[openstack-dev] [oslo.db] PyMySQL review

Doug Hellmann doug at doughellmann.com
Thu Jan 29 13:49:26 UTC 2015

On Wed, Jan 28, 2015, at 07:57 PM, Johannes Erdfelt wrote:
> On Wed, Jan 28, 2015, Vishvananda Ishaya <vishvananda at gmail.com> wrote:
> > On Jan 28, 2015, at 4:03 PM, Doug Hellmann <doug at doughellmann.com> wrote:
> > > I hope someone who was around at the time will chime in with more detail
> > > about why green threads were deemed better than regular threads, and I
> > > look forward to seeing your analysis of a change. There is already a
> > > thread-based executor in oslo.messaging, which *should* be usable in the
> > > applications when you remove eventlet.
> > 
> > Threading was never really considered. The initial version tried to get a
> > working api server up as quickly as possible and it used tonado. This was
> > quickly replaced with twisted since tornado was really new at the time and
> > had bugs. We then switched to eventlet when swift joined the party so we
> > didn’t have multiple concurrency stacks.
> > 
> > By the time someone came up with the idea of using different concurrency
> > models for the api server and the backend services, we were already pretty
> > far down the greenthread path.
> Not sure if it helps more than this explanation, but there was a
> blueprint and accompanying wiki page that explains the move from twisted
> to eventlet:
> https://blueprints.launchpad.net/nova/+spec/unified-service-architecture
> https://wiki.openstack.org/wiki/UnifiedServiceArchitecture

Thanks Vish & Johannes, that's good background. There are a lot of
factors to consider, and having a full picture of the history of how we
got to where we are will help us make informed decisions about any
proposed changes.


> JE
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