Bug #98015 Innodb parallel work

• Submitted: 18 Dec 2019 1:12
• Modified: 19 Dec 2019 4:13
• Reporter: 희윤 윤
• Status: Not a Bug
• Category: MySQL Server: InnoDB storage engine
• Severity: S3 (Non-critical)
• Version: 8.0.18
• OS: Linux
• CPU Architecture: x86
• Tags: parallel, parallel create index, parallel insert, parallel work

[18 Dec 2019 1:12] 희윤 윤

Description:
For parallel , use innodb_parallel_read_threads to set 8 and 1

For select count(*) from table (4.7 billion), there was no difference in speed, and 8 may be slower.

For table management of bulk data, parallels must be performed in various places, such as create index and parallel insert ..

test case)

mysql> set local innodb_parallel_read_threads=1;
Query OK, 0 rows affected (0.00 sec)

mysql> select count(*) from uitem_prc_yhy;
+-----------+
| count(*)  |
+-----------+
| 487835240 |
+-----------+
1 row in set (2 min 32.58 sec)

mysql> set local innodb_parallel_read_threads=4;
Query OK, 0 rows affected (0.00 sec)

mysql> select count(*) from uitem_prc_yhy;
+-----------+
| count(*)  |
+-----------+
| 487835240 |
+-----------+
1 row in set (2 min 37.41 sec)

mysql> set local innodb_parallel_read_threads=4;
Query OK, 0 rows affected (0.00 sec)

mysql> select count(*) from uitem_prc_yhy;
+-----------+
| count(*)  |
+-----------+
| 487835240 |
+-----------+
1 row in set (2 min 31.33 sec)

How to repeat:
develop this features

[18 Dec 2019 14:15] MySQL Verification Team

Hello Mr. 희윤 윤,

Thank you for your bug report.

However, this is not a bug.

Seems like you have not read our latest 8.0 Reference Manual.

It says clearly there that the session variable that you are mentioning  defines the number of threads that can be used for parallel clustered index reads.

select count(*) from ......         is doing the scanning of all data pages in the table. Hence, there you can not have parallelism, nor in reading non-clustered indices.

Clearly and definitely not a bug !!!!

[19 Dec 2019 4:13] 희윤 윤

hello Sinisa Milivojevic

How can I read PK PARALLEL?

[19 Dec 2019 13:01] MySQL Verification Team

Hi,

As I wrote, this is all explained in our Reference Manual.

Also, I would like to inform you that this is not a site for free support, so please stop asking questions.