[openstack-dev] [nova] [all] Excessively high greenlet default + excessively low connection pool defaults leads to connection pool latency, timeout errors, idle database connections / workers

Clayton O'Neill clayton at oneill.net
Thu Jan 7 15:48:34 UTC 2016

On Thu, Jan 7, 2016 at 10:44 AM, Mike Bayer <mbayer at redhat.com> wrote:
> On 01/07/2016 07:39 AM, Clayton O'Neill wrote:
>> On Thu, Jan 7, 2016 at 2:49 AM, Roman Podoliaka <rpodolyaka at mirantis.com> wrote:
>>> In each child process eventlet WSGI server calls accept() in a loop to
>>> get a client socket from the kernel and then puts into a greenlet from
>>> a pool for processing:
>> It’s worse than that.  What I’ve seen (via strace) is that eventlet actually
>> converts socket into a non-blocking socket, then converts that accept() into a
>> epoll()/accept() pair in every child.  Then when a connection comes in, every
>> child process wakes up out of poll and races to try to accept on the the
>> non-blocking socket, and all but one of them fails.
> is that eventlet-specific or would we see the same thing in gevent ?

I’m not sure.  For eventlet it’s a natural consequence of most of this being
implemented in Python.  It looks like some of this is implemented in C in
gevent, so they may handle the situation differently.

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