On 4/30/15 11:16 AM, Dan Smith wrote:
There is an open discussion to replace mysql-python with PyMySQL, but
PyMySQL has worse performance:
https://wiki.openstack.org/wiki/PyMySQL_evaluation
My major concern with not moving to something different (i.e. not based
on the C library) is the threading problem. Especially as we move in the
direction of cellsv2 in nova, not blocking the process while waiting for
a reply from mysql is going to be critical. Further, I think that we're
likely to get back a lot of performance from a supports-eventlet
database connection because of the parallelism that conductor currently
can only provide in exchange for the footprint of forking into lots of
workers.
If we're going to move, shouldn't we be looking at something that
supports our threading model?
yes, but at the same time, we should change our threading model at the
level of where APIs are accessed to refer to a database, at the very
least using a threadpool behind eventlet. CRUD-oriented database
access is faster using traditional threads, even in Python, than using
an eventlet-like system or using explicit async. The tests at
http://techspot.zzzeek.org/2015/02/15/asynchronous-python-and-databases/
show this. With traditional threads, we can stay on the C-based MySQL
APIs and take full advantage of their speed.
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