Is the limit_rate per tcp session or per HTTP request?

Valentin V. Bartenev vbart at
Mon Dec 21 12:36:48 UTC 2015

On Monday 21 December 2015 13:18:43 Stefan Hellkvist wrote:
> On Mon, Dec 21, 2015 at 12:26 PM, Ruslan Ermilov <ru at> wrote:
> > On Mon, Dec 21, 2015 at 11:00:09AM +0100, Stefan Hellkvist wrote:
> > > Hi,
> > >
> > > From reading the code and the docs I have gotten the impression that
> > > limit_rate (and limit_rate_after) is per ngx_connection which (I think)
> > > means that it is per HTTP request and not per socket. Am I right in this
> > > conclusion or is the limit actually per socket/TCP connection?
> >
> > The docs at says it clearly that the limit
> > is set per a request, and describes one of the possible cases how this
> > limit can be "avoided" by the client.
> >
> > The limit is implemented on the ngx_connection_t level which is usually
> > mapped 1:1 to a physical connection.
> >
> In our case we have clients that use pipelining where several requests
> share the same tcp session. An ngx_connection_t is mapped 1:1 to the
> requests and not to the physical socket in this case, am I right?

Regardless of the internal implementation it's better to think that
"limit_rate" and "limit_rate_after" currently work per request only.

The ngx_connection_t is mapped to the physical socket, but the number
of sent bytes is reseted to zero on each request in the connection.  

> >
> > > If our conclusion are right - that the limit is per HTTP request and not
> > > per socket so that a chunked download would not be limited - does anyone
> > > have any suggestion how we would go about to introduce a limit also on
> > > socket level? I don't mind hacking away at the code, but perhaps someone
> > > out there has already looked into this?
> >
> > I know that Valentin (CC:ed) was working on the limit_rate module that
> > improves things, including variables support and extening the limitation
> > beyond only "per request".  It should become possible to limit byte rate
> > per IP, for example.
> >
> That is great news that there is someone looking into it. Would this
> limit_rate module also support limiting the rate in pipelined requests? The
> use case I am looking at specifically is to control the download rate of a
> client that pipelines requests for HLS chunks (Apple's HTTP live
> streaming), so the same tcp connection is being used for several
> downloadable chunks. I would need to have the limit_rate_after as it is
> today, but on socket rather than http request, to allow the video buffer to
> fill up quickly during the requests for the first chunks,  but would like
> to limit the rate of the following pipelined request once the video
> playback buffer is full.

Yes, I'll keep in mind this use case.

  wbr, Valentin V. Bartenev

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