Open Stack

On Thu, Apr 16, 2015 at 01:27:51PM -0400, Jay Pipes wrote:
> On 04/16/2015 09:54 AM, Sean Dague wrote:
> >On 04/16/2015 05:20 PM, Qiming Teng wrote:
> >>
> >>Wondering if there is something misconfigured in my devstack
> >>environment, which was reinstalled on RHEL7 about 10 days ago.
> >>I'm often running into mysql connections problem as shown below:
> >>
> >>$ mysql
> >>ERROR 1040 (HY000): Too many connections
> >>
> >>When I try dump the mysql connection list, I'm getting the followng
> >>result after a 'systemctl restart mariadb.service':
> >>
> >>$ mysqladmin processlist | grep nova | wc -l
> >>125
> >>
> >>Most of the connections are at Sleep status:
> >>
> >>$ mysqladmin processlist | grep nova | grep Sleep | wc -l
> >>123
> >>
> >>As for the workload, I'm currently only running two VMs in a multi-host
> >>devstack environment.
> >>
> >>So, my questions:
> >>
> >>   - Why do we have so many mysql connections from nova?
> >>   - Is it possible this is caused some misconfigurations?
> >>   - 125 connections in such a toy setup is insane, any hints on nailing
> >>     down the connections to the responsible nova components?
> >>
> >>Thanks.
> >>
> >>Regards,
> >>   Qiming
> >
> >No, that's about right. It's 1 connection per worker. By default most
> >daemons start 1 worker per processor. Each OpenStack service has a bunch
> >of daemons. It all adds up pretty quick.
> 
> And just to add to what Sean says above, there's nothing inherently
> wrong with sleeping connections to MySQL. What *is* wrong, however,
> is that the default max_connections setting in my.cnf is 150. :( I
> frequently recommend upping that to 2000 or more on any modern
> hardware or decent sized VM.
> 
> Best,
> -jay
> 
Thanks, guys. So the key takeaway for me is:

 - 100~200 mysql connections is not big problem, provided those
   connections are sleeping;
 - Tuning mysql to support larger number of user connections is a
   must;
 - Number of mysql connections is not proportional to the number of
   VMs, it is more related to the number of cores, number of workers
   etc.

Regards,
  Qiming