MySQL Bugs: #79606: Add super

Bug #79606	Add super_connection option
Submitted:	11 Dec 2015 16:06	Modified:	12 Feb 2018 8:08
Reporter:	Zhenye Xie (OCA)	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Options	Severity:	S4 (Feature request)
Version:	5.7	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	Contribution

Description:
Users with SUPER privileges can use an extra connections when connection count reaches max_connections.
But the number of the reserved connections can not be changed. In some cases, more reserved connections is required for maintenance or other reason.

How to repeat:
When connections is full, users with SUPER privileges can have more than one reserved connection and can change it dynamically.

Suggested fix:
Add an option super_connection to specify the reserved connections for SUPER users with default value 1.

pull request:

https://github.com/mysql/mysql-server/pull/34

Contribution submitted via Github - add super_connections option (*) Contribution by Zhenye Xie (Github xiezhenye, mysql-server/pull/34#issuecomment-169582234): I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Contribution: git_patch_53410641.txt (text/plain), 3.21 KiB.

Hello Zhenye Xie,

Thank you for the report and contribution.

Thanks,
Umesh

Thank you for your reasonable feature request.
I believe this is not the only place the check needs to be amended though.
The actual check is done at the end of acl_authenticate() and the valid_connection_count() is used to implement it to observe the layering between the thread manager and the rest of the server code. 
We need to both allow more than max_connections + 1 to be created and we need to check properly that these were used for people with SUPER_ACL (or CONNECTION_ADMIN in 8.0). 
Due to our migration to dynamic privileges in 8.0 I believe a more generic name fo the variable is in order too. Something along the lines of reserved_privileged_connections or some such.