Hey list -

As many are aware, we’ve been looking for the one MySQL driver to rule them 
all.  As has been the case for some weeks now, that driver is PyMySQL, meeting 
all the critical requirements we have of:  1. pure python, so eventlet 
patchable, 2. Python 3 support 3. Is released on Pypi (which is what 
disqualifies MySQL-connector-Python).

I have experience with PyMySQL and I was at first a little skeptical that it’s 
ready for openstack’s level of activity, so I offered to have oslo.db write up 
a full review of everything we know about all the MySQL drivers, including that 
I’d evaluate PyMySQL and try to put some actual clue behind my vague notions.   

I finally got around to writing up the code review portion, so that we at least 
have awareness of what we’re getting with PyMySQL.  This is also a document 
that I’m very much hoping we can use to get the PyMySQL developers involved 
with.   Basically PyMySQL is fine, it lacks some polish and test coverage that 
can certainly be added, and as far as performance, we’re going to be really 
disappointed with pure-Python MySQL drivers in general, though PyMySQL itself 
can still be improved within the realm of pure Python.  It at least allows for 
eventlet monkey patching, so that we will for the first time be able to observe 
the benefits of some real database concurrency ever since Openstack decided not 
to use threads (if Openstack did in fact ever use normal threads…), which also 
means we will be able to observe the headaches of real database concurrency, 
especially the really scary ones I’ve already observed when working with 
eventlet/gevent style monkeypatching :).

While PyMySQL is lacking test coverage in some areas, has no external 
documentation, and has at least some areas where Python performance can be 
improved, the basic structure of the driver is perfectly fine and 
straightforward.  I can envision turning this driver into a total monster, 
adding C-speedups where needed but without getting in the way of async 
patching, adding new APIs for explicit async, and everything else.   However, 
I’ve no idea what the developers have an appetite for.

Please review the document at 

- mike

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