHAR(500)) engine=INNODB character set utf8mb4 collate utf8mb4_general_ci; |
CREATE TABLE t2(col2 VARCHAR(500)) engine=INNODB character set utf8mb4 collate utf8mb4_general_ci; |
4. Fill out the tables
insert into t1 select FLOOR(1 + (RAND() * 200000)) from seq_1_to_200000; |
insert into t2 select FLOOR(1 + (RAND() * 20000)) from seq_1_to_200000; |
5. Execute the query:
select max(A.col1) from t1 A, t2 B where A.col1=B.col2; |
Results for v. 11.6:
Debug build:
| latin1 | utf8mb4 |
|---|---|
| 7 min 6,426 sec | 54 min 2,303 sec |
Release build:
| latin1 | utf8mb4 |
|---|---|
| 17,266 sec | 8 min 21,989 sec |
The results of statistics collected using perf are also attached to the task.
Attachments
Issue Links
- duplicates
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- Closed
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- Open
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- relates to
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MDEV-19123 Change default charset from latin1 to utf8mb4
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- In Testing
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MDEV-34232 Check performance of BNL-H vs MySQL's hash join
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- Open
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- Closed
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- Open
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