MySQL Bugs: #5309: MySQL should reserve a connection for the admin (root) user

Bug #5309	MySQL should reserve a connection for the admin (root) user
Submitted:	31 Aug 2004 0:11	Modified:	3 Feb 2006 13:21
Reporter:	Christian Hammers (Silver Quality Contributor) (OCA)	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: General	Severity:	S4 (Feature request)
Version:	4.0.20	OS:	Linux (Debian GNU/Linux)
Assigned to:		CPU Architecture:	Any
Tags:	qc

Description:
Debian bug report http://bugs.debian.org/269114 by Mark Ferlatte:
> When MySQL runs out of threads (due to OS thread limits, ulimit, or
> connection limits), the root MySQL user can no longer connect.  This makes
> it difficult to impossible to debug or repair the ailing MySQL server. 
> MySQL should reserve a thread for connections by the MySQL `root' user.

Note that we are aware that there is already a thread reserverd in case the max_connection limit is set but this does not work in case of a hit ulimit.

bye,

-christian-

How to repeat:
Set "ulimit -u 5" in /etc/init.d/mysql and start some instances. Soon you'll get a:

$ mysql -u root
ERROR 1135: Can't create a new thread (errno 11). If you are not out of available memory, you can consult the manual for a possible OS-dependent bug

-> it's impossible to look at the processlist nor to shutdown the server cleanly

Suggested fix:
Start a maintenance thread as first thread which allowes only root connections.

Thank you for a reasonable feature request.

Bug #47060 looks closely related. We need a reliable way to let SUPER user connect in any case.

Related:
Bug #5309 	MySQL should reserve a connection for the admin (root) user