Bug #100892 Documentation misleading on use of multiple cores
Submitted: 20 Sep 2020 22:19 Modified: 9 Oct 2020 11:36
Reporter: Rick James Email Updates:
Status: Closed Impact on me:
None 
Category:MySQL Server: Documentation Severity:S3 (Non-critical)
Version:all, 5.7, 8.0 OS:Any
Assigned to: CPU Architecture:Any
Tags: core, cpu, documentation

[20 Sep 2020 22:19] Rick James 
Description:
https://dev.mysql.com/doc/refman/5.7/en/faqs-general.html#faq-mysql-support-multi-core

says

A.1.7.

Does MySQL 5.7 work with multi-core processors?

Yes. MySQL is fully multithreaded, and will make use of multiple CPUs, provided that the operating system supports them.

How to repeat:
documentation

See

https://stackoverflow.com/questions/63897746/is-it-possible-to-make-mysql-single-thread-to...

Suggested fix:
Since the A.1.7 can easily be misread to say that one SELECT can use multiple cores, I recommend rewording.

Change to something like:

* In general, no more than 1 core is used for one connection.
* There are a few 'background' threads that make limited use of extra cores. (Example: keeping background I/O tasks moving.)
* In MySQL 8.0, a very few special cases will use multiple cores. https://www.percona.com/blog/2019/01/23/mysql-8-0-14-a-road-to-parallel-query-execution-is...
* If your table(s) is not fully cached, using multiple cores will be futile if it is already I/O-bound.
[21 Sep 2020 5:05] MySQL Verification Team 
Hello Rick,

Thank you for the report and feedback!

Thanks,
Umesh
[9 Oct 2020 11:36] Paul DuBois 
Posted by developer:
 
Updated, thanks for the feedback.