[openstack-dev] [all] DevStack switching from MySQL-python to PyMySQL

Mike Bayer mbayer at redhat.com
Thu Jun 18 19:47:16 UTC 2015

On 6/18/15 1:28 PM, Matt Riedemann wrote:
> It's not only neutron, I saw some pymysql failures in nova the other 
> day for 'too many connections' or some such related error.

"too many connections" is an error raised by MySQL when more connections 
are attempting to connect than the max_connections setting.  It defaults 
to 100 but it is often set at 1024 in distributions.    An Openstack 
application that uses oslo.db will go through oslo.db's create_engine() 
routine which defaults the max number of connections per python process 
to 15, and when the process is idle, this drops to 5.

Which means, there have to be over 60 python processes all hitting the 
DB at the max to get that error, if max_connections is at 1024.    Or 
the connection pool is totally broken (e.g. with eventlet monkeypatching 
perhaps), which would be a critical issue for me to fix.

So I'd love to see how the "too many connections" error actually 
happens.  Please share whatever you have on that.

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