k at datadoghq.com
Thu Feb 19 15:12:02 UTC 2015
Thanks Maxim, that's what I needed to know.
How common would you say it is to use accept filters / deferred accept on
nginx in production?
Also to be perfectly certain: connections.idle
<http://nginx.org/en/docs/http/ngx_http_status_module.html#data> in Plus is
the same as Waiting
Is "Active" on the status demo <http://demo.nginx.com/status.html> =
On Thu, Feb 19, 2015 at 8:02 AM, Maxim Dounin <mdounin at mdounin.ru> wrote:
> On Wed, Feb 18, 2015 at 09:25:01PM -0500, K Young wrote:
> > Hello, I've been reading through nginx source to understand the metrics
> > <http://nginx.org/en/docs/http/ngx_http_stub_status_module.html> that
> > reported. I've got an idea of what is happening, but since the flow is
> > asynchronous, I'm not 100% confident, and would love your feedback.
> > Is the following correct?
> > - 'accepts' is incremented when a worker gets a new request for a
> > connection from the OS
> > - 'handled' is incremented when a worker gets a new connection for a
> > request
> > And then once a connection is opened:
> > - 'active' is incremented (actually, it is incremented right before
> > 'handled', but will be decremented if the worker doesn't handle the
> > connection request).
> > - then the connection briefly goes into a waiting state while the
> > request is waiting to be processed
> > - then the connection goes into a short reading state while request
> > headers are read. Simultaneously, 'request' is incremented every time
> a new
> > request header begins to be read.
> > - then the connection goes into a writing state while all work is done
> > by nginx and by upstream components
> > - then if the connection will be kept alive, it goes back into waiting
> > state, which is synonymous with 'idle'
> > - finally when the connection is closed, active is decremented
> > The things I'm least certain of about the 'waiting' state:
> > - Does active always sum up to waiting+reading+writing?
> Generally yes. There are nuances with SPDY where additional
> connections are emulated for SPDY streams being handled, and
> waiting+reading+writing may be bigger than active.
> > - Does each new connection enter a waiting state just before it goes
> > into the reading state?
> No. If there are data available right after connect (this usually
> happens with accept filters / deferred accept), nginx will not
> mark a newly accepted connection as waiting, and will start
> reading a request directly.
> > - While waiting for upstream responses, is the connection in writing
> > state or waiting state?
> > - While waiting for new client requests on an open connection, is the
> > connection in a waiting state?
> > Is the attached sketch of the above connection states correct?
> > "READ" it says "request++" to indicate that this is where the request
> > counter gets incremented).
> > [image: Inline image 1]
> Mostly, see above.
> Maxim Dounin
> nginx mailing list
> nginx at nginx.org
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