Connection statuses

[K Young]

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
<http://nginx.org/en/docs/http/ngx_http_stub_status_module.html#data> in
Open, right?

Is "Active" on the status demo <http://demo.nginx.com/status.html> =
read+write?

On Thu, Feb 19, 2015 at 8:02 AM, Maxim Dounin <mdounin at mdounin.ru> wrote:

> Hello!
>
> 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
> are
> > 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?
>
> Writing.
>
> >    - While waiting for new client requests on an open connection, is the
> >    connection in a waiting state?
>
> Yes.
>
> > Is the attached sketch of the above connection states correct?
> (underneath
> > "READ" it says "request++" to indicate that this is where the request
> > counter gets incremented).
> > [image: Inline image 1]
>
> Mostly, see above.
>
> --
> Maxim Dounin
> http://nginx.org/
>
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>
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