Meaning of http_resp_size

[Steve Webster]

Hi,

I'm attempting to tune our first production varnish server (fronting an API) and have a question about the http_resp_size run-time parameter. The description of this parameter in the varnishd documentation at https://www.varnish-cache.org/docs/3.0/reference/varnishd.html is:

"Maximum number of bytes of HTTP backend resonse we will deal with. This is a limit on all bytes up to the double blank line which ends the HTTP request. The memory for the request is allocated from the worker workspace (param: sess_workspace) and this parameter limits how much of that the request is allowed to take up."

The default value listed for this field is 32kb. The above description makes it sound like any backend response that exceeds the default http_resp_size of 32kb will not be handled (dropped, or at least not cached) by varnish. However, I'm happily able to request images of 200kb and up from this varnish instance, and can confirm that the it is being properly cached.

If http_resp_size is not a limit on the total size of the backend response that can be handled by varnishd, what effect does it actually have on varnishd at runtime?

Cheers,

Steve

-- 
Steve Webster
Web Architect
LOVEFiLM

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